SPC Nov 21, 2023 1630 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1028 AM CST Tue Nov 21 2023 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN/CENTRAL ALABAMA...THE FLORIDA PANHANDLE...AND SOUTHWESTERN GEORGIA... ...SUMMARY... A few tornadoes and isolated damaging gusts still appear possible today across parts of southern Alabama, southwestern Georgia, and the Florida Panhandle. Isolated damaging gusts and perhaps a tornado also remain possible this afternoon through tonight from central/northern Georgia into the Carolinas and southeastern Virginia. ...Synopsis... A large mid/upper-level cyclone over the Great Lakes this morning will continue to move eastward today. A trailing, positively tilted upper trough extends across the Midwest into the mid/lower MS Valley and southern Plains. The primary surface low over the Midwest is also forecast to develop slowly east-northeastward toward the Lower Great Lakes through tonight. A trailing cold front will progress eastward today and tonight across the Southeast and Mid-Atlantic states as a secondary surface low eventually forms over VA/MD and develops quickly northeastward across the coastal Mid-Atlantic. ...Central to Northeast Gulf Coast States... Swaths of warm-advection-related precipitation and widespread cloud cover have hindered daytime heating so far this morning across southern AL, the FL Panhandle, and GA. Still, some clearing has recently been noted between the cold front ongoing precipitation. Most guidance suggests that surface temperatures reaching into the low 70s will be needed for sufficient boundary-layer destabilization to support surface-based thunderstorms. Even with this modest heating, poor lapse rates aloft will likely hinder the degree of MLCAPE across the warm sector this afternoon. This should temper updraft intensities to some extent. But, latest VWPs from area radars show rather strong low-level and deep-layer shear are still present across this region. Any robust convection that can develop along/near the cold front this afternoon could become supercellular, with an associated threat for a few tornadoes and isolated damaging winds. But, confidence remains low that enough instability will develop to support intense thunderstorms. Have therefore maintained the low-confidence Slight Risk across this region with minimal changes. ...Georgia into the Carolinas and Southeastern Virginia... Widespread cloud cover and areas of precipitation remain prevalent from GA into the NC/SC and VA, with a warm front/retreating wedge front delineating the northern extent of low-level moisture return. Instability should remain fairly weak through the period with northeastward extent from central/northern GA into the Carolinas. This limits confidence in thunderstorm intensities this afternoon. Still, a conditional threat for damaging wind gusts and perhaps a tornado or two exists with mainly linear convection that can develop/strengthen along the eastward-moving cold front this afternoon and evening. Late tonight, a low-topped line of convection may develop along the front from NC into southeastern VA and vicinity. While instability is forecast to remain minimal, strong flow at low/mid levels may still reach the surface through convective downdrafts. Have expanded the Marginal Risk for isolated damaging winds northward a bit based on this potential. Confidence in supercells developing across coastal/eastern NC in the last few hours of the period remains low. ..Gleason/Moore.. 11/21/2023 Read more

