Severe Storms

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CST Sat Dec 14 2024 Valid 141700Z - 151200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 12/14/2024 .PREV DISCUSSION... /ISSUED 0200 AM CST Sat Dec 14 2024/ ...Synopsis... A progressive mid-level trough moving over the Southern Plains will rapidly move eastward as shortwave ridging develops over the Rockies and High Plains in its wake. A second mid-level trough farther west will begin to approach later this evening and overnight as increasingly strong westerly flow overspreads the Plains again. The ridging will initially favor weak surface winds and relatively mild temperatures through much of the day before the approaching trough aids in developing a lee cyclone over the central and northern High Plains. The deepening low and strong westerly winds aloft may support downslope flow over parts of the Rockies and High Plains with gusts of 20-30 mph. However, the late arrival of the trough, poorly timed with the diurnal cycle, will favor relatively poor overlap with low RH values. This should limit fire-weather concerns across the CONUS. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CST Sat Dec 14 2024 Valid 141700Z - 151200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 12/14/2024 .PREV DISCUSSION... /ISSUED 0200 AM CST Sat Dec 14 2024/ ...Synopsis... A progressive mid-level trough moving over the Southern Plains will rapidly move eastward as shortwave ridging develops over the Rockies and High Plains in its wake. A second mid-level trough farther west will begin to approach later this evening and overnight as increasingly strong westerly flow overspreads the Plains again. The ridging will initially favor weak surface winds and relatively mild temperatures through much of the day before the approaching trough aids in developing a lee cyclone over the central and northern High Plains. The deepening low and strong westerly winds aloft may support downslope flow over parts of the Rockies and High Plains with gusts of 20-30 mph. However, the late arrival of the trough, poorly timed with the diurnal cycle, will favor relatively poor overlap with low RH values. This should limit fire-weather concerns across the CONUS. ...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 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1030 AM CST Sat Dec 14 2024 Valid 141630Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...Coastal California... The Marginal Risk across parts of coastal CA has been removed with this update. The 12Z OAK sounding showed a dearth of boundary-layer instability, and a line of low-topped convection has weakened as it moves inland in tandem with a shortwave trough also tracking quickly eastward. While strong winds will remain possible in the short term given the enhanced low/mid-level flow noted on recent VWPs from KMUX, the lack of appreciable surface-based instability is expected to limit the overall severe threat for the rest of the period. ...East/Southeast Texas... A shortwave trough over the southern/central Plains this morning will continue to eject eastward across the mid MS Valley through tonight. Related surface low over eastern KS is forecast to weaken in this time frame, as high pressure will remain entrenched over the East Coast. A cold front is expected to stall over parts of east to central TX later today. While a favorably moist low-level airmass will be in place ahead of this front, limited large-scale ascent and poor lapse rates aloft should hinder robust updrafts and organized severe potential across east/southeast TX. ..Gleason/Halbert.. 12/14/2024 Read more

MD 2267 CONCERNING FREEZING RAIN FOR EASTERN IOWA...NORTHWESTERN ILLINOIS...AND VICINITY
Mesoscale Discussion 2267 NWS Storm Prediction Center Norman OK 0458 AM CST Sat Dec 14 2024 Areas affected...eastern Iowa...northwestern Illinois...and vicinity Concerning...Freezing rain Valid 141058Z - 141700Z SUMMARY...Freezing rain -- at rates locally in excess of 0.10"/hour -- will continue spreading north-northeastward across eastern Iowa and into northwestern Illinois through midday. DISCUSSION...Latest radar loop shows an expansive area of precipitation ongoing from the Arklatex region northward across the Lower Missouri and Mid Mississippi Valleys this morning. The precipitation is occurring in an area of warm advection/quasigeostropic ascent, east of a 1013 mb surface low over central Kansas, and associated upper low moving eastward across Nebraska and Kansas this morning. A cold boundary layer remains in place across this region, on the western fringe of a 1048 mb high centered in