SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1251 AM CDT Wed Sep 11 2024 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE FL PANHANDLE TO CENTRAL AL AND IN EASTERN MT... ...SUMMARY... On Thursday, a few tornadoes will be possible, mainly in the morning and afternoon from the Florida Panhandle to north-central Alabama. Scattered large hail and severe gusts will also be possible across the eastern Montana vicinity during the afternoon to early evening. ...FL Panhandle to the TN Valley... Hurricane Francine is forecast by NHC to be in a weakening phase from a tropical storm to a depression on Thursday, as it steadily moves north from parts of western/central MS into the Mid-South. With this process occurring throughout D2, tornado potential should be focused during the first half of the period. Rather enlarged low-level hodographs initially should gradually shrink from south to north, but will remain overlapped with rich 70s surface dew points through at least the afternoon. Consensus of CAM guidance largely suggests multiple opportunities for convective bands during this time frame. Primary threat in the morning should initially be confined across the FL Panhandle into south AL. This should shift north along the leading edge of the rich tropical moisture into central to perhaps north AL during the afternoon. The northern extent of the low-probability tornado threat over the TN Valley appears nebulous, where scant surface-based buoyancy can become coincident with large SRH. ...Eastern MT vicinity... A northern Rockies to Great Basin shortwave trough will move gradually east into the northern High Plains to central Rockies by Thursday evening. Guidance remains highly consistent with the ejection of an embedded impulse and attendant meridional mid-level jetlet impinging on the eastern MT/WY region during the late afternoon to early evening. This will increase large-scale ascent and deep-layer shear, while being favorably timed with peak boundary-layer heating. Spread in guidance is greater with the degree of available buoyancy as boundary-layer moisture remains limited. But a ribbon of low to mid 50s surface dew points appears plausible on the backside of a deep surface cyclone drifting from far eastern MT into south SK. This would support a confined corridor of at least weak buoyancy, which should be enhanced by cooling mid-level temperatures with the approaching trough. Scattered thunderstorms should develop near the WY/MT border area during the mid to late afternoon and quickly advance north-northeast. Amid a highly elongated mid to upper hodograph, long-lived mid-level rotation and small-scale bowing segments may occur, capable of producing swaths of large hail and severe gusts through about dusk. ..Grams.. 09/11/2024 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1247 AM CDT Wed Sep 11 2024 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL GULF COAST... ...SUMMARY... A few tornadoes are possible across the central Gulf Coast vicinity on Wednesday into Wednesday night, in association with Tropical Cyclone Francine. ...Central Gulf Coast... Hurricane Francine is forecast to continue northeastward across the northwest Gulf of Mexico today, likely making landfall over the central LA Coast during the afternoon. Easterly/northeasterly winds are expected across much of the Southeast from the morning through the afternoon, which will likely keep the tropical airmass associated with this cyclone offshore (or only over immediate coastal portions of south-central and southeast LA). As the storm makes landfall, mid 70s dewpoints will spread northward into more of southeast LA, southern MS, southern AL, and the far western FL Panhandle during the evening. This increased low-level moisture could boast buoyancy enough for more sustained/persistent updrafts. Robust low to mid-level wind fields associated with the cyclone will support rotation within any more persistent updrafts, with some isolated low-topped supercells possible. Current guidance suggests the highest tornado potential will exist from 21Z through 04Z from far southeast LA across southern MS/AL. Mid 70s dewpoints and southerly/southeasterly surface winds will persist from southern MS/AL into the far western FL Panhandle, supporting a low-probability tornado risk through early Thursday morning. ...Parts of the Northwest/Northern Rockies... The strong shortwave trough currently off the Pacific Northwest coast is forecast to continue eastward throughout the period, while also deepening/maturing. By early Thursday morning, this shortwave trough will likely extend from the ID Chimney/northwest MT into the Great Basin. Strong mid-level flow will accompany this shortwave, spreading eastward from northern CA through the Great Basin as the wave progresses eastward. Relatively cool mid-level temperatures are already in place from the northern Intermountain West into the northern Rockies, with 500 mb temperatures from -11.5 to -14 deg C sampled on the regional 00Z soundings. Strong heating and boundary-layer mixing beneath these cool mid-level temperature will result in modest buoyancy during the afternoon ahead of the shortwave trough. Afternoon