SPC Severe Thunderstorm Watch 275 Status Reports

1 year 2 months ago
WW 0275 Status Updates
STATUS REPORT ON WW 275 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 NNE SDA TO 10 SW DSM TO 25 NNE OXV TO 10 NW ALO. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 0868 ..MOSIER..05/21/24 ATTN...WFO...DMX...DVN... STATUS REPORT FOR WS 275 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC003-007-011-013-019-031-039-051-053-055-087-095-101-103-105- 107-113-117-121-123-125-135-157-159-171-173-175-177-179-181-183- 185-211640- IA . IOWA COUNTIES INCLUDED ARE ADAMS APPANOOSE BENTON BLACK HAWK BUCHANAN CEDAR CLARKE DAVIS DECATUR DELAWARE HENRY IOWA JEFFERSON JOHNSON JONES KEOKUK LINN LUCAS MADISON MAHASKA MARION MONROE POWESHIEK RINGGOLD TAMA TAYLOR UNION VAN BUREN WAPELLO WARREN WASHINGTON WAYNE THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES Read more

SPC Severe Thunderstorm Watch 275 Status Reports

1 year 2 months ago
WW 0275 Status Updates
STATUS REPORT ON WW 275 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 NNE SDA TO 10 SW DSM TO 25 NNE OXV TO 10 NW ALO. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 0868 ..MOSIER..05/21/24 ATTN...WFO...DMX...DVN... STATUS REPORT FOR WS 275 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS IAC003-007-011-013-019-031-039-051-053-055-087-095-101-103-105- 107-113-117-121-123-125-135-157-159-171-173-175-177-179-181-183- 185-211640- IA . IOWA COUNTIES INCLUDED ARE ADAMS APPANOOSE BENTON BLACK HAWK BUCHANAN CEDAR CLARKE DAVIS DECATUR DELAWARE HENRY IOWA JEFFERSON JOHNSON JONES KEOKUK LINN LUCAS MADISON MAHASKA MARION MONROE POWESHIEK RINGGOLD TAMA TAYLOR UNION VAN BUREN WAPELLO WARREN WASHINGTON WAYNE THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES Read more

SPC Severe Thunderstorm Watch 275

1 year 2 months ago
WW 275 SEVERE TSTM IA 211115Z - 211800Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 275 NWS Storm Prediction Center Norman OK 615 AM CDT Tue May 21 2024 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Central and southern Iowa * Effective this Tuesday morning and afternoon from 615 AM until 100 PM CDT. * Primary threats include... Scattered damaging winds and isolated significant gusts to 75 mph possible Isolated large hail events to 1.5 inches in diameter possible A tornado or two possible SUMMARY...Clusters of thunderstorms -- including an organized bowing complex initially over eastern NE -- will pose a threat mainly for severe gusts while crossing the watch area from west to east. A tornado or two cannot be ruled out, especially near an outflow boundary draped across central/south-central IA. Isolated large hail is possible. This is a precursor to the main severe-weather threat expected later today, for which we have a "Moderate Risk" outlook. The severe thunderstorm watch area is approximately along and 60 statute miles north and south of a line from 80 miles west of Des Moines IA to 25 miles south southeast of Cedar Rapids IA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU5). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 274... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 65 knots. A few cumulonimbi with maximum tops to 550. Mean storm motion vector 26045. ...Edwards Read more

SPC Center Public Severe Weather Outlook (PWO)

1 year 2 months ago
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0827 AM CDT TUE MAY 21 2024 ...Severe thunderstorms expected over parts of the Midwest this afternoon and tonight... * LOCATIONS... Iowa Northern Illinois Northern Missouri Southern Wisconsin Southeast Minnesota Far Eastern Kansas Eastern Nebraska * HAZARDS... Widespread damaging winds, some hurricane force Several tornadoes, a few intense Widespread large hail, some baseball size * SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. Preparedness actions... Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A watch means that conditions are favorable for severe thunderstorms over the next several hours. If a severe thunderstorm warning is issued for your area, move to a place of safety, ideally in an interior room on the lowest floor of a sturdy building. Read more

SPC Center Public Severe Weather Outlook (PWO)

1 year 2 months ago
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0827 AM CDT TUE MAY 21 2024 ...Severe thunderstorms expected over parts of the Midwest this afternoon and tonight... * LOCATIONS... Iowa Northern Illinois Northern Missouri Southern Wisconsin Southeast Minnesota Far Eastern Kansas Eastern Nebraska * HAZARDS... Widespread damaging winds, some hurricane force Several tornadoes, a few intense Widespread large hail, some baseball size * SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. Preparedness actions... Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A watch means that conditions are favorable for severe thunderstorms over the next several hours. If a severe thunderstorm warning is issued for your area, move to a place of safety, ideally in an interior room on the lowest floor of a sturdy building. Read more

SPC Center Public Severe Weather Outlook (PWO)

1 year 2 months ago
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0827 AM CDT TUE MAY 21 2024 ...Severe thunderstorms expected over parts of the Midwest this afternoon and tonight... * LOCATIONS... Iowa Northern Illinois Northern Missouri Southern Wisconsin Southeast Minnesota Far Eastern Kansas Eastern Nebraska * HAZARDS... Widespread damaging winds, some hurricane force Several tornadoes, a few intense Widespread large hail, some baseball size * SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. Preparedness actions... Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A watch means that conditions are favorable for severe thunderstorms over the next several hours. If a severe thunderstorm warning is issued for your area, move to a place of safety, ideally in an interior room on the lowest floor of a sturdy building. Read more