SPC Nov 21, 2023 1630 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1028 AM CST Tue Nov 21 2023 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN/CENTRAL ALABAMA...THE FLORIDA PANHANDLE...AND SOUTHWESTERN GEORGIA... ...SUMMARY... A few tornadoes and isolated damaging gusts still appear possible today across parts of southern Alabama, southwestern Georgia, and the Florida Panhandle. Isolated damaging gusts and perhaps a tornado also remain possible this afternoon through tonight from central/northern Georgia into the Carolinas and southeastern Virginia. ...Synopsis... A large mid/upper-level cyclone over the Great Lakes this morning will continue to move eastward today. A trailing, positively tilted upper trough extends across the Midwest into the mid/lower MS Valley and southern Plains. The primary surface low over the Midwest is also forecast to develop slowly east-northeastward toward the Lower Great Lakes through tonight. A trailing cold front will progress eastward today and tonight across the Southeast and Mid-Atlantic states as a secondary surface low eventually forms over VA/MD and develops quickly northeastward across the coastal Mid-Atlantic. ...Central to Northeast Gulf Coast States... Swaths of warm-advection-related precipitation and widespread cloud cover have hindered daytime heating so far this morning across southern AL, the FL Panhandle, and GA. Still, some clearing has recently been noted between the cold front ongoing precipitation. Most guidance suggests that surface temperatures reaching into the low 70s will be needed for sufficient boundary-layer destabilization to support surface-based thunderstorms. Even with this modest heating, poor lapse rates aloft will likely hinder the degree of MLCAPE across the warm sector this afternoon. This should temper updraft intensities to some extent. But, latest VWPs from area radars show rather strong low-level and deep-layer shear are still present across this region. Any robust convection that can develop along/near the cold front this afternoon could become supercellular, with an associated threat for a few tornadoes and isolated damaging winds. But, confidence remains low that enough instability will develop to support intense thunderstorms. Have therefore maintained the low-confidence Slight Risk across this region with minimal changes. ...Georgia into the Carolinas and Southeastern Virginia... Widespread cloud cover and areas of precipitation remain prevalent from GA into the NC/SC and VA, with a warm front/retreating wedge front delineating the northern extent of low-level moisture return. Instability should remain fairly weak through the period with northeastward extent from central/northern GA into the Carolinas. This limits confidence in thunderstorm intensities this afternoon. Still, a conditional threat for damaging wind gusts and perhaps a tornado or two exists with mainly linear convection that can develop/strengthen along the eastward-moving cold front this afternoon and evening. Late tonight, a low-topped line of convection may develop along the front from NC into southeastern VA and vicinity. While instability is forecast to remain minimal, strong flow at low/mid levels may still reach the surface through convective downdrafts. Have expanded the Marginal Risk for isolated damaging winds northward a bit based on this potential. Confidence in supercells developing across coastal/eastern NC in the last few hours of the period remains low. ..Gleason/Moore.. 11/21/2023 Read more

SPC Nov 21, 2023 1630 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1028 AM CST Tue Nov 21 2023 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN/CENTRAL ALABAMA...THE FLORIDA PANHANDLE...AND SOUTHWESTERN GEORGIA... ...SUMMARY... A few tornadoes and isolated damaging gusts still appear possible today across parts of southern Alabama, southwestern Georgia, and the Florida Panhandle. Isolated damaging gusts and perhaps a tornado also remain possible this afternoon through tonight from central/northern Georgia into the Carolinas and southeastern Virginia. ...Synopsis... A large mid/upper-level cyclone over the Great Lakes this morning will continue to move eastward today. A trailing, positively tilted upper trough extends across the Midwest into the mid/lower MS Valley and southern Plains. The primary surface low over the Midwest is also forecast to develop slowly east-northeastward toward the Lower Great Lakes through tonight. A trailing cold front will progress eastward today and tonight across the Southeast and Mid-Atlantic states as a secondary surface low eventually forms over VA/MD and develops quickly northeastward across the coastal Mid-Atlantic. ...Central to Northeast Gulf Coast States... Swaths of warm-advection-related precipitation and widespread cloud cover have hindered daytime heating so far this morning across southern AL, the FL Panhandle, and GA. Still, some clearing has recently been noted between the cold front ongoing precipitation. Most guidance suggests that surface temperatures reaching into the low 70s will be needed for sufficient boundary-layer destabilization to support surface-based thunderstorms. Even with this modest heating, poor lapse rates aloft will likely hinder the degree of MLCAPE across the warm sector this afternoon. This should temper updraft intensities to some extent. But, latest VWPs from area radars show rather strong low-level and deep-layer shear are still present across this region. Any robust convection that can develop along/near the cold front this afternoon could become supercellular, with an associated threat for a few tornadoes and isolated damaging winds. But, confidence remains low that enough instability will develop to support intense thunderstorms. Have therefore maintained the low-confidence Slight Risk across this region with minimal changes. ...Georgia into the Carolinas and Southeastern Virginia... Widespread cloud cover and areas of precipitation remain prevalent from GA into the NC/SC and VA, with a warm front/retreating wedge front delineating the northern extent of low-level moisture return. Instability should remain fairly weak through the period with northeastward extent from central/northern GA into the Carolinas. This limits confidence in thunderstorm intensities this afternoon. Still, a conditional threat for damaging wind gusts and perhaps a tornado or two exists with mainly linear convection that can develop/strengthen along the eastward-moving cold front this afternoon and evening. Late tonight, a low-topped line of convection may develop along the front from NC into southeastern VA and vicinity. While instability is forecast to remain minimal, strong flow at low/mid levels may still reach the surface through convective downdrafts. Have expanded the Marginal Risk for isolated damaging winds northward a bit based on this potential. Confidence in supercells developing across coastal/eastern NC in the last few hours of the period remains low. ..Gleason/Moore.. 11/21/2023 Read more

