SPC MD 875

1 year 2 months ago
MD 0875 CONCERNING TORNADO WATCH 277... FOR SOUTHWEST/SOUTH-CENTRAL IA
Mesoscale Discussion 0875 NWS Storm Prediction Center Norman OK 0320 PM CDT Tue May 21 2024 Areas affected...Southwest/South-Central IA Concerning...Tornado Watch 277... Valid 212020Z - 212145Z The severe weather threat for Tornado Watch 277 continues. SUMMARY...A localized corridor favorable for strong tornadoes exists across southwest/south-central Iowa, including Des Moines vicinity. DISCUSSION...Pair of supercells on the southern end of the line of storms extending across western IA have recently shown notable intensification, with rotational velocity recently estimated around 50 to 55 kt within the southernmost cell. Strong southerly flow exists ahead of this storm, contributing to strong low-level shear, evidenced by recent 0-500m storm relative-helicity around 200 m2/s2 from DMX VAD. Robust deep-layer shear exists as well, with DMX VAD sampling 0-6 km bulk shear was over 60 kt. Recent mesoanalysis estimates effective-layer STP from 3 to 4 downstream. All of these factors suggest the downstream environment will remain conducive for supercell persistence. Storm motion for this southernmost storm is estimated to be northeasterly at around 45 kt, bring it into the Des Moines vicinity around 2130Z. ..Mosier.. 05/21/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX...OAX... LAT...LON 40719467 41269501 41659451 41949347 41189288 40719467 Read more

SPC Tornado Watch 278 Status Reports

1 year 2 months ago
WW 0278 Status Updates
STATUS REPORT ON WW 278 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 15 S BVO TO 20 SE OJC TO 20 WNW CDJ TO 5 E LWD. ..HART..05/21/24 ATTN...WFO...TSA...ICT...TOP...EAX...SGF... STATUS REPORT FOR WT 278 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS ARC007-015-087-143-212240- AR . ARKANSAS COUNTIES INCLUDED ARE BENTON CARROLL MADISON WASHINGTON KSC011-021-037-099-107-133-212240- KS . KANSAS COUNTIES INCLUDED ARE BOURBON CHEROKEE CRAWFORD LABETTE LINN NEOSHO MOC001-009-011-013-015-025-029-033-037-039-041-043-053-057-059- 061-077-079-081-083-085-089-095-097-101-105-107-109-115-117-119- 121-129-141-145-159-167-171-175-177-185-195-197-209-211-217-225- 212240- MO . MISSOURI COUNTIES INCLUDED ARE Read more

SPC Tornado Watch 277 Status Reports

1 year 2 months ago
WW 0277 Status Updates
STATUS REPORT ON WW 277 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 5 SSW LWD TO 15 SSE FOD TO 20 ENE FRM TO 25 ENE RWF. ..HART..05/21/24 ATTN...WFO...DMX...ARX...DVN...MPX... STATUS REPORT FOR WT 277 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS ILC015-071-073-085-131-161-187-195-212240- IL . ILLINOIS COUNTIES INCLUDED ARE CARROLL HENDERSON HENRY JO DAVIESS MERCER ROCK ISLAND WARREN WHITESIDE IAC005-007-011-013-015-017-019-023-031-033-037-039-043-045-051- 053-055-057-061-065-067-069-075-079-081-083-087-089-095-097-099- 101-103-105-107-111-113-115-117-121-123-125-127-131-135-139-153- 157-163-169-171-177-179-181-183-185-187-189-191-195-197- 212240- IA . IOWA COUNTIES INCLUDED ARE ALLAMAKEE APPANOOSE BENTON BLACK HAWK BOONE BREMER BUCHANAN BUTLER CEDAR CERRO GORDO CHICKASAW CLARKE CLAYTON CLINTON DAVIS DECATUR DELAWARE DES MOINES Read more

