SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0636 PM CST Sat Dec 14 2024 Valid 150100Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not expected through tonight. ...Discussion... Overall thunderstorm coverage will remain very isolated tonight. Convection near the cold core of a shortwave trough over central MO has nocturnally weakened. Still, scant elevated buoyancy might yield sporadic flashes as the trough continues east towards southern IN, and within the broad but modest low-level warm conveyor arcing back into the Ark-La-Miss. Greater buoyancy will remain confined to east TX but weak large-scale ascent suggests thunderstorm probabilities will be low. Sporadic thunderstorms may linger longest across parts of the Pacific Northwest coast. Here, steep mid-level lapse rates around 8 C/km per 00Z UIL/SLE soundings will eventually weaken as mid-level temperatures warm from south to north in the early morning. ..Grams.. 12/15/2024 Read more

No Mesoscale Discussions are in effect as of Sat Dec 14 22:22:02 UTC 2024.

No watches are valid as of Sat Dec 14 22:22:02 UTC 2024.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0320 PM CST Sat Dec 14 2024 Valid 161200Z - 221200Z A quasi-zonal, progressive upper-level pattern will be present this weekend into the middle of next week. Thereafter, some flow amplification is forecast to occur. Upper-level troughing will be the general pattern in the East with ridging over portions of the West. This pattern will favor cold air east of the Divide with seasonably warm temperatures farther west. Some colder air/high pressure will filter into the Great Basin and drive offshore winds in parts of southern California. With the passage of successive upper-level shortwave troughs, some dry and breezy conditions are possible in parts of the High Plains. Where precipitation remains minimal, locally heightened fire concerns could develop next week. Given the cooler temperatures expected, critical fire weather probability will remain low. Offshore flow in southern California will likely be the main area of concern for fire weather. The offshore pressure gradient still appears it will be maximized Tuesday night into Wednesday morning. Deterministic and ensemble guidance has not changed significantly in terms of the upper-level and surface pattern over the past several model cycles. Upper-level wind support should be minimal. The main variation in guidance is with the magnitude of the offshore pressure gradient. 40% critical probabilities will remain for Tuesday/Wednesday and trends in the offshore gradient will continue to be monitored. ..Wendt.. 12/14/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0153 PM CST Sat Dec 14 2024 Valid 142000Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...20Z Update... The western edge of thunderstorm probabilities have been trimmed in the middle MS Valley vicinity, where additional thunderstorm development appears unlikely behind the strongly forced band of convection shifting eastward -- in tandem with the midlevel shortwave trough. Farther west, thunderstorm probabilities were also removed over portions of the Coastal Range in northern CA. Forecast soundings suggest EL temperatures/instability are no longer supportive of lightning here. For additional details, see the previous discussion below. ..Weinman.. 12/14/2024 .PREV DISCUSSION... /ISSUED 1030 AM CST Sat Dec 14 2024/ ...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. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0153 PM CST Sat Dec 14 2024 Valid 142000Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Organized severe thunderstorms are not expected through tonight. ...20Z Update... The western edge of thunderstorm probabilities have been trimmed in the middle MS Valley vicinity, where additional thunderstorm development appears unlikely behind the strongly forced band of convection shifting eastward -- in tandem with the midlevel shortwave trough. Farther west, thunderstorm probabilities were also removed over portions of the Coastal Range in northern CA. Forecast soundings suggest EL temperatures/instability are no longer supportive of lightning here. For additional details, see the previous discussion below. ..Weinman.. 12/14/2024 .PREV DISCUSSION... /ISSUED 1030 AM CST Sat Dec 14 2024/ ...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. Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0142 PM CST Sat Dec 14 2024 Valid 151200Z - 161200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 12/14/2024 .PREV DISCUSSION... /ISSUED 0202 AM CST Sat Dec 14 2024/ ...Synopsis... As the mid-level trough ejects over the central Rockies and into the Plains early D2/Sunday, a lee low and trailing surface trough will quickly deepen across parts of the High Plains. At the same time, a cold front will approach from the interior West. Aided by strong mid-level westerlies at the base of the trough and downslope pressure gradients, several hours of strong surface winds (20-30 mph) are likely across parts of the central High Plains. These strong winds may briefly overlap with areas of moderately low RH (~30%) across western NE and eastern WY. Farther south into eastern NM and far West TX, lower RH will remain possible with more mild temperatures and diurnal minimums of 20-25%. However, winds here are expected to be slower and more transient, owing to the weaker surface pressure falls and flow aloft. The net result will be a few hours of locally dry and breezy conditions in the lee of the Rockies where fuels are somewhat dry. While there is some risk, fire-weather concerns are not expected to be widespread, given the brief nature of the strong winds and lower RH, as well as the passage of the cold front Sunday evening. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0142 PM CST Sat Dec 14 2024 Valid 151200Z - 161200Z ...NO CRITICAL AREAS... No changes to the ongoing forecast. ..Wendt.. 