the vicinity of the Pennsylvania/New York border area. As low-level theta-e advection continues ascending atop the cold low-level airmass, resulting ascent will continue to support the broad/ongoing area of precipitation over the next several hours. Currently, the surface freezing line extends from the Omaha area east-southeastward into southern Illinois north of the St. Louis area. North of this line, mixed/wintry precipitation is observed, mainly in the form of freezing rain. The most substantial freezing rain has occurred over southeastern Iowa recently, with KOTM (Ottumwa) reporting 0.13" in the past hour. This area of moderate precipitation will continue spreading north-northeastward with time, across eastern Iowa and northwestern Illinois, with ice accumulations likely. ..Goss.. 12/14/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LOT...ILX...MKX...LSX...DVN...ARX...DMX...EAX... LAT...LON 40859281 42109289 43389206 43369069 42498949 41588893 40229008 40169187 40859281 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Sat Dec 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE BAY AREA AND NEARBY COASTAL CALIFORNIA... ...SUMMARY... Isolated strong to marginally severe, low-topped thunderstorms are possible for a few more hours across the Bay Area and nearby coastal California. ...Synopsis... A progressive mid/upper-level pattern over the CONUS features two primary troughs promoting convective potential this period, from east to west: 1. A strong shortwave trough was apparent in moisture-channel imagery over the central Plains from west-central NE to western OK, with a 500-mb low apparent near HYS. The low is expected to move eastward along I-70 into near COU by 00Z, with trough northward to southern IA and southward to southern AR. By the end of the period, the low should reach northeastern IL around IKK, along a trough aligned roughly from MKE-BNA. 2. A synoptic-scale trough from the Gulf of Alaska to offshore from the CA Coast, including a small cyclone off western WA and a basal shortwave now approaching coastal central/northern CA. At the surface, 11Z analysis showed a low over KS between ICT-FRI, with cold front southwestward across southwestern OK and portions of west-central/southwest TX. By 00Z, the low should become nearly stacked under the 500-mb low over north-central MO, with cold front extending over northwestern AR, and northeast TX, to near AUS and between DRT-LRD. Substantial weakening of the front should be underway by then, especially south of the Ozarks, with surface winds less than 10 kt on both sides of the front over east and south TX. The TX portion of the front should nearly dissipate overnight. ...Bay Area and vicinity... Isolated strong-severe gusts and hail near severe limits are possible this morning near the coast, in about a 150-nm-long corridor centered just south of SFO. A low-level frontal band precedes the basal shortwave trough over CA, with associated precip forecast to continue spreading obliquely eastward/southeastward down the Sierra and -- to a lesser extent -- over central/southern CA. Behind that, strong cooling aloft -- related to DCVA immediately preceding the mid/upper trough -- is supporting favorable instability through a deep-enough layer for thunderstorms, with areas of 200-500 J/kg MLCAPE apparent over the Pacific marine layer between SFO and the OR border. That plume of buoyancy will expand southeastward past the MRY area over the next few hours, combining with favorable deep shear (40-50 kt effective-shear magnitudes) to support slight onshore penetration of strong/isolated severe thunderstorms, before activity weakens in lower inland theta-e. Convection should move over the outlook area through midmorning local time, before the trough passes. ...East to southeast TX... Large-scale ascent preceding the eastern mid/upper trough -- in the form of DCVA over northern parts of the thunder outlook area and a broad plume of low-level WAA/moisture transport -- will continue to support scattered, predominantly elevated thunderstorm potential from the Arklatex to the lower Missouri and mid Mississippi Valleys. Farther south across east TX to near the upper TX Coast, isolated to widely scattered thunderstorms are possible through this afternoon. This activity also will be tied mainly to the WAA plume, and related isentropic ascent to LFC. Forecast soundings show potential for inflow-layer parcels to become surface-based amid continuing warming from both advective and diabatic processes. Wind profiles will veer with height, though lower midlevel (roughly 600-700 mb) weaknesses and lack of greater winds