SPC MD 874

1 year 2 months ago
MD 0874 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR EASTERN KS...WESTERN MO...NORTHEAST OK...FAR NORTHWEST AR
Mesoscale Discussion 0874 NWS Storm Prediction Center Norman OK 0215 PM CDT Tue May 21 2024 Areas affected...Eastern KS...Western MO...Northeast OK...Far Northwest AR Concerning...Severe potential...Watch likely Valid 211915Z - 212115Z Probability of Watch Issuance...80 percent SUMMARY...Severe thunderstorm development is anticipated this afternoon from eastern Kansas into western Missouri, northeast Oklahoma, and far northwest Arkansas. All severe hazards are possible and a watch will likely be needed soon. DISCUSSION...Visible satellite imagery shows increasingly agitated cumulus ahead of a surface trough extending arcing southeastward into northeast KS and then back southwestward from east-central KS through north-central OK. The airmass preceding this boundary is characterized by temperatures in the mid to upper 80s, dewpoints in the upper 60s/low 70s, and strong buoyancy. Recent mesoanalysis estimates MLCAPE around 2500 J/kg is currently in place, with the 18Z TOP sounding sampling 3100 J/kg. This same sounding revealed that much of the convective inhibition has been eroded, although the warm-layer between 800-700 mb could still result in updrafts struggling to mature. The general expectation is that additional heating should help diminish the effect of that warm layer even more, with both increasing large-scale ascent and convergence along the boundary providing the lift needed for convective initiation. This initiation will likely begin in the northeast KS/Kansas City vicinity before expanding southward/southwestward over time. Deep-layer shear is strong enough to support organized updrafts/supercells, with all severe hazards possible. Given the strong buoyancy, most prominent hazard appears to be large to very large hail. Strong downdrafts appear possible as well. Low-level flow is a bit weaker in this region that areas farther south, resulting in a modest weakness in the hodograph, which could act to inhibit tornadogenesis. However, given the likely organized character to the storms, there is still some tornado potential with any discrete storm. A watch will likely be needed soon to address these hazards. ..Mosier/Guyer.. 05/21/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...SGF...EAX...TSA...TOP...ICT... LAT...LON 39999502 40479441 40339322 38629301 36579381 35999517 36259658 37979582 39999502 Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more