SPC Center Public Severe Weather Outlook (PWO)

1 year 2 months ago
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0827 AM CDT TUE MAY 21 2024 ...Severe thunderstorms expected over parts of the Midwest this afternoon and tonight... * LOCATIONS... Iowa Northern Illinois Northern Missouri Southern Wisconsin Southeast Minnesota Far Eastern Kansas Eastern Nebraska * HAZARDS... Widespread damaging winds, some hurricane force Several tornadoes, a few intense Widespread large hail, some baseball size * SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. Preparedness actions... Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A watch means that conditions are favorable for severe thunderstorms over the next several hours. If a severe thunderstorm warning is issued for your area, move to a place of safety, ideally in an interior room on the lowest floor of a sturdy building. Read more

SPC Center Public Severe Weather Outlook (PWO)

1 year 2 months ago
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0827 AM CDT TUE MAY 21 2024 ...Severe thunderstorms expected over parts of the Midwest this afternoon and tonight... * LOCATIONS... Iowa Northern Illinois Northern Missouri Southern Wisconsin Southeast Minnesota Far Eastern Kansas Eastern Nebraska * HAZARDS... Widespread damaging winds, some hurricane force Several tornadoes, a few intense Widespread large hail, some baseball size * SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. Preparedness actions... Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A watch means that conditions are favorable for severe thunderstorms over the next several hours. If a severe thunderstorm warning is issued for your area, move to a place of safety, ideally in an interior room on the lowest floor of a sturdy building. Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more

SPC May 21, 2024 1300 UTC Day 1 Convective Outlook

1 year 2 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Tue May 21 2024 Valid 211300Z - 221200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER MUCH OF IA AND NEARBY PARTS OF SOUTHEASTERN MINNESOTA...WISCONSIN...ILLINOIS...AND MISSOURI... ...SUMMARY... An outbreak of severe thunderstorms, including the potential for strong tornadoes, is expected mainly this afternoon to early evening. The greatest threat is over Iowa and parts of adjacent states. ...Synopsis... In mid/upper levels, a persistent, slow-moving cyclone will meander over southern SK through the period, while a separate closed low digs southeastward from northern BC to WA. These will anchor a mean trough extending from the northern Rockies across southern CA and offshore from northern Baja. In the downstream southwesterlies, a shortwave trough was evident in moisture-channel imagery over the High Plains from western NE to northeastern NM. This perturbation should pivot northeastward to southern MN, central IA and northwestern MO by 00Z, then northeastward over western and northern parts of the upper Great Lakes by 12Z tomorrow. At the surface, 11Z analysis showed lows near SUX and CNK, along a cold front arching to southwestern KS and the Raton Mesa. The lows should consolidate today into a more-coherent cyclone center and move to southern MN by 00Z, with cold front to southeastern IA, central MO, and central OK, becoming quasistationary to warm across western OK and the northern TX Panhandle, to a low in southeastern CO. A dryline -- initially analyzed from a frontal intersection over west-central KS south-southwestward to between MAF-FST, should shift eastward today over southern/central OK, northwest/west- central TX, and the Edwards Plateau. By 12Z, the low should become occluded over the Boundary Waters region, with cold front across Lower MI, southern IL, southeastern MO, southern OK, northwest TX, and southeastern NM. ...Upper Mississippi to lower Missouri Valleys... An ongoing, organized band of thunderstorms, with a history of producing several measured severe gusts in central/eastern NE -- will sweep across parts of IA through the remainder of the morning. This activity will overtake isolated strong-severe convection near the outflow boundary, where relatively maximized low-level vorticity and instability will be most strongly juxtaposed. Severe gusts, sporadic large hail, and a tornado or two all are possible. See SPC Severe Thunderstorm Watch 275 and related mesoscale discussions for near-term guidance on this threat. That activity is a precursor to the main event, which is expected to sweep across much of the same areas (and portions of adjoining states) from midday through the evening. Scattered to numerous thunderstorms (including multiple fast-moving supercells) are expected to form over parts of eastern NE from midday into early afternoon, and over IA and northern/central MO 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. Sufficient airmass recovery for a surface-based, all-hazards severe threat is expected across most of IA and probably into southern MN as well, spreading into parts of western/northern IL and WI ahead of the main convective arc. Several tornadoes -- some strong (EF2+ damage potential) are possible, along with large, damaging hail and severe downdrafts. Given potential for cell motions of 45-50 kt, potential exists for a few long-track mesocyclones/tornadoes. The approach of the shortwave trough will increase large-scale lift -- now evident with post-frontal convection over southwestern NE and northwestern KS that may be trackable across southern NE to the earliest substantial convection in the midday hours. The ascent should spread over the region, atop that from the front and surface heating, supporting the development of steep low/middle-level lapse rates. With surface dewpoints recovering into the upper 60s to around 70 F, a corridor of 2000-3000 J/kg MLCAPE should develop over much of IA, with slightly weaker (but still favorable) values clipping parts of southern MN as well. Activity 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. The largest low-level hodographs should be near and north of the remnant outflow boundary, with effective SRH exceeding 300 J/kg -- but will be favorable for potentially tornadic supercells farther south into southern IA and parts of MO as well. ...Ozarks to south Texas... Isolated to scattered thunderstorms are expected to form from midafternoon 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. 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 midlevel 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 TX 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 AR/MO, 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 ON and southernmost QC. 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 KS two days ago -- is apparent in satellite imagery over Lake Huron. This feature will move eastward toward northern NY/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 dark. ..Edwards/Goss.. 05/21/2024 Read more
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Severe Storms
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