even higher in altitude will limit bulk shear, with effective-shear magnitudes generally remaining below 40 kt. Counterbalancing effects precluding unconditional severe threat include rising heights throughout the day, stable layers and other areas of weak lapse rates in midlevels that will keep MLCAPE from getting much greater than 1000 J/kg, and weakening of both frontal and large-scale lift with time. ..Edwards/Goss.. 12/14/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Sat Dec 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE BAY AREA AND NEARBY COASTAL CALIFORNIA... ...SUMMARY... Isolated strong to marginally severe, low-topped thunderstorms are possible for a few more hours across the Bay Area and nearby coastal California. ...Synopsis... A progressive mid/upper-level pattern over the CONUS features two primary troughs promoting convective potential this period, from east to west: 1. A strong shortwave trough was apparent in moisture-channel imagery over the central Plains from west-central NE to western OK, with a 500-mb low apparent near HYS. The low is expected to move eastward along I-70 into near COU by 00Z, with trough northward to southern IA and southward to southern AR. By the end of the period, the low should reach northeastern IL around IKK, along a trough aligned roughly from MKE-BNA. 2. A synoptic-scale trough from the Gulf of Alaska to offshore from the CA Coast, including a small cyclone off western WA and a basal shortwave now approaching coastal central/northern CA. At the surface, 11Z analysis showed a low over KS between ICT-FRI, with cold front southwestward across southwestern OK and portions of west-central/southwest TX. By 00Z, the low should become nearly stacked under the 500-mb low over north-central MO, with cold front extending over northwestern AR, and northeast TX, to near AUS and between DRT-LRD. Substantial weakening of the front should be underway by then, especially south of the Ozarks, with surface winds less than 10 kt on both sides of the front over east and south TX. The TX portion of the front should nearly dissipate overnight. ...Bay Area and vicinity... Isolated strong-severe gusts and hail near severe limits are possible this morning near the coast, in about a 150-nm-long corridor centered just south of SFO. A low-level frontal band precedes the basal shortwave trough over CA, with associated precip forecast to continue spreading obliquely eastward/southeastward down the Sierra and -- to a lesser extent -- over central/southern CA. Behind that, strong cooling aloft -- related to DCVA immediately preceding the mid/upper trough -- is supporting favorable instability through a deep-enough layer for thunderstorms, with areas of 200-500 J/kg MLCAPE apparent over the Pacific marine layer between SFO and the OR border. That plume of buoyancy will expand southeastward past the MRY area over the next few hours, combining with favorable deep shear (40-50 kt effective-shear magnitudes) to support slight onshore penetration of strong/isolated severe thunderstorms, before activity weakens in lower inland theta-e. Convection should move over the outlook area through midmorning local time, before the trough passes. ...East to southeast TX... Large-scale ascent preceding the eastern mid/upper trough -- in the form of DCVA over northern parts of the thunder outlook area and a broad plume of low-level WAA/moisture transport -- will continue to support scattered, predominantly elevated thunderstorm potential from the Arklatex to the lower Missouri and mid Mississippi Valleys. Farther south across east TX to near the upper TX Coast, isolated to widely scattered thunderstorms are possible through this afternoon. This activity also will be tied mainly to the WAA plume, and related isentropic ascent to LFC. Forecast soundings show potential for inflow-layer parcels to become surface-based amid continuing warming from both advective and diabatic processes. Wind profiles will veer with height, though lower midlevel (roughly 600-700 mb) weaknesses and lack of greater winds even higher in altitude will limit bulk shear, with effective-shear magnitudes generally remaining below 40 kt. Counterbalancing effects precluding unconditional severe threat include rising heights throughout the day, stable layers and other areas of weak lapse rates in midlevels that will keep MLCAPE from getting much greater than 1000 J/kg, and weakening of both frontal and large-scale lift with time. ..Edwards/Goss.. 12/14/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Sat Dec 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE BAY AREA