Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1153 AM CDT Wed Aug 21 2019 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... Sundowner winds are possible across Santa Barbara county in southern California this evening and may lead to isolated elevated fire weather conditions, but the isolated and short duration of the threat precludes inclusion of an elevated delineation. No changes have been made to the previous outlook. See previous discussion below. ..Bentley.. 08/21/2019 .PREV DISCUSSION... /ISSUED 0136 AM CDT Wed Aug 21 2019/ ...Synopsis... An upper-level shortwave trough will move into the Pacific Northwest and northern Rockies today with an associated surface cold front sweeping east and south through the Pacific Northwest. Hot/dry/unstable conditions are expected to continue across much of the Intermountain West ahead of the cold front and north/west of the subtropical moisture in the Southwest and Rocky Mountains. Elevated conditions may develop just ahead of the cold front across eastern Washington/Oregon, but conditions should be short-lived and followed by cooler, moist air. Isolated thunderstorms are possible along the cold front across portions of the inland Pacific Northwest. Additionally, isolated dry thunderstorms may form across portions of the northern Rockies. However, the forecast airmass change and marginal fuel conditions where storms may develop preclude an isolated dry thunderstorm area. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1132 AM CDT Wed Aug 21 2019 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST/MID-ATLANTIC STATES... ...SUMMARY... Severe thunderstorms are expected this afternoon and evening across parts of the Northeast/Mid-Atlantic States, with other severe storms possible across the central Great Plains. ...Northeast/Mid-Atlantic States... A shortwave trough will continue to progress east-northeastward from eastern New York toward northern New England, while a warm front slowly spreads northward across southern New England. With broken cloud cover lingering in most areas, modest overall destabilization is expected along/south of the warm front where low-level/deep-layer shear will be maximized. The environment will support the possibility of supercells/bowing segments particularly across southeast New York and southern New England, with severe hail/wind possible along with some tornado risk. Multicells with damaging winds are possible farther south within the warm sector. For additional short-term details, see Mesoscale Discussion 1825. ...Kansas/Missouri/far southeast Nebraska to Missouri/Illinois... The remnants of overnight convection continue to decay across the region with cloud cover/outflow influencing an effective boundary across southern portions of Kansas/Missouri. Surface-based thunderstorms should develop/intensify later this afternoon particularly across southern/eastern Kansas into western Missouri within a moist/unstable environment. Relatively weak tropospheric winds may limit overall storm organization, but the strongest storms will pose a damaging wind/severe hail risk. ...Wyoming/Colorado Front Range to central High Plains... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern Wyoming across central/southern Colorado, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Mid-level flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ..Guyer/Coniglio.. 08/21/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1132 AM CDT Wed Aug 21 2019 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST/MID-ATLANTIC STATES... ...SUMMARY... Severe thunderstorms are expected this afternoon and evening across parts of the Northeast/Mid-Atlantic States, with other severe storms possible across the central Great Plains. ...Northeast/Mid-Atlantic States... A shortwave trough will continue to progress east-northeastward from eastern New York toward northern New England, while a warm front slowly spreads northward across southern New England. With broken cloud cover lingering in most areas, modest overall destabilization is expected along/south of the warm front where low-level/deep-layer shear will be maximized. The environment will support the possibility of supercells/bowing segments particularly across southeast New York and southern New England, with severe hail/wind possible along with some tornado risk. Multicells with damaging winds are possible farther south within the warm sector. For additional short-term details, see Mesoscale Discussion 1825. ...Kansas/Missouri/far southeast Nebraska to Missouri/Illinois... The remnants of overnight convection continue to decay across the region with cloud cover/outflow influencing an effective boundary across southern portions of Kansas/Missouri. Surface-based thunderstorms should develop/intensify later this afternoon particularly across southern/eastern Kansas into western Missouri within a moist/unstable environment. Relatively weak tropospheric winds may limit overall storm organization, but the strongest storms will pose a damaging wind/severe hail risk. ...Wyoming/Colorado Front Range to central High Plains... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern Wyoming across central/southern Colorado, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Mid-level flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ..Guyer/Coniglio.. 