SPC Nov 21, 2023 1630 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1028 AM CST Tue Nov 21 2023 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHERN/CENTRAL ALABAMA...THE FLORIDA PANHANDLE...AND SOUTHWESTERN GEORGIA... ...SUMMARY... A few tornadoes and isolated damaging gusts still appear possible today across parts of southern Alabama, southwestern Georgia, and the Florida Panhandle. Isolated damaging gusts and perhaps a tornado also remain possible this afternoon through tonight from central/northern Georgia into the Carolinas and southeastern Virginia. ...Synopsis... A large mid/upper-level cyclone over the Great Lakes this morning will continue to move eastward today. A trailing, positively tilted upper trough extends across the Midwest into the mid/lower MS Valley and southern Plains. The primary surface low over the Midwest is also forecast to develop slowly east-northeastward toward the Lower Great Lakes through tonight. A trailing cold front will progress eastward today and tonight across the Southeast and Mid-Atlantic states as a secondary surface low eventually forms over VA/MD and develops quickly northeastward across the coastal Mid-Atlantic. ...Central to Northeast Gulf Coast States... Swaths of warm-advection-related precipitation and widespread cloud cover have hindered daytime heating so far this morning across southern AL, the FL Panhandle, and GA. Still, some clearing has recently been noted between the cold front ongoing precipitation. Most guidance suggests that surface temperatures reaching into the low 70s will be needed for sufficient boundary-layer destabilization to support surface-based thunderstorms. Even with this modest heating, poor lapse rates aloft will likely hinder the degree of MLCAPE across the warm sector this afternoon. This should temper updraft intensities to some extent. But, latest VWPs from area radars show rather strong low-level and deep-layer shear are still present across this region. Any robust convection that can develop along/near the cold front this afternoon could become supercellular, with an associated threat for a few tornadoes and isolated damaging winds. But, confidence remains low that enough instability will develop to support intense thunderstorms. Have therefore maintained the low-confidence Slight Risk across this region with minimal changes. ...Georgia into the Carolinas and Southeastern Virginia... Widespread cloud cover and areas of precipitation remain prevalent from GA into the NC/SC and VA, with a warm front/retreating wedge front delineating the northern extent of low-level moisture return. Instability should remain fairly weak through the period with northeastward extent from central/northern GA into the Carolinas. This limits confidence in thunderstorm intensities this afternoon. Still, a conditional threat for damaging wind gusts and perhaps a tornado or two exists with mainly linear convection that can develop/strengthen along the eastward-moving cold front this afternoon and evening. Late tonight, a low-topped line of convection may develop along the front from NC into southeastern VA and vicinity. While instability is forecast to remain minimal, strong flow at low/mid levels may still reach the surface through convective downdrafts. Have expanded the Marginal Risk for isolated damaging winds northward a bit based on this potential. Confidence in supercells developing across coastal/eastern NC in the last few hours of the period remains low. ..Gleason/Moore.. 11/21/2023 Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook

1 year 8 months ago
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1006 AM CST Tue Nov 21 2023 Valid 211700Z - 221200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 11/21/2023 .PREV DISCUSSION... /ISSUED 0143 AM CST Tue Nov 21 2023/ ...Synopsis... Across the CONUS, the mid-level flow pattern should continue to amplify as broad troughing over the central CONUS slides eastward. At the same time, ridging will intensify over the West Coast as strong surface high pressure develops over the Pacific Northwest and northern Great Basin. Offshore flow will continue over parts of southern CA for the first half of the period, before weakening as the high pressure moves toward the Plains. Dry northerly winds are also expected over much of the central and southern High Plains. However, with limited fuels owing to cooler temperatures and recent precipitation, fire-weather concerns are expected to remain localized. Weak low pressure and a cold front will bring much cooler temperatures and widespread precipitation to the eastern US, limiting the fire-weather threat. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 1300 UTC Day 1 Convective Outlook

1 year 8 months ago
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0634 AM CST Tue Nov 21 2023 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ALABAMA...SOUTHWESTERN GEORGIA AND PARTS OF THE FLORIDA PANHANDLE... ...SUMMARY... A few tornadoes and isolated damaging gusts are possible today across southern Alabama, southwestern Georgia and parts of the Florida Panhandle. Isolated damaging gusts are possible, along with a marginal tornado threat, from there northeastward to the coastal Carolinas. ...Synopsis... In mid/upper levels, a split-flow pattern will develop this period, as a strong shortwave trough now over northwestern MX digs southeastward and evolves into a cut-off cyclone, centered over Sinaloa at 12Z tomorrow. Meanwhile, moisture-channel imagery indicates a vorticity max and formerly closed circulation over northern IL, on the northern part of a trough extending southwestward to southwest TX. Though now in phase with the MX perturbation, the IL one will break northeastward across the Lower Great Lakes, ahead of an amplifying shortwave trough now over MN. The MN feature will dig southward to the Ozarks today, then pivot eastward across the Mid-South and lower Mississippi Valley tonight as a closed (or very nearly closed) 500-mb low. Ahead of all that, and the associated mean trough, a broad belt of southwest flow aloft will shift slowly eastward with height falls over parts of the Southeast and southern Atlantic Coast. The 11Z surface analysis showed a primary synoptic low -- associated with the IL mid/upper perturbation. The associated cold front was analyzed near LAF. A cold front was moving southeastward over eastern/southern MS, southeastern LA, and the northwestern Gulf. A warm/marine front was drawn from a secondary/triple-point low near CBM southeastward across the PNS area and northeastern Gulf, becoming quasistationary near the southwest coastline of Florida. The warm front is forecast to shift diffusely northeastward across eastern AL, southern/eastern GA and parts of the Carolinas through the period, while being overtaken from north-south by a belt of precip/thunderstorms. The cold front is forecast to move eastward/southeastward by 00Z to the Appalachians of western VA/NC/SC and northern GA, southwestward over southeastern AL, the west-central FL Panhandle and central Gulf. Overnight cyclogenesis should occur along this boundary, moving northeastward up the Atlantic Seaboard, with the surface low over NJ by 12Z. The cold front should extend southwestward across eastern NC -- where early-stage/secondary frontal-wave low development is possible ahead of the Mid-South shortwave perturbation. The front then should extend from there across northern FL to the south-central Gulf. ...Northeastern Gulf Coastal Plain... An ongoing, rather nebulously organized swath of precip and isolated embedded thunderstorms is apparent from near the mouth of the Mississippi River northeastward across parts of southern/eastern AL, the FL Panhandle and western GA. Within or behind this activity, diurnal destabilization and low-level convergence should support reorganization of the convective belt today, and especially from midday through afternoon. This may come about as convection forming nearer to the front moves eastward and merges with what is left of the ongoing belt. Either way, a better-focused corridor of thunderstorms is expected to take shape over parts of AL and the FL Panhandle and move eastward, while the warm front diffusely shifts inland, and moisture transport and theta-e advection continue from the Gulf. Forecast soundings today suggest a plume of 500-1200 J/kg MLCAPE within about 100 nm of the coast, weakening/narrowing northward. Before prefrontal flow veers to southwesterly, southerlies are expected through much of the boundary layer, veering with height above about 1 km, and contributing to large hodographs. Around 150-300 J/kg effective SRH may develop, about 75-150 J/kg of which is in the lowest 500 m. The associated parameter space should support some tornado potential with any sustained supercells or the strongest line-embedded mesovortices. ...Remainder of GA-Carolinas... The main band of convection should extend from the Gulf Coastal Plain northward into the southern Appalachians by mid/late afternoon, the move eastward over more of GA/SC this evening into tonight. Already modest buoyancy should diminishing northward and with time for the most part, given less-unstable low-level trajectories apparent in progs out of the northern FL Peninsula. Large-scale forcing should weaken as the Great Lakes-area trough aloft shifts away from the region, with mid/upper flow largely parallel to the swath of low-level lift supporting the convection. Yet favorable low-level and deep shear will persist. As such, a more conditional and isolated severe potential is apparent northeast of the 15%/"slight risk" area. Though presently remaining in the range of unconditional marginal probabilities, a secondary/conditional ramp-up in severe threat may develop late tonight across eastern/coastal NC. Sufficient southerly flow component in the lower boundary layer should be maintained to yield a persistent fetch off warm Atlantic waters -- and especially if the frontal-wave development is a bit stronger than currently forecast. This should yield a corridor of mid-60s F surface dewpoints over eastern NC the last several hours of the period, and perhaps mid/upper 60s along the immediate coast. That should offset weak, nearly moist-adiabatic deep-layer lapse rates enough to yield 300-800 J/kg MLCAPE. Shear will favor embedded supercells and/or mesovortices with the main line, as well as storm-scale rotation for some cells ahead of it moving off the ocean. Forecast soundings generally depict about 30-40 kt effective-shear magnitudes, and long lowest-km hodographs beneath a 50+ kt LLJ. At this time, weak instability and uncertainty on coverage of favorable storm mode precludes higher probabilities. ..Edwards/Leitman.. 11/21/2023 Read more