AND NEARBY COASTAL CALIFORNIA... ...SUMMARY... Isolated strong to marginally severe, low-topped thunderstorms are possible for a few more hours across the Bay Area and nearby coastal California. ...Synopsis... A progressive mid/upper-level pattern over the CONUS features two primary troughs promoting convective potential this period, from east to west: 1. A strong shortwave trough was apparent in moisture-channel imagery over the central Plains from west-central NE to western OK, with a 500-mb low apparent near HYS. The low is expected to move eastward along I-70 into near COU by 00Z, with trough northward to southern IA and southward to southern AR. By the end of the period, the low should reach northeastern IL around IKK, along a trough aligned roughly from MKE-BNA. 2. A synoptic-scale trough from the Gulf of Alaska to offshore from the CA Coast, including a small cyclone off western WA and a basal shortwave now approaching coastal central/northern CA. At the surface, 11Z analysis showed a low over KS between ICT-FRI, with cold front southwestward across southwestern OK and portions of west-central/southwest TX. By 00Z, the low should become nearly stacked under the 500-mb low over north-central MO, with cold front extending over northwestern AR, and northeast TX, to near AUS and between DRT-LRD. Substantial weakening of the front should be underway by then, especially south of the Ozarks, with surface winds less than 10 kt on both sides of the front over east and south TX. The TX portion of the front should nearly dissipate overnight. ...Bay Area and vicinity... Isolated strong-severe gusts and hail near severe limits are possible this morning near the coast, in about a 150-nm-long corridor centered just south of SFO. A low-level frontal band precedes the basal shortwave trough over CA, with associated precip forecast to continue spreading obliquely eastward/southeastward down the Sierra and -- to a lesser extent -- over central/southern CA. Behind that, strong cooling aloft -- related to DCVA immediately preceding the mid/upper trough -- is supporting favorable instability through a deep-enough layer for thunderstorms, with areas of 200-500 J/kg MLCAPE apparent over the Pacific marine layer between SFO and the OR border. That plume of buoyancy will expand southeastward past the MRY area over the next few hours, combining with favorable deep shear (40-50 kt effective-shear magnitudes) to support slight onshore penetration of strong/isolated severe thunderstorms, before activity weakens in lower inland theta-e. Convection should move over the outlook area through midmorning local time, before the trough passes. ...East to southeast TX... Large-scale ascent preceding the eastern mid/upper trough -- in the form of DCVA over northern parts of the thunder outlook area and a broad plume of low-level WAA/moisture transport -- will continue to support scattered, predominantly elevated thunderstorm potential from the Arklatex to the lower Missouri and mid Mississippi Valleys. Farther south across east TX to near the upper TX Coast, isolated to widely scattered thunderstorms are possible through this afternoon. This activity also will be tied mainly to the WAA plume, and related isentropic ascent to LFC. Forecast soundings show potential for inflow-layer parcels to become surface-based amid continuing warming from both advective and diabatic processes. Wind profiles will veer with height, though lower midlevel (roughly 600-700 mb) weaknesses and lack of greater winds even higher in altitude will limit bulk shear, with effective-shear magnitudes generally remaining below 40 kt. Counterbalancing effects precluding unconditional severe threat include rising heights throughout the day, stable layers and other areas of weak lapse rates in midlevels that will keep MLCAPE from getting much greater than 1000 J/kg, and weakening of both frontal and large-scale lift with time. ..Edwards/Goss.. 12/14/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Sat Dec 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE BAY AREA AND NEARBY COASTAL CALIFORNIA... ...SUMMARY... Isolated strong to marginally severe, low-topped thunderstorms are possible for a few more hours across the Bay Area and nearby coastal California. ...Synopsis... A progressive mid/upper-level pattern over the CONUS features two primary troughs promoting convective potential this period, from east to west: 1. A strong shortwave trough was apparent in moisture-channel imagery over the central Plains from west-central NE to western OK, with a 500-mb low apparent near HYS. The low is expected to move eastward