08/21/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1132 AM CDT Wed Aug 21 2019 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST/MID-ATLANTIC STATES... ...SUMMARY... Severe thunderstorms are expected this afternoon and evening across parts of the Northeast/Mid-Atlantic States, with other severe storms possible across the central Great Plains. ...Northeast/Mid-Atlantic States... A shortwave trough will continue to progress east-northeastward from eastern New York toward northern New England, while a warm front slowly spreads northward across southern New England. With broken cloud cover lingering in most areas, modest overall destabilization is expected along/south of the warm front where low-level/deep-layer shear will be maximized. The environment will support the possibility of supercells/bowing segments particularly across southeast New York and southern New England, with severe hail/wind possible along with some tornado risk. Multicells with damaging winds are possible farther south within the warm sector. For additional short-term details, see Mesoscale Discussion 1825. ...Kansas/Missouri/far southeast Nebraska to Missouri/Illinois... The remnants of overnight convection continue to decay across the region with cloud cover/outflow influencing an effective boundary across southern portions of Kansas/Missouri. Surface-based thunderstorms should develop/intensify later this afternoon particularly across southern/eastern Kansas into western Missouri within a moist/unstable environment. Relatively weak tropospheric winds may limit overall storm organization, but the strongest storms will pose a damaging wind/severe hail risk. ...Wyoming/Colorado Front Range to central High Plains... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern Wyoming across central/southern Colorado, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Mid-level flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ..Guyer/Coniglio.. 08/21/2019 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1132 AM CDT Wed Aug 21 2019 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHEAST/MID-ATLANTIC STATES... ...SUMMARY... Severe thunderstorms are expected this afternoon and evening across parts of the Northeast/Mid-Atlantic States, with other severe storms possible across the central Great Plains. ...Northeast/Mid-Atlantic States... A shortwave trough will continue to progress east-northeastward from eastern New York toward northern New England, while a warm front slowly spreads northward across southern New England. With broken cloud cover lingering in most areas, modest overall destabilization is expected along/south of the warm front where low-level/deep-layer shear will be maximized. The environment will support the possibility of supercells/bowing segments particularly across southeast New York and southern New England, with severe hail/wind possible along with some tornado risk. Multicells with damaging winds are possible farther south within the warm sector. For additional short-term details, see Mesoscale Discussion 1825. ...Kansas/Missouri/far southeast Nebraska to Missouri/Illinois... The remnants of overnight convection continue to decay across the region with cloud cover/outflow influencing an effective boundary across southern portions of Kansas/Missouri. Surface-based thunderstorms should develop/intensify later this afternoon particularly across southern/eastern Kansas into western Missouri within a moist/unstable environment. Relatively weak tropospheric winds may limit overall storm organization, but the strongest storms will pose a damaging wind/severe hail risk. ...Wyoming/Colorado Front Range to central High Plains... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern Wyoming across central/southern Colorado, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Mid-level flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ..Guyer/Coniglio.. 08/21/2019 Read more

MD 1825 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR NORTHERN MID ATLANTIC COAST REGION THROUGH SOUTHERN NEW ENGLAND
Mesoscale Discussion 1825 NWS Storm Prediction Center Norman OK 1031 AM CDT Wed Aug 21 2019 Areas affected...Northern Mid Atlantic Coast region through southern New England Concerning...Severe potential...Watch possible Valid 211531Z - 211730Z Probability of Watch Issuance...60 percent SUMMARY...Intensifying thunderstorms posing a risk for potentially damaging wind gusts and, perhaps, an isolated tornado or two, appear increasingly possible by 2-4 PM EDT. This could require the issuance of one or two severe weather watches. DISCUSSION...Convective development appears to be undergoing at least some gradual intensification, within a narrow band now overspreading the Champlain and Hudson Valleys, and as far south as northern New Jersey. This appears to be occurring on the leading edge of mid-level forcing for ascent associated with a remnant convectively generated or enhanced perturbation, which is forecast to progress into and through western and northern New England by mid to late afternoon. This may be trailed to the southwest by another area of mid-level forcing for ascent spreading northeastward across the northern Mid Atlantic Coast region into southern New England. Based on latest observational data, seasonably moist boundary layer air may mostly remain confined to the south of a weak surface front, reinforced by rain-cooled air associated with weakening convection preceding the main ongoing band. This extends roughly from the leading edge of the convective band across northern Massachusetts, though this boundary could shift northward some into and through the afternoon. To the south of the front, insolation during the next few hours is expected to contribute to moderate mixed-layer CAPE of 1000-2000 J/kg, coincident with strengthening of west-southwesterly flow in the 700-500 mb layer. This may contribute to an environment increasingly conducive to organized convection by 18-20Z, which could include further intensification of the ongoing line and perhaps additional discrete storms, with supercell structures possible. Although low-level hodographs may be somewhat modest in size, a tornado or two might not be out of the question, mainly near the surface boundary across southern New England. Otherwise, strongest storms probably will pose a risk for potentially damaging wind gusts. ..Kerr/Guyer.. 