12/14/2024 .PREV DISCUSSION... /ISSUED 0202 AM CST Sat Dec 14 2024/ ...Synopsis... As the mid-level trough ejects over the central Rockies and into the Plains early D2/Sunday, a lee low and trailing surface trough will quickly deepen across parts of the High Plains. At the same time, a cold front will approach from the interior West. Aided by strong mid-level westerlies at the base of the trough and downslope pressure gradients, several hours of strong surface winds (20-30 mph) are likely across parts of the central High Plains. These strong winds may briefly overlap with areas of moderately low RH (~30%) across western NE and eastern WY. Farther south into eastern NM and far West TX, lower RH will remain possible with more mild temperatures and diurnal minimums of 20-25%. However, winds here are expected to be slower and more transient, owing to the weaker surface pressure falls and flow aloft. The net result will be a few hours of locally dry and breezy conditions in the lee of the Rockies where fuels are somewhat dry. While there is some risk, fire-weather concerns are not expected to be widespread, given the brief nature of the strong winds and lower RH, as well as the passage of the cold front Sunday evening. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0116 PM CST Sat Dec 14 2024 Valid 161200Z - 171200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential is expected to be low on Monday. ...Synopsis... A mid-level trough will amplify and become negatively tilted on Monday as it moves from the central Plains to the Northeast by 12Z Tuesday. A surface low will move from northern Minnesota to northern Ontario on Monday with a cold front extending from this surface low to the Great Lakes and the southern Plains. This front will likely become stationary from central Texas to northern Mississippi late in the period. Continued southerly flow ahead of the surface low will bring low 60s dewpoints as far north as the Missouri Bootheel Monday afternoon with mid 60s dewpoints farther south near the ArkLaTex. An expansive precipitation shield is likely across the eastern Great Lakes on Monday afternoon and evening in response to a strengthening low-level jet along and ahead of the surface front, however limited moisture will keep instability subdued and lightning appears unlikely with this activity. Modest instability may develop with the richer moisture from southern Illinois to the southern Plains. However, forcing will be weaker across this region and shear will be weak farther south (ArkLaTex) where the greater instability will be present. The lack of phase between the instability, shear, and forcing make severe thunderstorms unlikely on Monday. ..Bentley.. 12/14/2024 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0116 PM CST Sat Dec 14 2024 Valid 161200Z - 171200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential is expected to be low on Monday. ...Synopsis... A mid-level trough will amplify and become negatively tilted on Monday as it moves from the central Plains to the Northeast by 12Z Tuesday. A surface low will move from northern Minnesota to northern Ontario on Monday with a cold front extending from this surface low to the Great Lakes and the southern Plains. This front will likely become stationary from central Texas to northern Mississippi late in the period. Continued southerly flow ahead of the surface low will bring low 60s dewpoints as far north as the Missouri Bootheel Monday afternoon with mid 60s dewpoints farther south near the ArkLaTex. An expansive precipitation shield is likely across the eastern Great Lakes on Monday afternoon and evening in response to a strengthening low-level jet along and ahead of the surface front, however limited moisture will keep instability subdued and lightning appears unlikely with this activity. Modest instability may develop with the richer moisture from southern Illinois to the southern Plains. However, forcing will be weaker across this region and shear will be weak farther south (ArkLaTex) where the greater instability will be present. The lack of phase between the instability, shear, and forcing make severe thunderstorms unlikely on Monday. ..Bentley.. 12/14/2024 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1117 AM CST Sat Dec 14 2024 Valid 151200Z - 161200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential is expected to remain limited on Sunday. ...Synopsis... An upper trough will shift east into the Plains Sunday night into early Monday. As a result, enhanced deep-layer southwesterly mid/upper flow will envelop the central/southern Plains toward the Mid/Upper MS Valley. At the surface, a deepening low will track east along the international border in the vicinity of the northern Plains and Upper Midwest. A trailing cold front is forecast to move southeast across much of the northern/central Plains and Upper Midwest, becoming positioned from central MO southwestward into northwest TX by 12z Monday. Southerly low-level flow ahead of the aforementioned front will allow upper 50s to mid 60s dewpoints to spread northward across much of TX into eastern OK, LA, AR and southern MO. Shortwave upper ridging for much of the period prior to 03z will likely preclude thunderstorm activity within the warm conveyor. However, stronger height falls associated with the ejecting trough will overspread the southern Plains (though stronger large-scale ascent will remain focused further north). As a result, isolated to scattered, mostly elevated, thunderstorms are anticipated after 06Z from eastern Oklahoma into north-central Arkansas and southern Missouri, along and ahead of the southeastward advancing cold front. Instability is expected to be mostly weak, particularly farther north where greater forcing will be present. Therefore, despite favorable shear across the warm sector, storm mode is expected to be messy given the lack of stronger buoyancy, weak lapse rates, and the tendency for storms to be undercut by the surface front through time. The expectation of limited storm organization amid weak instability precludes the need for a marginal risk at this time. ..Bentley.. 12/14/2024 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 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

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

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