SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Wed Dec 18 2024 Valid 181300Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE TENNESSEE VALLEY REGION... ...SUMMARY... Isolated damaging wind gusts and a brief tornado are possible into early afternoon across parts of the Tennessee Valley region. ...Synopsis... A continuing progressive pattern aloft will be dominated by two main shortwave troughs: a trailing perturbation now over the coastal Pacific Northwest, and a positively tilted one apparent in moisture- channel imagery near a DBQ-STJ-P28-DHT axis. The latter will be the main mid/upper-level convective influence this period, as it elongates and tracks to near a PIT-LEX-ELD-GLS line by 00Z. The southern part of the trough is progged to amplify and become less positively tilted as it crosses the Mississippi Delta region tonight, reaching northern GA, eastern AL and the western FL Panhandle by 12Z. At the surface, 11Z analysis showed a cold front across parts of northern/western KY, western TN, southern AR, and northeast/central/ southwest TX. By 00Z, the front should extend from a low over northern NJ southwestward, roughly along the Blue Ridge, then over northern GA to the FL Panhandle. By the end of the period, the cold front should be off all the Atlantic Coast except central FL, extending southwestward to the southern Gulf. ...TN and vicinity... Isolated, damaging to marginally severe gusts and/or a brief tornado are possible into the afternoon, mainly over portions of TN. A near-frontal band of thunderstorms was ongoing from the Arklatex region across the Mid-South, to central KY. Ahead of this activity, a northward-narrowing corridor of 60s F surface dewpoints (and related near-surface-based effective-inflow parcels) was evident, supporting 250-750 J/kg MLCAPE from near MEM to northwest of BNA, where the 12Z sounding still showed a stable boundary layer. See SPC Mesoscale Discussion 2272 for near-term info. Weak, continuing, preconvective theta-e advection, and perhaps a few deg F of cloud-restrained diurnal warming, will offset modest midlevel lapse rates enough to maintain and perhaps slightly increase surface-based buoyancy eastward across TN through early/mid afternoon. Although flow ahead of the QLCS that has not already done so should veer to south-southwest or southwest, enough hodograph enlargement will remain to support around 100-150 J/kg 0-500m SRH and 200-300 J/kg effective SRH, amid 35-45-kt effective-shear magnitudes. As such, the main concern will arise from episodic, embedded BOW/LEWP formations and accompanying mesocirculations. The convective band should outpace the already marginally unstable boundary layer by midafternoon. ..Edwards/Goss.. 12/18/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0651 AM CST Wed Dec 18 2024 Valid 181300Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE TENNESSEE VALLEY REGION... ...SUMMARY... Isolated damaging wind gusts and a brief tornado are possible into early afternoon across parts of the Tennessee Valley region. ...Synopsis... A continuing progressive pattern aloft will be dominated by two main shortwave troughs: a trailing perturbation now over the coastal Pacific Northwest, and a positively tilted one apparent in moisture- channel imagery near a DBQ-STJ-P28-DHT axis. The latter will be the main mid/upper-level convective influence this period, as it elongates and tracks to near a PIT-LEX-ELD-GLS line by 00Z. The southern part of the trough is progged to amplify and become less positively tilted as it crosses the Mississippi Delta region tonight, reaching northern GA, eastern AL and the western FL Panhandle by 12Z. At the surface, 11Z analysis showed a cold front across parts of northern/western KY, western TN, southern AR, and northeast/central/ southwest TX. By 00Z, the front should extend from a low over northern NJ southwestward, roughly along the Blue Ridge, then over northern GA to the FL Panhandle. By the end of the period, the cold front should be off all the Atlantic Coast except central FL, extending southwestward to the southern Gulf. ...TN and vicinity... Isolated, damaging to marginally severe gusts and/or a brief tornado are possible into the afternoon, mainly over portions of TN. A near-frontal band of thunderstorms was ongoing from the Arklatex region across the Mid-South, to central KY. Ahead of this activity, a northward-narrowing corridor of 60s F surface dewpoints (and related near-surface-based effective-inflow parcels) was evident, supporting 250-750 J/kg MLCAPE from near MEM to northwest of BNA, where the 12Z sounding still showed a stable boundary layer. See SPC Mesoscale Discussion 2272 for near-term info. Weak, continuing, preconvective theta-e advection, and perhaps a few deg F of cloud-restrained diurnal warming, will offset modest midlevel lapse rates enough to maintain and perhaps slightly increase surface-based buoyancy eastward across TN through early/mid afternoon. Although flow ahead of the QLCS that has not already done so should veer to south-southwest or southwest, enough hodograph enlargement will remain to support around 100-150 J/kg 0-500m SRH and 200-300 J/kg effective SRH, amid 35-45-kt effective-shear magnitudes. As such, the main concern will arise