08/21/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...GYX...BOX...BTV...OKX...ALY...PHI...BGM...CTP... LWX... LAT...LON 43597276 43207186 43187060 42567029 41777017 40667291 39807417 39187526 39897661 40957572 41367524 41547425 41877353 42307324 43597276 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Wed Aug 21 2019 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTHEAST... ...SUMMARY... The severe-thunderstorm threat appears most concentrated today over portions of the Northeast. ...Synopsis... In mid/upper levels, a relatively low-amplitude pattern will persist across most of the CONUS, with the main belt of westerlies covering about the northern 1/3 from the Pacific Northwest to New England. A synoptic-scale cyclone -- initially over northeastern ON and adjoining Hudson Bay waters -- will pivot slowly southeastward and eastward to nearby parts of QC through the period. An attendant positively tilted trough will move southeastward then eastward over the upper Great Lakes, followed by another, somewhat stronger trough across northern MN and Lake Superior late tonight. Downstream, a shortwave trough was evident in moisture-channel imagery across Lake Ontario, western NY, and the upper Ohio Valley. This feature will move eastward across the Mid-Atlantic region and New England through 03Z. In weaker westerlies aloft, MCVs and related vorticity lobes from prior overnight convection in the central Plains will move eastward over parts of the lower Missouri and mid Mississippi Valley regions today into this evening. At the surface, the 11Z analysis depicted a cold front from Lake Huron to central Lake Michigan, south-central IA, southeastern NE, northwestern KS, and portions of east-central/southeastern CO. By 00Z, this front should reach southeastern ON, southern Lower MI, north-central MO, central KS, to near the eastern CO/NM line. By 12Z the front should extend from northern NY to southwestern OH, southern IL, north-central/northeastern OK, the TX Panhandle, and northeastern NM. Over the central/southern Plains and mid Mississippi Valley, the front will be preceded by several convective outflow boundaries of variable baroclinicity. A warm front -- initially drawn near the southern New England coast and across southeastern NY/northeastern PA area -- will shift northeastward across much of the remainder of eastern NY and New England through the period. ...Northeast... Large-scale DCVA/ascent and warm advection, each preceding the aforementioned mid/upper-level shortwave trough, will spread over a favorably moist and destabilizing warm sector today in support of multiple rounds of convection, with sporadic damaging to severe gusts. Severe hail also is possible from the most intense/deepest cells, especially across portions of eastern NY and New England where the buoyancy/shear parameter space will best support organized multicells and isolated supercells within the convective regime. In addition to the influences aloft, low-level destabilization will occur as the warm-frontal zone moves northeastward, moisture advection occurs, and pockets of persistent diurnal heating occur around and between areas of antecedent cloud cover. These processes should result in preconvective MLCAPE commonly in the 1000-1500 J/KG range. In the absence of an EML or other mechanisms to support strong capping, MLCINH will weaken rapidly through the morning into midday, rendering a situation where only subtle boundary-layer forcing (e.g., surface heating, weak low-level convergence zones, outflow/differential-heating boundaries) will be needed to generate deep convection. In general, vertical shear should strengthen and instability will weaken with northward extent, though a broad area of overlap favorable for severe defines the 15%/slight-risk area. With somewhat backed low-level winds in the warm-frontal zone, and a southerly component just to its south in the warm sector, hodographs also may enlarge enough to yield isolated mesocyclones and a marginal tornado threat, generally overlapping the greatest hail potential, mainly over portions of New England. ...Central High Plains and Rockies/Foothills... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern WY across central/southern CO, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Midlevel flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ...KS/MO/IL... Isolated to numerous thunderstorms are possible this afternoon and evening along and ahead of the front, some of which may produce severe gusts and hail. Large areas of antecedent cloud cover and precip will disperse, but in doing so, will delay diurnal destabilization across much of KS/MO. Outflow and differential- heating boundaries left behind by this activity, and their intersection(s) with the frontal zone, should be primary foci for convective development and intensification this afternoon and evening. Where the boundary layer can heat well, and is relatively undisturbed by prior convective activity, steep lapse rates and surface dew points in the upper 60s to upper 70s F will support pockets of 3000-4000 J/kg MLCAPE, perhaps locally higher. Considerable uncertainties linger regarding the ultimate location, orientation and strength of the prefrontal boundaries. One or two relative concentrations of severe potential may develop