along I-70 into near COU by 00Z, with trough northward to southern IA and southward to southern AR. By the end of the period, the low should reach northeastern IL around IKK, along a trough aligned roughly from MKE-BNA. 2. A synoptic-scale trough from the Gulf of Alaska to offshore from the CA Coast, including a small cyclone off western WA and a basal shortwave now approaching coastal central/northern CA. At the surface, 11Z analysis showed a low over KS between ICT-FRI, with cold front southwestward across southwestern OK and portions of west-central/southwest TX. By 00Z, the low should become nearly stacked under the 500-mb low over north-central MO, with cold front extending over northwestern AR, and northeast TX, to near AUS and between DRT-LRD. Substantial weakening of the front should be underway by then, especially south of the Ozarks, with surface winds less than 10 kt on both sides of the front over east and south TX. The TX portion of the front should nearly dissipate overnight. ...Bay Area and vicinity... Isolated strong-severe gusts and hail near severe limits are possible this morning near the coast, in about a 150-nm-long corridor centered just south of SFO. A low-level frontal band precedes the basal shortwave trough over CA, with associated precip forecast to continue spreading obliquely eastward/southeastward down the Sierra and -- to a lesser extent -- over central/southern CA. Behind that, strong cooling aloft -- related to DCVA immediately preceding the mid/upper trough -- is supporting favorable instability through a deep-enough layer for thunderstorms, with areas of 200-500 J/kg MLCAPE apparent over the Pacific marine layer between SFO and the OR border. That plume of buoyancy will expand southeastward past the MRY area over the next few hours, combining with favorable deep shear (40-50 kt effective-shear magnitudes) to support slight onshore penetration of strong/isolated severe thunderstorms, before activity weakens in lower inland theta-e. Convection should move over the outlook area through midmorning local time, before the trough passes. ...East to southeast TX... Large-scale ascent preceding the eastern mid/upper trough -- in the form of DCVA over northern parts of the thunder outlook area and a broad plume of low-level WAA/moisture transport -- will continue to support scattered, predominantly elevated thunderstorm potential from the Arklatex to the lower Missouri and mid Mississippi Valleys. Farther south across east TX to near the upper TX Coast, isolated to widely scattered thunderstorms are possible through this afternoon. This activity also will be tied mainly to the WAA plume, and related isentropic ascent to LFC. Forecast soundings show potential for inflow-layer parcels to become surface-based amid continuing warming from both advective and diabatic processes. Wind profiles will veer with height, though lower midlevel (roughly 600-700 mb) weaknesses and lack of greater winds even higher in altitude will limit bulk shear, with effective-shear magnitudes generally remaining below 40 kt. Counterbalancing effects precluding unconditional severe threat include rising heights throughout the day, stable layers and other areas of weak lapse rates in midlevels that will keep MLCAPE from getting much greater than 1000 J/kg, and weakening of both frontal and large-scale lift with time. ..Edwards/Goss.. 12/14/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Sat Dec 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE BAY AREA AND NEARBY COASTAL CALIFORNIA... ...SUMMARY... Isolated strong to marginally severe, low-topped thunderstorms are possible for a few more hours across the Bay Area and nearby coastal California. ...Synopsis... A progressive mid/upper-level pattern over the CONUS features two primary troughs promoting convective potential this period, from east to west: 1. A strong shortwave trough was apparent in moisture-channel imagery over the central Plains from west-central NE to western OK, with a 500-mb low apparent near HYS. The low is expected to move eastward along I-70 into near COU by 00Z, with trough northward to southern IA and southward to southern AR. By the end of the period, the low should reach northeastern IL around IKK, along a trough aligned roughly from MKE-BNA. 2. A synoptic-scale trough from the Gulf of Alaska to offshore from the CA Coast, including a small cyclone off western WA and a basal shortwave now approaching coastal central/northern CA. At the surface, 11Z analysis showed a low over KS between ICT-FRI, with cold front southwestward across southwestern OK and portions of west-central/southwest