thunderstorm development is anticipated as large-scale ascent increases amid this destabilized and modest buoyant airmass. The stronger flow and vertical shear will be displaced south of the region, but moderate shear combined with the cool temperatures aloft could still contribute to some isolated hail. High cloud bases and resultant strong outflow could result in some gusty winds as well. ...Northern High Plains... Lee surface troughing will deepen throughout the day, with southeasterly surface winds increasing in response. Strong heating/mixing is anticipated across the region. Low-level moisture advection may help offset some of this mixing but dewpoints will likely still drop into the mid 40s to low 50s across much of the region. Highest dewpoints are anticipated across northeastern MT and western North Dakota. Even with this limited moisture, the strong heating should destabilize the airmass. Late afternoon thunderstorms are anticipated with this destabilized airmass as both increasing large-scale ascent and low-level convergence provide the lift needed for convective initiation. Vertical shear will likely be strong enough for some updraft organization (particularly across northwest MT), and high cloud bases will contribute to the potential for strong outflow capable of damaging gusts. ..Mosier/Lyons.. 09/11/2024 Read more

SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0738 PM CDT Tue Sep 10 2024 Valid 110100Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL AND SOUTHEAST LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...01Z Update... An increasing, but low-probability, tornado threat is still anticipated tonight into early Wednesday morning over the LA Coast as rainbands associated with TC Francine move across the area. Isolated thunderstorms will continue across the central/southern Rockies and central High Plains for the next several hours before waning buoyancy and nocturnal stabilization result in diminishing coverage. Additional thunderstorms are also still expected tonight through tomorrow morning along the Pacific Northwest coast and into the northern Rockies as a strong shortwave trough approaches the Pacific Northwest coast. ..Mosier.. 09/11/2024 Read more

No watches are valid as of Tue Sep 10 22:24:01 UTC 2024.

No Mesoscale Discussions are in effect as of Tue Sep 10 22:24:01 UTC 2024.

SPC Day 3-8 Fire Weather Outlook
Day 3-8 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0327 PM CDT Tue Sep 10 2024 Valid 121200Z - 181200Z An upper-level trough will be lifting northeastward through the northern Rockies and into the northern Plains on Thursday. A deep lee cyclone/trough will develop in response. By the weekend, upper-level ridging will build back into the central U.S. with another upper-level trough expected to move into the West Coast late Sunday into Monday. With the precipitation expected with the initial trough this week, in combination with forecast precipitation with the trough next week, fire weather concerns this weekend into next week are fairly uncertain. ...Central/Northern Plains... Strong surface winds are anticipated on Thursday as a deep surface trough develops in the northern High Plains region. Winds of 15-25 mph (with areas of higher gusts) are possible given strong winds should extend into the lowest 2-3 km. RH will likely be lowest along the central/northern High Plains area where downslope drying will be maximized. Farther east, RH is still expected to fall to near and around 20-25%. Fine fuels will especially be supportive of fire spread. Sustained critical conditions are expected where the strongest mid-level winds and low-level jet will roughly overlap. There is some uncertainty introduced by potential convection in the surface trough, but dry/windy conditions should last long enough before that convection develops. Critical conditions could occur farther south and possibly farther east, but duration is not certain and fuels are less receptive to the east. ...Eastern Great Basin... Surface winds will likely be strong on Thursday in eastern Utah into western Colorado. Given areas of recent rainfall and the overall downward trends in ERC percentiles, the degree of fire weather concern is rather uncertain. Despite dry and windy conditions, highlights will be withheld pending updated fuel information suggesting a greater concern. ...Parts of Upper-Midwest/Ohio Valley... As Francine is forecast by NHC to move into the mid-Mississippi Valley on Thursday, there is potential for surface winds to increase in parts of Illinois/Indiana/Ohio. Forecast soundings do show some potential for at least some upper-level clouds. Depending on the degree of surface heating and the surface pressure gradient, some locally elevated fire weather appears possible given the dry fuels in place. ..Wendt.. 09/10/2024 ...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 0240 PM CDT Tue Sep 10 2024 Valid 102000Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL/SOUTHEAST LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...20z Update... The forecast remains on track and no changes are needed to the D1 Convective Outlook. See previous discussion below for more information. ..Thornton/Gleason.. 