as convection aggregates around areas of greatest diurnal destabilization and boundary-related forcing. However, mesoscale uncertainties preclude assigning any greater unconditional probabilities with the broader marginal risk, at this early juncture. Weak mid/upper-level winds, and related lack of more-robust deep shear, also will be limiting factors for a better-organized severe threat. ..Edwards/Dean.. 08/21/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Wed Aug 21 2019 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTHEAST... ...SUMMARY... The severe-thunderstorm threat appears most concentrated today over portions of the Northeast. ...Synopsis... In mid/upper levels, a relatively low-amplitude pattern will persist across most of the CONUS, with the main belt of westerlies covering about the northern 1/3 from the Pacific Northwest to New England. A synoptic-scale cyclone -- initially over northeastern ON and adjoining Hudson Bay waters -- will pivot slowly southeastward and eastward to nearby parts of QC through the period. An attendant positively tilted trough will move southeastward then eastward over the upper Great Lakes, followed by another, somewhat stronger trough across northern MN and Lake Superior late tonight. Downstream, a shortwave trough was evident in moisture-channel imagery across Lake Ontario, western NY, and the upper Ohio Valley. This feature will move eastward across the Mid-Atlantic region and New England through 03Z. In weaker westerlies aloft, MCVs and related vorticity lobes from prior overnight convection in the central Plains will move eastward over parts of the lower Missouri and mid Mississippi Valley regions today into this evening. At the surface, the 11Z analysis depicted a cold front from Lake Huron to central Lake Michigan, south-central IA, southeastern NE, northwestern KS, and portions of east-central/southeastern CO. By 00Z, this front should reach southeastern ON, southern Lower MI, north-central MO, central KS, to near the eastern CO/NM line. By 12Z the front should extend from northern NY to southwestern OH, southern IL, north-central/northeastern OK, the TX Panhandle, and northeastern NM. Over the central/southern Plains and mid Mississippi Valley, the front will be preceded by several convective outflow boundaries of variable baroclinicity. A warm front -- initially drawn near the southern New England coast and across southeastern NY/northeastern PA area -- will shift northeastward across much of the remainder of eastern NY and New England through the period. ...Northeast... Large-scale DCVA/ascent and warm advection, each preceding the aforementioned mid/upper-level shortwave trough, will spread over a favorably moist and destabilizing warm sector today in support of multiple rounds of convection, with sporadic damaging to severe gusts. Severe hail also is possible from the most intense/deepest cells, especially across portions of eastern NY and New England where the buoyancy/shear parameter space will best support organized multicells and isolated supercells within the convective regime. In addition to the influences aloft, low-level destabilization will occur as the warm-frontal zone moves northeastward, moisture advection occurs, and pockets of persistent diurnal heating occur around and between areas of antecedent cloud cover. These processes should result in preconvective MLCAPE commonly in the 1000-1500 J/KG range. In the absence of an EML or other mechanisms to support strong capping, MLCINH will weaken rapidly through the morning into midday, rendering a situation where only subtle boundary-layer forcing (e.g., surface heating, weak low-level convergence zones, outflow/differential-heating boundaries) will be needed to generate deep convection. In general, vertical shear should strengthen and instability will weaken with northward extent, though a broad area of overlap favorable for severe defines the 15%/slight-risk area. With somewhat backed low-level winds in the warm-frontal zone, and a southerly component just to its south in the warm sector, hodographs also may enlarge enough to yield isolated mesocyclones and a marginal tornado threat, generally overlapping the greatest hail potential, mainly over portions of New England. ...Central High Plains and Rockies/Foothills... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern WY across central/southern CO, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Midlevel flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ...KS/MO/IL... Isolated to numerous thunderstorms are possible this afternoon and evening along and ahead of the front, some of which may produce severe gusts and hail. Large areas of antecedent cloud cover and precip will disperse, but in doing so, will delay diurnal destabilization across much of KS/MO. Outflow and differential- heating boundaries left behind by this activity, and their intersection(s) with the frontal zone, should be primary foci for convective development and intensification this afternoon and evening. Where the boundary layer can heat well, and is relatively undisturbed by prior convective activity, steep lapse rates and surface dew points in the upper 60s to upper 70s F will support pockets of 3000-4000 J/kg MLCAPE, perhaps locally higher. Considerable uncertainties linger regarding the ultimate location, orientation and strength of the prefrontal boundaries. One or two relative concentrations of severe potential may develop as convection aggregates around areas of greatest diurnal destabilization and boundary-related forcing. However, mesoscale uncertainties preclude assigning any greater unconditional probabilities with the broader