from episodic, embedded BOW/LEWP formations and accompanying mesocirculations. The convective band should outpace the already marginally unstable boundary layer by midafternoon. ..Edwards/Goss.. 12/18/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0339 AM CST Wed Dec 18 2024 Valid 211200Z - 261200Z ...DISCUSSION... Strong surface high pressure and a dearth of boundary-layer moisture will preclude severe thunderstorm potential on Days 4-5/Sat-Sun. By Day 6/Mon, medium range forecast guidance shows a series of upper shortwave troughs shifting east from the Rockies to the MS Valley through Day 8/Wed (Christmas Day). In response, lee troughing/surface low developing is expected over parts of the southern Plains. Increasing southerly low-level flow will support modest northward transport of Gulf moisture across parts of TX into OK, and eventually the Lower MS Valley near the end of the period. While there is still quite a bit of spread with regards to intensity, location, and timing of these features, increasing thunderstorm activity is expected Day 6-8/Mon-Wed across the southern Plains vicinity. While uncertainty is high, if timing and overlap of key features comes to fruition, some severe risk could be possible over the upcoming Christmas holiday period. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0339 AM CST Wed Dec 18 2024 Valid 211200Z - 261200Z ...DISCUSSION... Strong surface high pressure and a dearth of boundary-layer moisture will preclude severe thunderstorm potential on Days 4-5/Sat-Sun. By Day 6/Mon, medium range forecast guidance shows a series of upper shortwave troughs shifting east from the Rockies to the MS Valley through Day 8/Wed (Christmas Day). In response, lee troughing/surface low developing is expected over parts of the southern Plains. Increasing southerly low-level flow will support modest northward transport of Gulf moisture across parts of TX into OK, and eventually the Lower MS Valley near the end of the period. While there is still quite a bit of spread with regards to intensity, location, and timing of these features, increasing thunderstorm activity is expected Day 6-8/Mon-Wed across the southern Plains vicinity. While uncertainty is high, if timing and overlap of key features comes to fruition, some severe risk could be possible over the upcoming Christmas holiday period. Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0203 AM CST Wed Dec 18 2024 Valid 201200Z - 211200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are not expected across the Lower 48 on Friday. ...Synopsis... A broad upper trough will envelop much of the eastern half of the CONUS on Friday. Meanwhile, another upper trough will approach the Pacific coast late in the period, while upper ridging persists over the West. At the surface, high pressure will build over the central U.S. and a cold front will develop well south into the Gulf of Mexico and offshore the Atlantic coast. This will result in a dry continental airmass over much of the U.S. Isolated thunderstorms are possible over warmer waters offshore from the FL east coast and the Outer Banks. Any thunderstorms associated with the eastern Pacific upper trough will remain well offshore as well. Given a dearth of boundary-layer moisture and a stable airmass, inland thunderstorms are not expected across the Lower 48 on Friday. ..Leitman.. 12/18/2024 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0203 AM CST Wed Dec 18 2024 Valid 201200Z - 211200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are not expected across the Lower 48 on Friday. ...Synopsis... A broad upper trough will envelop much of the eastern half of the CONUS on Friday. Meanwhile, another upper trough will approach the Pacific coast late in the period, while upper ridging persists over the West. At the surface, high pressure will build over the central U.S. and a cold front will develop well south into the Gulf of Mexico and offshore the Atlantic coast. This will result in a dry continental airmass over much of the U.S. Isolated thunderstorms are possible over warmer waters offshore from the FL east coast and the Outer Banks. Any thunderstorms associated with the eastern Pacific upper trough will remain well offshore as well. Given a dearth of boundary-layer moisture and a stable airmass, inland thunderstorms are not expected across the Lower 48 on Friday. ..Leitman.. 12/18/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0158 AM CST Wed Dec 18 2024 Valid 191200Z - 201200Z ...NO CRITICAL AREAS... ...Synopsis... Mid-level ridging over the western US is forecast to move eastward Thursday as the overall upper-air pattern becomes more amplified. At the surface, high pressure over the Great Basin will move into the Rockies. Aside from some residual offshore flow over parts of southern CA, widespread fire-weather concerns are not expected. ...Southern CA... Offshore winds are expected to gradually diminish overnight D1/Wednesday and into early D2/Thursday, as high pressure over the Great Basin shifts eastward. While winds should generally weaken, some lingering, locally elevated fire-weather conditions may continue in the typical Santa Ana mountains/foothills through the afternoon. Limited in spatial coverage and duration, fire-weather concerns are not expected to be widespread. ..Lyons.. 