09/10/2024 .PREV DISCUSSION... /ISSUED 1122 AM CDT Tue Sep 10 2024/ ...Southern Louisiana Late Tonight/Early Wednesday Morning... The latest NHC forecast indicates Tropical Cyclone Francine will move northeastward over the western Gulf of Mexico tonight through early Wednesday morning. Morning surface observations show a stalled front remains situated over the northern Gulf, with greater low-level moisture (mid/upper 70s surface dewpoints) generally confined near or just off the LA/MS/AL Gulf Coast. As Francine approaches the LA Coast late tonight, this very moist low-level airmass over the northern Gulf should gradually spread inland along parts of the immediate central Gulf Coast, supporting weak boundary-layer instability. As Francine approaches, a corresponding increase in low-level flow and related effective SRH should support some threat for tornadoes with any low-topped supercells in outer rain bands to the east-northeast of the central circulation. Latest guidance continues to suggest that the better tornado potential over land will occur in the Day 2/Wednesday time frame (after 12Z). But, an isolated/marginal tornado threat still remains apparent along parts of the LA Coast for the last few hours of the Day 1 period (08-12Z) early Wednesday morning, where a Marginal Risk has been maintained. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0240 PM CDT Tue Sep 10 2024 Valid 102000Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL/SOUTHEAST LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...20z Update... The forecast remains on track and no changes are needed to the D1 Convective Outlook. See previous discussion below for more information. ..Thornton/Gleason.. 09/10/2024 .PREV DISCUSSION... /ISSUED 1122 AM CDT Tue Sep 10 2024/ ...Southern Louisiana Late Tonight/Early Wednesday Morning... The latest NHC forecast indicates Tropical Cyclone Francine will move northeastward over the western Gulf of Mexico tonight through early Wednesday morning. Morning surface observations show a stalled front remains situated over the northern Gulf, with greater low-level moisture (mid/upper 70s surface dewpoints) generally confined near or just off the LA/MS/AL Gulf Coast. As Francine approaches the LA Coast late tonight, this very moist low-level airmass over the northern Gulf should gradually spread inland along parts of the immediate central Gulf Coast, supporting weak boundary-layer instability. As Francine approaches, a corresponding increase in low-level flow and related effective SRH should support some threat for tornadoes with any low-topped supercells in outer rain bands to the east-northeast of the central circulation. Latest guidance continues to suggest that the better tornado potential over land will occur in the Day 2/Wednesday time frame (after 12Z). But, an isolated/marginal tornado threat still remains apparent along parts of the LA Coast for the last few hours of the Day 1 period (08-12Z) early Wednesday morning, where a Marginal Risk has been maintained. Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 PM CDT Tue Sep 10 2024 Valid 121200Z - 131200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE SOUTHEAST...AND FROM EASTERN MONTANA INTO THE FAR WESTERN DAKOTAS... ...SUMMARY... A low-probability tornado threat may persist into Thursday across parts of the Deep South. Isolated large hail and severe gusts will be possible over the northern High Plains vicinity on Thursday afternoon and evening. ...Synopsis... An upper trough over the Great Basin will eject northeastward into the northern Rockies/High Plains through Friday morning, with moderate midlevel meridional flow aloft. Accompanying this trough will be a cold front which will extend from eastern MT into eastern WY. To the east, TC Francine is forecast to move northward up the lower MS valley, with strong southerly winds helping to bring moisture north across much of the Southeast east of the center/low. High pressure will remain over the Mid Atlantic, adding to the pressure gradient east of the cyclone. ...Eastern MT into the western Dakotas... Daytime heating as well as cooling aloft with the upper trough will result in steepening lapse rates, though low-level moisture will be meager with 40s dewpoints primarily east of the cold front. A narrow band of uncapped and unstable air will still develop during the late afternoon, with around 1000 J/kg MUCAPE and 40 kt deep-layer effective shear. As such, scattered cells are likely to develop along the front, and the elongated hodographs may favor a few single cells despite linear forcing mechanism. Therefore isolated hail over 1.00" may occur, as well as brief bowing segments producing strong gusts. ...Much of AL, eastern MS...FL Panhandle... Scattered thunderstorms are likely to exist from the northeastern quadrant of TC Francine arcing southeastward across much of AL and into the FL Panhandle Thursday morning. Low-level theta-e advection will exist near a warm front as it lifts north across AL, though dry air will exist from the Appalachians into parts of the OH/TN Valleys initially. The greatest risk of a couple tornadoes will likely be limited to storms within the instability plume centered over AL, and including the FL Panhandle and perhaps far eastern MS. Low-level shear will be strong to start the day, but will be reduced as the system continues north and low-level flow veers. ..Jewell.. 