marginal risk, at this early juncture. Weak mid/upper-level winds, and related lack of more-robust deep shear, also will be limiting factors for a better-organized severe threat. ..Edwards/Dean.. 08/21/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Wed Aug 21 2019 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTHEAST... ...SUMMARY... The severe-thunderstorm threat appears most concentrated today over portions of the Northeast. ...Synopsis... In mid/upper levels, a relatively low-amplitude pattern will persist across most of the CONUS, with the main belt of westerlies covering about the northern 1/3 from the Pacific Northwest to New England. A synoptic-scale cyclone -- initially over northeastern ON and adjoining Hudson Bay waters -- will pivot slowly southeastward and eastward to nearby parts of QC through the period. An attendant positively tilted trough will move southeastward then eastward over the upper Great Lakes, followed by another, somewhat stronger trough across northern MN and Lake Superior late tonight. Downstream, a shortwave trough was evident in moisture-channel imagery across Lake Ontario, western NY, and the upper Ohio Valley. This feature will move eastward across the Mid-Atlantic region and New England through 03Z. In weaker westerlies aloft, MCVs and related vorticity lobes from prior overnight convection in the central Plains will move eastward over parts of the lower Missouri and mid Mississippi Valley regions today into this evening. At the surface, the 11Z analysis depicted a cold front from Lake Huron to central Lake Michigan, south-central IA, southeastern NE, northwestern KS, and portions of east-central/southeastern CO. By 00Z, this front should reach southeastern ON, southern Lower MI, north-central MO, central KS, to near the eastern CO/NM line. By 12Z the front should extend from northern NY to southwestern OH, southern IL, north-central/northeastern OK, the TX Panhandle, and northeastern NM. Over the central/southern Plains and mid Mississippi Valley, the front will be preceded by several convective outflow boundaries of variable baroclinicity. A warm front -- initially drawn near the southern New England coast and across southeastern NY/northeastern PA area -- will shift northeastward across much of the remainder of eastern NY and New England through the period. ...Northeast... Large-scale DCVA/ascent and warm advection, each preceding the aforementioned mid/upper-level shortwave trough, will spread over a favorably moist and destabilizing warm sector today in support of multiple rounds of convection, with sporadic damaging to severe gusts. Severe hail also is possible from the most intense/deepest cells, especially across portions of eastern NY and New England where the buoyancy/shear parameter space will best support organized multicells and isolated supercells within the convective regime. In addition to the influences aloft, low-level destabilization will occur as the warm-frontal zone moves northeastward, moisture advection occurs, and pockets of persistent diurnal heating occur around and between areas of antecedent cloud cover. These processes should result in preconvective MLCAPE commonly in the 1000-1500 J/KG range. In the absence of an EML or other mechanisms to support strong capping, MLCINH will weaken rapidly through the morning into midday, rendering a situation where only subtle boundary-layer forcing (e.g., surface heating, weak low-level convergence zones, outflow/differential-heating boundaries) will be needed to generate deep convection. In general, vertical shear should strengthen and instability will weaken with northward extent, though a broad area of overlap favorable for severe defines the 15%/slight-risk area. With somewhat backed low-level winds in the warm-frontal zone, and a southerly component just to its south in the warm sector, hodographs also may enlarge enough to yield isolated mesocyclones and a marginal tornado threat, generally overlapping the greatest hail potential, mainly over portions of New England. ...Central High Plains and Rockies/Foothills... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern WY across central/southern CO, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Midlevel flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ...KS/MO/IL... Isolated to numerous thunderstorms are possible this afternoon and evening along and ahead of the front, some of which may produce severe gusts and hail. Large areas of antecedent cloud cover and precip will disperse, but in doing so, will delay diurnal destabilization across much of KS/MO. Outflow and differential- heating boundaries left behind by this activity, and their intersection(s) with the frontal zone, should be primary foci for convective development and intensification this afternoon and evening. Where the boundary layer can heat well, and is relatively undisturbed by prior convective activity, steep lapse rates and surface dew points in the upper 60s to upper 70s F will support pockets of 3000-4000 J/kg MLCAPE, perhaps locally higher. Considerable uncertainties linger regarding the ultimate location, orientation and strength of the prefrontal boundaries. One or two relative concentrations of severe potential may develop as convection aggregates around areas of greatest diurnal destabilization and boundary-related forcing. However, mesoscale uncertainties preclude assigning any greater unconditional probabilities with the broader marginal risk, at this early juncture. Weak mid/upper-level winds, and related lack of more-robust deep shear, also will be limiting factors for a better-organized severe threat. ..Edwards/Dean.. 08/21/2019 