12/18/2024 ...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 0158 AM CST Wed Dec 18 2024 Valid 191200Z - 201200Z ...NO CRITICAL AREAS... ...Synopsis... Mid-level ridging over the western US is forecast to move eastward Thursday as the overall upper-air pattern becomes more amplified. At the surface, high pressure over the Great Basin will move into the Rockies. Aside from some residual offshore flow over parts of southern CA, widespread fire-weather concerns are not expected. ...Southern CA... Offshore winds are expected to gradually diminish overnight D1/Wednesday and into early D2/Thursday, as high pressure over the Great Basin shifts eastward. While winds should generally weaken, some lingering, locally elevated fire-weather conditions may continue in the typical Santa Ana mountains/foothills through the afternoon. Limited in spatial coverage and duration, fire-weather concerns are not expected to be widespread. ..Lyons.. 12/18/2024 ...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 0157 AM CST Wed Dec 18 2024 Valid 181200Z - 191200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF LOS ANGELES AND VENTURA COUNTIES IN SOUTHERN CALIFORNIA... ...Synopsis... Mid-level ridging over the western US is forecast to intensify through the forecast period, as the overall flow pattern amplifies. Surface high pressure over the Great Basin will continue to build, supporting offshore flow across parts of southern CA. Santa Ana winds, in combination with low RH values, should allow for several hours of elevated to critical fire-weather conditions across southern CA. ...Southern CA... High pressure in the Great Basin will drive offshore winds across parts of southern California early this morning, continuing through the afternoon. With the offshore pressure gradient remaining fairly strong (-4 to -6 mb) through the first half of the day, gusts of 40-50 mph through the terrain-favored corridors and on ridge tops are expected. Several hours of critical fire weather conditions are likely across portions of Los Angeles and Ventura Counties, with RH values below 15%. Winds are expected to slowly diminish during the evening and overnight as the pressure gradient weakens into early D2/Thur. ..Lyons.. 12/18/2024 ...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 0157 AM CST Wed Dec 18 2024 Valid 181200Z - 191200Z ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF LOS ANGELES AND VENTURA COUNTIES IN SOUTHERN CALIFORNIA... ...Synopsis... Mid-level ridging over the western US is forecast to intensify through the forecast period, as the overall flow pattern amplifies. Surface high pressure over the Great Basin will continue to build, supporting offshore flow across parts of southern CA. Santa Ana winds, in combination with low RH values, should allow for several hours of elevated to critical fire-weather conditions across southern CA. ...Southern CA... High pressure in the Great Basin will drive offshore winds across parts of southern California early this morning, continuing through the afternoon. With the offshore pressure gradient remaining fairly strong (-4 to -6 mb) through the first half of the day, gusts of 40-50 mph through the terrain-favored corridors and on ridge tops are expected. Several hours of critical fire weather conditions are likely across portions of Los Angeles and Ventura Counties, with RH values below 15%. Winds are expected to slowly diminish during the evening and overnight as the pressure gradient weakens into early D2/Thur. ..Lyons.. 12/18/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1149 PM CST Tue Dec 17 2024 Valid 191200Z - 201200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not expected on Thursday. ...Florida... A shortwave upper trough within the area of broader eastern CONUS troughing will be oriented from the Carolinas to the northeast Gulf of Mexico Thursday morning. This system will shift east across FL and offshore the Atlantic coast through 00z. At the surface, a cold front located over north FL early in the day will develop southward across the Peninsula. Low-level flow will be veered/northerly ahead of the front, resulting in little low-level convergence. Additionally, stronger large-scale ascent will remain well north of the Peninsula. While weak destabilization is forecast (500-1000 J/kg MLCAPE), mainly over the southern Peninsula, poor lapse rates and warm midlevel temperatures will preclude severe thunderstorm potential. Most CAMs and calibrated thunder guidance also indicate little thunderstorm activity. Will maintain 10 percent general thunder probabilities for the southeast FL coast, but even that may be generous. ..Leitman.. 