SPC May 21, 2024 2000 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Tue May 21 2024 Valid 212000Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IOWA...NORTHERN MISSOURI...SOUTHWEST WISCONSIN AND NORTHWEST ILLINOIS... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, large hail, and widespread damaging winds, is expected this afternoon through evening, especially across Iowa, Missouri to northern Illinois, southeast Minnesota, and southern Wisconsin. ...20Z Update... A broken line of storms with supercells within continues to get better organized over southwest IA near the surface low, with a possible meso low developing near Red Oak IA as of 1930Z. Low-level shear is very favorable for intense tornadic supercells, with 0-500m SRH over 200 m2/s2 noted on the DMX radar. Pressure falls continue into this region, along with clearing and further destabilization. As such, tornadoes appear imminent across much of IA over the next few hours. Farther south into eastern KS and northern MO, a very unstable air mass has developed here as well, with an impressive 18Z TOP sounding. Steep midlevel lapse rates over 8 C/km with strong deep-layer shear including 50-60 kt speeds around 700 mb will favor downstream supercells producing very large hail with tornado risk. ..Jewell.. 05/21/2024 .PREV DISCUSSION... /ISSUED 1140 AM CDT Tue May 21 2024/ ...Middle/Lower Missouri Valley and Midwest... As an outbreak precursor, a well-organized cluster of storms across south-central/east-central Iowa mid-late this morning has had a history of producing at least isolated/episodic severe weather since the predawn hours. These storms are focused along/north of an outflow-reinforced warm front that will lift northward through late today into tonight. This will be heavily influenced by a highly dynamic mass response to a northeast-moving mid-level shortwave trough that is readily evident in water vapor imagery over the central High Plains this morning. That said, some short-term uncertainties exist as of 15z observational data, with gusty post-convective northeasterly winds still present across south-central Iowa, which relates to some uncertainty with the northward extent of the higher-magnitude severe risk across Minnesota/Wisconsin later today, although latest 16z data features a recent abatement of those northerly winds. Regardless, intense storm development is anticipated into the afternoon across a broad north/south corridor. A synoptically evident and regional outbreak-favorable setup exists, especially by mid/late May standards, highlighted by a coupled upper jet structure over the Upper Midwest, strengthening deep-layer wind fields, and steady cyclogenesis from the Nebraska/Kansas border vicinity this morning northeastward toward the Minnesota/Wisconsin border tonight. Low-level winds will remain strong diurnally ahead of the primary cyclone, but a noteworthy strengthening of mid-level winds 3-7 km AGL (reference 700mb/500mb) will rapidly occur through the afternoon/evening, which will likely have direct outbreak-relevant influences on initial supercell intensity, QLCS evolution and overall fast east-northeastward storm motions later today. Steepening mid-level lapse rates, noted in upstream 12z observed soundings such as Topeka/Dodge City KS and Springfield MO, will overspread an increasingly moist airmass generally characterized by mid/upper 60s F surface dewpoints, contributing to warm-sector MLCAPE to upwards of 2500-3000 J/kg this afternoon. Scattered to numerous thunderstorms, including scattered fast-moving supercells, are expected to initially form over parts of eastern Nebraska by late morning/midday, and into Iowa and northern/central Missouri this afternoon. This will occur as the cold front impinges on a retreating outflow boundary from the morning storms, and an airmass destabilizing rapidly on both sides of the boundary from a combination of diurnal heating and intense warm advection. Additional, initially semi-discrete, supercellular development is also plausible farther east across Iowa this afternoon in vicinity of modifying outflow/warm front. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of Iowa and potentially into southern Minnesota as well, spreading into parts of western/northern Illinois and Wisconsin. Several tornadoes, including some strong with EF2+ potential, are expected, along with large, damaging hail and severe downdrafts. This includes the possibility of long-track supercells/tornadoes and swaths of locally intense wind damage. Later tonight, storms should begin to gradually outrun the corridor of favorable surface-based buoyancy in the evening after crossing the Mississippi River, but may remain well-organized in terms of severe-wind threat across Lake Michigan vicinity. ...Ozarks/Oklahoma to south Texas... Isolated to scattered thunderstorms are expected to form from mid afternoon into evening near the front and dryline, offering large to very large hail and locally severe gusts. Hail at least 3 inches in diameter is possible. A tornado or two is not out of the question, especially in northern areas (Ozarks vicinity) under the fringes of the gradient-flow/deep-shear influence from the ejecting shortwave trough, and with high-CAPE storm-scale processes amid favorable deep shear elsewhere. Renewed storm development, potentially severe, could also occur in the predawn hours of Wednesday across Oklahoma near the front. Though capping from an EML will limit convective potential for much of the day, a combination of strong surface heating, rich boundary- layer moisture, and frontal/dryline lift will weaken MLCINH enough by mid/late afternoon to support deep convective development. Upper 60s to low 70s F surface dewpoints should become common beneath a high equilibrium level (deep troposphere) and steep mid-level lapse rates, supporting a corridor of 3000-4000 J/kg MLCAPE (locally higher). Sufficient veering of winds with height, and effective-shear magnitudes in the 45-60 kt range, will support supercell potential. Activity over Texas my weaken within a few hours after sunset as nocturnal boundary-layer cooling re-establishes the strong capping beneath the EML. However, farther north across parts of Arkansas/Missouri, a weaker EML influence may permit activity to persist later and farther east this evening, before weakening. ...Adirondacks region to northern New England... Widely scattered to scattered thunderstorms should develop over portions of the Adirondacks and White Mountains today, and perhaps also move into the area from nearby parts of extreme eastern Ontario and southernmost Quebec. Damaging gusts and isolated severe hail will be possible. A mid/upper-level shortwave trough and embedded MCV -- related to the significantly severe MCS over Kansas two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern New York/New England and times well with the diurnal-heating cycle there. Activity should form as large-scale DCVA/lift and enhancement of midlevel flow -- preceding the MCV/shortwave trough -- spread atop a destabilized, suitably moist boundary layer, heated to convective temperature over elevated terrain. These processes will erode MLCINH to negligible levels, fostering MLCAPE commonly in the 1000-1500 J/kg range, locally/briefly near 2000 J/kg. Deep shear should remain modest, with effective-shear magnitudes generally 25-35 kt, though enough veering with height in low levels may develop to shape somewhat enlarged hodographs. Multicell and transient supercell modes should predominate, with the severe threat diminishing markedly after sunset. Read more
Checked
5 years 9 months ago
Severe Storms
Storm Prediction Center
Subscribe to Severe Storms feed