SPC Nov 21, 2023 Day 4-8 Severe Weather Outlook

1 year 8 months ago
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0314 AM CST Tue Nov 21 2023 Valid 241200Z - 291200Z ...DISCUSSION... Severe-thunderstorm potential still appears limited through the extended range. While the typical spread is noted regarding synoptic-scale details, guidance generally depicts the persistence of broad upper-level troughing over most of the CONUS, with periodic cold frontal passages tending to limit inland moisture transport from the Gulf of Mexico. Frontal wave development still appears possible on D4/Friday across the Gulf of Mexico, which would move eastward and bring some thunderstorm potential into parts of the FL Peninsula. However, with limited upper-level support, this development is expected to remain weak, and the potential for organized convection currently appears limited. Richer low-level moisture may return to areas near the TX Gulf Coast over the weekend, in response to a deep upper-level trough approaching the central CONUS. However, stronger large-scale ascent will likely be displaced well north of the warm front, with only weak surface low development expected near deep south TX before the next cold front surges southward early next week. Read more

SPC Nov 21, 2023 Day 4-8 Severe Weather Outlook

1 year 8 months ago
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0314 AM CST Tue Nov 21 2023 Valid 241200Z - 291200Z ...DISCUSSION... Severe-thunderstorm potential still appears limited through the extended range. While the typical spread is noted regarding synoptic-scale details, guidance generally depicts the persistence of broad upper-level troughing over most of the CONUS, with periodic cold frontal passages tending to limit inland moisture transport from the Gulf of Mexico. Frontal wave development still appears possible on D4/Friday across the Gulf of Mexico, which would move eastward and bring some thunderstorm potential into parts of the FL Peninsula. However, with limited upper-level support, this development is expected to remain weak, and the potential for organized convection currently appears limited. Richer low-level moisture may return to areas near the TX Gulf Coast over the weekend, in response to a deep upper-level trough approaching the central CONUS. However, stronger large-scale ascent will likely be displaced well north of the warm front, with only weak surface low development expected near deep south TX before the next cold front surges southward early next week. Read more