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Wed Aug 21 2019 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTHEAST... ...SUMMARY... The severe-thunderstorm threat appears most concentrated today over portions of the Northeast. ...Synopsis... In mid/upper levels, a relatively low-amplitude pattern will persist across most of the CONUS, with the main belt of westerlies covering about the northern 1/3 from the Pacific Northwest to New England. A synoptic-scale cyclone -- initially over northeastern ON and adjoining Hudson Bay waters -- will pivot slowly southeastward and eastward to nearby parts of QC through the period. An attendant positively tilted trough will move southeastward then eastward over the upper Great Lakes, followed by another, somewhat stronger trough across northern MN and Lake Superior late tonight. Downstream, a shortwave trough was evident in moisture-channel imagery across Lake Ontario, western NY, and the upper Ohio Valley. This feature will move eastward across the Mid-Atlantic region and New England through 03Z. In weaker westerlies aloft, MCVs and related vorticity lobes from prior overnight convection in the central Plains will move eastward over parts of the lower Missouri and mid Mississippi Valley regions today into this evening. At the surface, the 11Z analysis depicted a cold front from Lake Huron to central Lake Michigan, south-central IA, southeastern NE, northwestern KS, and portions of east-central/southeastern CO. By 00Z, this front should reach southeastern ON, southern Lower MI, north-central MO, central KS, to near the eastern CO/NM line. By 12Z the front should extend from northern NY to southwestern OH, southern IL, north-central/northeastern OK, the TX Panhandle, and northeastern NM. Over the central/southern Plains and mid Mississippi Valley, the front will be preceded by several convective outflow boundaries of variable baroclinicity. A warm front -- initially drawn near the southern New England coast and across southeastern NY/northeastern PA area -- will shift northeastward across much of the remainder of eastern NY and New England through the period. ...Northeast... Large-scale DCVA/ascent and warm advection, each preceding the aforementioned mid/upper-level shortwave trough, will spread over a favorably moist and destabilizing warm sector today in support of multiple rounds of convection, with sporadic damaging to severe gusts. Severe hail also is possible from the most intense/deepest cells, especially across portions of eastern NY and New England where the buoyancy/shear parameter space will best support organized multicells and isolated supercells within the convective regime. In addition to the influences aloft, low-level destabilization will occur as the warm-frontal zone moves northeastward, moisture advection occurs, and pockets of persistent diurnal heating occur around and between areas of antecedent cloud cover. These processes should result in preconvective MLCAPE commonly in the 1000-1500 J/KG range. In the absence of an EML or other mechanisms to support strong capping, MLCINH will weaken rapidly through the morning into midday, rendering a situation where only subtle boundary-layer forcing (e.g., surface heating, weak low-level convergence zones, outflow/differential-heating boundaries) will be needed to generate deep convection. In general, vertical shear should strengthen and instability will weaken with northward extent, though a broad area of overlap favorable for severe defines the 15%/slight-risk area. With somewhat backed low-level winds in the warm-frontal zone, and a southerly component just to its south in the warm sector, hodographs also may enlarge enough to yield isolated mesocyclones and a marginal tornado threat, generally overlapping the greatest hail potential, mainly over portions of New England. ...Central High Plains and Rockies/Foothills... Isolated to widely scattered thunderstorms should develop this afternoon over the eastern mountains and foothills from northern WY across central/southern CO, offering the potential for isolated severe hail and gusts. Activity is expected predominantly in the post-frontal/upslope region where lift is maximized by a combination of upslope flow and diabatic surface heating of the higher terrain (minimizing MLCINH). Midlevel flow is forecast to be modest; however, vertical shear will be stronger than over lower elevations ahead of the front because of the backed boundary-layer winds and relatively extended low-level hodographs. As such, a mixture of supercellular and multicellular structures are possible. ...KS/MO/IL... Isolated to numerous thunderstorms are possible this afternoon and evening along and ahead of the front, some of which may produce severe gusts and hail. Large areas of antecedent cloud cover and precip will disperse, but in doing so, will delay diurnal destabilization across much of KS/MO. Outflow and differential- heating boundaries left behind by this activity, and their intersection(s) with the frontal zone, should be primary foci for convective development and intensification this afternoon and evening. Where the boundary layer can heat well, and is relatively undisturbed by prior convective activity, steep lapse rates and surface dew points in the upper 60s to upper 70s F will support pockets of 3000-4000 J/kg MLCAPE, perhaps locally higher. Considerable uncertainties linger regarding the ultimate location, orientation and strength of the prefrontal boundaries. One or two relative concentrations of severe potential may develop as convection aggregates around areas of greatest diurnal destabilization and boundary-related forcing. However, mesoscale uncertainties preclude assigning any greater unconditional probabilities with the broader marginal risk, at this early juncture. Weak mid/upper-level winds, and related lack of more-robust deep shear, also will be limiting factors for a better-organized severe threat. ..Edwards/Dean.. 08/21/2019 Read more