TX. By 00Z, the low should become nearly stacked under the 500-mb low over north-central MO, with cold front extending over northwestern AR, and northeast TX, to near AUS and between DRT-LRD. Substantial weakening of the front should be underway by then, especially south of the Ozarks, with surface winds less than 10 kt on both sides of the front over east and south TX. The TX portion of the front should nearly dissipate overnight. ...Bay Area and vicinity... Isolated strong-severe gusts and hail near severe limits are possible this morning near the coast, in about a 150-nm-long corridor centered just south of SFO. A low-level frontal band precedes the basal shortwave trough over CA, with associated precip forecast to continue spreading obliquely eastward/southeastward down the Sierra and -- to a lesser extent -- over central/southern CA. Behind that, strong cooling aloft -- related to DCVA immediately preceding the mid/upper trough -- is supporting favorable instability through a deep-enough layer for thunderstorms, with areas of 200-500 J/kg MLCAPE apparent over the Pacific marine layer between SFO and the OR border. That plume of buoyancy will expand southeastward past the MRY area over the next few hours, combining with favorable deep shear (40-50 kt effective-shear magnitudes) to support slight onshore penetration of strong/isolated severe thunderstorms, before activity weakens in lower inland theta-e. Convection should move over the outlook area through midmorning local time, before the trough passes. ...East to southeast TX... Large-scale ascent preceding the eastern mid/upper trough -- in the form of DCVA over northern parts of the thunder outlook area and a broad plume of low-level WAA/moisture transport -- will continue to support scattered, predominantly elevated thunderstorm potential from the Arklatex to the lower Missouri and mid Mississippi Valleys. Farther south across east TX to near the upper TX Coast, isolated to widely scattered thunderstorms are possible through this afternoon. This activity also will be tied mainly to the WAA plume, and related isentropic ascent to LFC. Forecast soundings show potential for inflow-layer parcels to become surface-based amid continuing warming from both advective and diabatic processes. Wind profiles will veer with height, though lower midlevel (roughly 600-700 mb) weaknesses and lack of greater winds even higher in altitude will limit bulk shear, with effective-shear magnitudes generally remaining below 40 kt. Counterbalancing effects precluding unconditional severe threat include rising heights throughout the day, stable layers and other areas of weak lapse rates in midlevels that will keep MLCAPE from getting much greater than 1000 J/kg, and weakening of both frontal and large-scale lift with time. ..Edwards/Goss.. 12/14/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0227 AM CST Sat Dec 14 2024 Valid 171200Z - 221200Z ...DISCUSSION... An upper trough over the High Plains vicinity Day 4/Tue morning will deepen and track east to the MS Valley by Day 5/Wed, and to the Atlantic coast by Day 6/Thu. As this occurs, a cold front will move across the south-central and southeast states, pushing offshore the Gulf and Atlantic coasts by late Day 5/Wed into early Day 6/Thu. While thunderstorm potential will be possible with this system, severe potential appears limited, given weak instability and deep-layer flow oriented parallel to the surface boundary (leading to more anafrontal processes). With the strong front moving well into the Gulf of Mexico, boundary-layer moisture will remain scant heading into the end of the forecast period, and severe-thunderstorm potential is expected to remain low Days 7-8/Fri-Sat. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0227 AM CST Sat Dec 14 2024 Valid 171200Z - 221200Z ...DISCUSSION... An upper trough over the High Plains vicinity Day 4/Tue morning will deepen and track east to the MS Valley by Day 5/Wed, and to the Atlantic coast by Day 6/Thu. As this occurs, a cold front will move across the south-central and southeast states, pushing offshore the Gulf and Atlantic coasts by late Day 5/Wed into early Day 6/Thu. While thunderstorm potential will be possible with this system, severe potential appears limited, given weak instability and deep-layer flow oriented parallel to the surface boundary (leading to more anafrontal processes). With the strong front moving well into the Gulf of Mexico, boundary-layer moisture will remain scant heading into the end of the forecast period, and severe-thunderstorm potential is expected to remain low Days 7-8/Fri-Sat. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0227 AM CST Sat Dec 14 2024 Valid 171200Z - 221200Z ...DISCUSSION... An upper trough over the High Plains vicinity Day 4/Tue morning will deepen and track east to the MS Valley by Day 5/Wed, and to the Atlantic coast by Day 6/Thu. As this occurs, a cold front will move across the south-central and southeast states, pushing offshore the Gulf and Atlantic coasts by late Day 5/Wed into early Day 6/Thu. While thunderstorm potential will be possible with this system, severe potential appears limited, given weak instability and deep-layer flow oriented parallel to the surface boundary (leading to more anafrontal processes). With the strong front moving well into the Gulf of Mexico, boundary-layer moisture will remain scant heading into the end of the forecast period, and severe-thunderstorm potential is expected to remain low Days 7-8/Fri-Sat. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0227 AM CST Sat Dec 14 2024 Valid 171200Z - 221200Z ...DISCUSSION... An upper trough over the High Plains vicinity Day 4/Tue morning will deepen and track east to the MS Valley by Day 5/Wed, and to the Atlantic coast by Day 6/Thu. As this occurs, a cold front will move across the south-central and southeast states, pushing offshore the Gulf and Atlantic coasts by late Day 5/Wed into early Day 6/Thu. While thunderstorm potential will be possible with this system, severe potential appears limited, given weak instability and deep-layer flow oriented parallel to the surface boundary (leading to more anafrontal processes). With the strong front moving well into the Gulf of Mexico, boundary-layer moisture will remain scant heading into the end of the forecast period, and severe-thunderstorm potential is expected to remain low Days 7-8/Fri-Sat. Read more

MD 2266 CONCERNING FREEZING RAIN FOR PARTS OF NORTH CENTRAL MISSOURI INTO SOUTHEASTERN IOWA
Mesoscale Discussion 2266 NWS Storm Prediction Center Norman OK 1141 PM CST Fri Dec 13 2024 Areas affected...parts of north central Missouri into southeastern Iowa Concerning...Freezing rain Valid 140541Z - 140945Z SUMMARY...Rain and embedded thunderstorms forming across western Missouri during the next few hours appear likely to continue developing northeastward and eastward overnight, supporting moderate freezing rain with potential for appreciable icing north-northwest of Kirksville MO through the Ottumwa IA vicinity by 2-4 AM CST. DISCUSSION...Downstream of a notable short wave trough progressing across the central Great Plains, moisture return within a developing area of large-scale ascent, rooted within lower/mid-tropospheric warm advection, is contributing to an ongoing gradual increase in precipitation northeast of the middle/lower Missouri Valley into eastern Oklahoma. From east of the Sioux Falls area into southeastern Iowa, this appears focused along a 700 mb baroclinic zone which is forecast to slowly develop northward toward the upper Mississippi Valley overnight. Southward across western Missouri into eastern Oklahoma, this appears generally aligned with better lower-level moisture return along one branch of a strong low-level jet (40-50 kt around 850 mb), which is forecast to slowly shift eastward toward the middle Mississippi Valley through 08-10Z. Models indicate that substantive further warming and moistening along the low-level jet will contribute to sufficient steepening of mid-level lapse rates to support weak CAPE above a slowly modifying, but still cold and stable near surface environment across much of Missouri into Iowa. Based on the latest NAM/Rapid Refresh, among other output, it appears that this may be accompanied by a blossoming band of convection and perhaps embedded weak thunderstorm activity north of Springfield MO through and north of Kirksville by 07-08Z, before continuing to spread northeastward and eastward. North/northwest of Kirksville, northeastward across the Ottumwa vicinity of southeastern Iowa, forecast soundings indicate that a pronounced warm nose will continue to develop above sub-freezing boundary-layer air, which may be maintained (aided initially by evaporative cooling of precipitation) as far south as portions of north central Missouri at least into the 10-11Z time frame. This may allow for appreciable ice accrual as developing convection supports a sustained period of moderate freezing rain, including rates occasionally on the order of 1/4+ inch per hour. ..Kerr.. 12/14/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LSX...DVN...DMX...EAX... LAT...LON 40239343 41359317 41749235 41399167 40719191 40289234 40069292 40239343 Read more