12/18/2024 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1147 PM CST Tue Dec 17 2024 Valid 181200Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE TENNESSEE VALLEY... ...SUMMARY... Isolated damaging wind gusts and a brief tornado are possible through mid-day across parts of the Tennessee Valley. ...Tennessee Valley... A mid-level trough will move into the mid Mississippi Valley today, as an associated cold front advances southeastward through the Ohio and Tennessee Valleys. At the start of the period, a line of thunderstorms is expected to be located from central Kentucky southwestward across western Tennessee into eastern Arkansas. This line will move eastward toward the southern Appalachians this morning. Although instability is forecast to weaken ahead of the line during the morning, the southern edge of the low-level jet is expected to be over Tennessee where surface dewpoints will be in the mid to upper 50s F. This should be enough to maintain a marginal severe threat this morning. RAP forecast soundings in middle Tennessee at 15Z have curved hodograhps, with storm-relative helicity near 300 ms/s2 and 0-6 km shear around 40 knots. This environment should support isolated severe storms along the more organized parts of the line. The stronger cells embedded in the line could produce isolated severe gusts and potentially a brief tornado. This line, along with the severe threat, is expected to weaken by midday as the stronger low-level flow moves northeastward away from the region. ..Broyles/Lyons.. 12/18/2024 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0654 PM CST Tue Dec 17 2024 Valid 180100Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE ARK-LA-TEX AND MID MISSISSIPPI VALLEY... ...SUMMARY... Marginally severe thunderstorms associated with isolated severe gusts and hail will be possible from late this evening into early Wednesday morning from parts of the Ark-La-Tex into the mid Mississippi Valley. ...Ark-La-Tex/Mid Mississippi Valley... A mid-level trough will move southeastward across the central U.S. tonight, as an associated cold front advances southeastward into the Ark-La-Tex and mid Mississippi Valley. Ahead of the front, moisture advection will gradually increase surface dewpoints into the lower to mid 60s F from northeast Texas to western Tennessee. In response, destabilization will take place ahead of the front with MUCAPE increasing into the 1000 to 1500 J/kg range. As low-level convergence strengthens near the front late this evening, scattered thunderstorm initiation is expected. As cell coverage increases, a line of storms will likely develop just ahead of the front around midnight. This line is forecast to move southeastward across the Ark-La-Tex and mid Mississippi Valley during the overnight period. RAP forecast soundings after midnight near the expected location of the line in northeastern Arkansas have a temperature inversion in the boundary layer, with instability primarily located above 700 mb. This elevated instability combined with effective shear of 30 to 40 knots may be enough for a marginal severe threat overnight as the low-level jet gradually strengthens. Severe gusts and hail will be the primary threats, especially if cells can become surface-based within the stronger low-level flow. As the line moves southeastward across eastern Arkansas and western Tennessee late tonight into early Wednesday morning, a brief tornado will also be possible. However, low to mid-level lapse rates are forecast to be poor, which will help to limit the severe weather risk. ..Broyles.. 12/18/2024 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0654 PM CST Tue Dec 17 2024 Valid 180100Z - 181200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE ARK-LA-TEX AND MID MISSISSIPPI VALLEY... ...SUMMARY... Marginally severe thunderstorms associated with isolated severe gusts and hail will be possible from late this evening into early Wednesday morning from parts of the Ark-La-Tex into the mid Mississippi Valley. ...Ark-La-Tex/Mid Mississippi Valley... A mid-level trough will move southeastward across the central U.S. tonight, as an associated cold front advances southeastward into the Ark-La-Tex and mid Mississippi Valley. Ahead of the front, moisture advection will gradually increase surface dewpoints into the lower to mid 60s F from northeast Texas to western Tennessee. In response, destabilization will take place ahead of the front with MUCAPE increasing into the 1000 to 1500 J/kg range. As low-level convergence strengthens near the front late this evening, scattered thunderstorm initiation is expected. As cell coverage increases, a line of storms will likely develop just ahead of the front around midnight. This line is forecast to move southeastward across the Ark-La-Tex and mid Mississippi Valley during the overnight period. RAP forecast soundings after midnight near the expected location of the line in northeastern Arkansas have a temperature inversion in the boundary layer, with instability primarily located above 700 mb. This elevated instability combined with effective shear of 30 to 40 knots may be enough for a marginal severe threat overnight as the low-level jet gradually strengthens. Severe gusts and hail will be the primary threats, especially if cells can become surface-based within the stronger low-level flow. As the line moves southeastward across eastern Arkansas and western Tennessee late tonight into early Wednesday morning, a brief tornado will also be possible. However, low to mid-level lapse rates are forecast to be poor, which will help to limit the severe weather risk. ..Broyles.. 12/18/2024 Read more

No watches are valid as of Tue Dec 17 22:35:01 UTC 2024.

No Mesoscale Discussions are in effect as of Tue Dec 17 22:35:01 UTC 2024.