WW 0608 Status Updates
STATUS REPORT ON WW 608 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 40 NE MCK TO 10 WNW ANW. WW 608 WILL BE ALLOWED TO EXPIRE AT 211100Z. ..DEAN..08/21/19 ATTN...WFO...LBF...CYS... STATUS REPORT FOR WS 608 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS NEC009-017-041-115-211100- NE . NEBRASKA COUNTIES INCLUDED ARE BLAINE BROWN CUSTER LOUP 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 CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 608 SEVERE TSTM NE 210500Z - 211100Z
URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 608 NWS Storm Prediction Center Norman OK 1100 PM MDT Tue Aug 20 2019 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Western and central Nebraska * Effective this Tuesday night and Wednesday morning from 1100 PM until 500 AM MDT. * 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 SUMMARY...Line of strong to isolated severe storms may persist east into central Nebraska through the pre-dawn hours. The severe thunderstorm watch area is approximately along and 50 statute miles north and south of a line from 40 miles west southwest of Alliance NE to 15 miles north northeast of Broken Bow NE. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU8). 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 607... 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 27025. ...Grams Read more

WW 0608 Status Updates
STATUS REPORT ON WW 608 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 30 E IML TO LBF TO 25 N LBF TO MHN TO 25 SSW VTN. FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1824 ..DEAN..08/21/19 ATTN...WFO...LBF...CYS... STATUS REPORT FOR WS 608 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS NEC009-017-031-041-091-111-113-115-117-171-211040- NE . NEBRASKA COUNTIES INCLUDED ARE BLAINE BROWN CHERRY CUSTER HOOKER LINCOLN LOGAN LOUP MCPHERSON THOMAS 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 CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0316 AM CDT Wed Aug 21 2019 Valid 241200Z - 291200Z ...DISCUSSION... Strong northwest winds aloft will dive southeastward across the northern Rockies and into the Plains, with one or more leading waves affecting the northern Plains on Saturday/D4 and Sunday/D5 before the larger amplification occurs Tuesday/D7 into Wednesday/D8. These lead waves will interact with a plume of mid 60s F dewpoints over the Dakotas and western MN D4 and D5, with at least isolated severe hail possible. Mitigating severe coverage will be relatively cool air emanating out of a surface ridge to the east, suggesting storms may become elevated as they move east away from the deeply mixed air near the surface trough. That said, models differ on the timing of these waves, thus predictability is too low to introduce severe probabilities. During the D6-D8 time frame, more robust low-level moisture will be in place from NE toward the Upper Great Lakes, and winds aloft will increase over the northern Plains, Upper MS Valley and Great Lakes, suggesting severe potential. Though timing issues exist amongst the models, the general signal is for the upper winds to become nearly parallel to the cold front, with areas of damaging wind possible from the central and northern Plains to the Upper MS Valley and Midwest. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0316 AM CDT Wed Aug 21 2019 Valid 241200Z - 291200Z ...DISCUSSION... Strong northwest winds aloft will dive southeastward across the northern Rockies and into the Plains, with one or more leading waves affecting the northern Plains on Saturday/D4 and Sunday/D5 before the larger amplification occurs Tuesday/D7 into Wednesday/D8. These lead waves will interact with a plume of mid 60s F dewpoints over the Dakotas and western MN D4 and D5, with at least isolated severe hail possible. Mitigating severe coverage will be relatively cool air emanating out of a surface ridge to the east, suggesting storms may become elevated as they move east away from the deeply mixed air near the surface trough. That said, models differ on the timing of these waves, thus predictability is too low to introduce severe probabilities. During the D6-D8 time frame, more robust low-level moisture will be in place from NE toward the Upper Great Lakes, and winds aloft will increase over the northern Plains, Upper MS Valley and Great Lakes, suggesting severe potential. Though timing issues exist amongst the models, the general signal is for the upper winds to become nearly parallel to the cold front, with areas of damaging wind possible from the central and northern Plains to the Upper MS Valley and Midwest. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0316 AM CDT Wed Aug 21 2019 Valid 241200Z - 291200Z ...DISCUSSION... Strong northwest winds aloft will dive southeastward across the northern Rockies and into the Plains, with one or more leading waves affecting the northern Plains on Saturday/D4 and Sunday/D5 before the larger amplification occurs Tuesday/D7 into Wednesday/D8. These lead waves will interact with a plume of mid 60s F dewpoints over the Dakotas and western MN D4 and D5, with at least isolated severe hail possible. Mitigating severe coverage will be relatively cool air emanating out of a surface ridge to the east, suggesting storms may become elevated as they move east away from the deeply mixed air near the surface trough. That said, models differ on the timing of these waves, thus predictability is too low to introduce severe probabilities. During the D6-D8 time frame, more robust low-level moisture will be in place from NE toward the Upper Great Lakes, and winds aloft will increase over the northern Plains, Upper MS Valley and Great Lakes, suggesting severe potential. Though timing issues exist amongst the models, the general signal is for the upper winds to become nearly parallel to the cold front, with areas of damaging wind possible from the central and northern Plains to the Upper MS Valley and Midwest. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0316 AM CDT Wed Aug 21 2019 Valid 241200Z - 291200Z ...DISCUSSION... Strong northwest winds aloft will dive southeastward across the northern Rockies and into the Plains, with one or more leading waves affecting the northern Plains on Saturday/D4 and Sunday/D5 before the larger amplification occurs Tuesday/D7 into Wednesday/D8. These lead waves will interact with a plume of mid 60s F dewpoints over the Dakotas and western MN D4 and D5, with at least isolated severe hail possible. Mitigating severe coverage will be relatively cool air emanating out of a surface ridge to the east, suggesting storms may become elevated as they move east away from the deeply mixed air near the surface trough. That said, models differ on the timing of these waves, thus predictability is too low to introduce severe probabilities. During the D6-D8 time frame, more robust low-level moisture will be in place from NE toward the Upper Great Lakes, and winds aloft will increase over the northern Plains, Upper MS Valley and Great Lakes, suggesting severe potential. Though timing issues exist amongst the models, the general signal is for the upper winds to become nearly parallel to the cold front, with areas of damaging wind possible from the central and northern Plains to the Upper MS Valley and Midwest. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0316 AM CDT Wed Aug 21 2019 Valid 241200Z - 291200Z ...DISCUSSION... Strong northwest winds aloft will dive southeastward across the northern Rockies and into the Plains, with one or more leading waves affecting the northern Plains on Saturday/D4 and Sunday/D5 before the larger amplification occurs Tuesday/D7 into Wednesday/D8. These lead waves will interact with a plume of mid 60s F dewpoints over the Dakotas and western MN D4 and D5, with at least isolated severe hail possible. Mitigating severe coverage will be relatively cool air emanating out of a surface ridge to the east, suggesting storms may become elevated as they move east away from the deeply mixed air near the surface trough. That said, models differ on the timing of these waves, thus predictability is too low to introduce severe probabilities. During the D6-D8 time frame, more robust low-level moisture will be in place from NE toward the Upper Great Lakes, and winds aloft will increase over the northern Plains, Upper MS Valley and Great Lakes, suggesting severe potential. Though timing issues exist amongst the models, the general signal is for the upper winds to become nearly parallel to the cold front, with areas of damaging wind possible from the central and northern Plains to the Upper MS Valley and Midwest. Read more

MD 1824 CONCERNING SEVERE THUNDERSTORM WATCH 608... FOR WESTERN/CENTRAL NE
Mesoscale Discussion 1824 NWS Storm Prediction Center Norman OK 0315 AM CDT Wed Aug 21 2019 Areas affected...Western/central NE Concerning...Severe Thunderstorm Watch 608... Valid 210815Z - 210945Z The severe weather threat for Severe Thunderstorm Watch 608 continues. SUMMARY...Some severe wind risk will continue with bow echo moving across western Nebraska. Gradual weakening is expected with time, and downstream watch issuance is unlikely. DISCUSSION...A bow echo is moving eastward out of the NE Panhandle as of 08Z, with increasingly disorganized elevated convection ongoing downstream into central NE. Relatively steep pressure rises and cold temperatures (falling into the 50s F) in the wake of the bow suggest a somewhat well-organized cold pool, though radar velocities indicate that the rear-inflow jet is not overly strong, and observed wind speeds (where available) have been subsevere over the last 1-2 hours. While the airmass immediately downstream of the bow likely remains strongly unstable (MUCAPE of around 3000 J/kg), convectively overturned air emanating out of western KS and also central NE is likely to erode this instability with time, resulting in a general weakening trend. Some severe wind risk will persist given the well-established cold pool, but a general decrease in the wind risk is expected with eastward extent. With these factors in mind, downstream watch issuance into central NE is unlikely. ..Dean/Edwards.. 08/21/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...GID...LBF... LAT...LON 42170210 42270103 41739899 41319816 40609818 40419843 40359896 40369949 40419997 40460068 40820154 41160159 41370162 41670177 42010217 42170210 Read more

WW 0608 Status Updates
STATUS REPORT ON WW 608 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 45 WSW SNY TO 10 ENE SNY TO 40 ENE SNY TO 40 SE AIA TO 5 E AIA TO 60 NE AIA. ..DEAN..08/21/19 ATTN...WFO...LBF...CYS... STATUS REPORT FOR WS 608 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS NEC005-009-017-031-033-041-049-069-075-091-101-111-113-115-117- 135-161-171-210840- NE . NEBRASKA COUNTIES INCLUDED ARE ARTHUR BLAINE BROWN CHERRY CHEYENNE CUSTER DEUEL GARDEN GRANT HOOKER KEITH LINCOLN LOGAN LOUP MCPHERSON PERKINS SHERIDAN THOMAS 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 CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more