09/10/2024 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0213 PM CDT Tue Sep 10 2024 Valid 121200Z - 131200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE SOUTHEAST...AND FROM EASTERN MONTANA INTO THE FAR WESTERN DAKOTAS... ...SUMMARY... A low-probability tornado threat may persist into Thursday across parts of the Deep South. Isolated large hail and severe gusts will be possible over the northern High Plains vicinity on Thursday afternoon and evening. ...Synopsis... An upper trough over the Great Basin will eject northeastward into the northern Rockies/High Plains through Friday morning, with moderate midlevel meridional flow aloft. Accompanying this trough will be a cold front which will extend from eastern MT into eastern WY. To the east, TC Francine is forecast to move northward up the lower MS valley, with strong southerly winds helping to bring moisture north across much of the Southeast east of the center/low. High pressure will remain over the Mid Atlantic, adding to the pressure gradient east of the cyclone. ...Eastern MT into the western Dakotas... Daytime heating as well as cooling aloft with the upper trough will result in steepening lapse rates, though low-level moisture will be meager with 40s dewpoints primarily east of the cold front. A narrow band of uncapped and unstable air will still develop during the late afternoon, with around 1000 J/kg MUCAPE and 40 kt deep-layer effective shear. As such, scattered cells are likely to develop along the front, and the elongated hodographs may favor a few single cells despite linear forcing mechanism. Therefore isolated hail over 1.00" may occur, as well as brief bowing segments producing strong gusts. ...Much of AL, eastern MS...FL Panhandle... Scattered thunderstorms are likely to exist from the northeastern quadrant of TC Francine arcing southeastward across much of AL and into the FL Panhandle Thursday morning. Low-level theta-e advection will exist near a warm front as it lifts north across AL, though dry air will exist from the Appalachians into parts of the OH/TN Valleys initially. The greatest risk of a couple tornadoes will likely be limited to storms within the instability plume centered over AL, and including the FL Panhandle and perhaps far eastern MS. Low-level shear will be strong to start the day, but will be reduced as the system continues north and low-level flow veers. ..Jewell.. 09/10/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0204 PM CDT Tue Sep 10 2024 Valid 111200Z - 121200Z ...CRITICAL FIRE WEATHER AREA FOR A LARGE PORTION OF THE GREAT BASIN... Minor modifications to the critical area have been made on account of recent guidance. The remainder of the forecast remains on track. See the previous discussion for greater details. ..Wendt.. 09/10/2024 .PREV DISCUSSION... /ISSUED 0202 AM CDT Tue Sep 10 2024/ ...Synopsis... The upper trough over the western US will quickly intensify Wednesday, as a shortwave perturbation and mid-level jet streak move onshore over the West Coast. As the trough strengthens, mid-level flow over much of the West will increase. A surface low will deepen over the northern Great Basin, while a cold front moves onshore and also strengthens. To the east, TS Francine will approach the Gulf Coast with offshore winds likely over parts of the mid South. Strong surface winds, low humidity, and thunderstorms over parts of the West and central US will support critical fire-weather concerns Wednesday. ...Great Basin... Ahead of the deepening trough, a potent mid-level jet streak will move over parts of the western Great Basin beginning early Wednesday. A deepening surface low in parts of the eastern Basin will drive 20-25 mph winds over much of NV into western UT. Augmented by downslope flow off the Sierra and the approaching cold front, a brief period of winds of 25-30 mph will be possible along with RH below 15%. Widespread critical fire-weather conditions are likely over parts of the Great Basin. Fire-weather concerns should diminish behind the front as cooler and more quiescent conditions are expected behind the front into early Thursday. ...Lee of the Rockies and High Plains... As the trough approaches, height falls and stronger flow aloft will overspread the Rockies and High Plains. A surface low will deepen first in eastern MT, with a lee trough extending south into the central High Plains. Near the lee trough, strong southerly winds will overlap with areas of low RH and drying fine fuels. Elevated fire weather concerns are expected over parts of the High Plains Wednesday afternoon and evening. ...Mid South... As Francine approaches the Gulf Coast Wednesday and Wednesday night, offshore pressure gradients will increase over parts of the lower MS Valley and Mid South. While humidity values are not expected to be overly low with the tropical air mass approaching, strong gusts are expected to overlap with areas of relatively dry fuels and little recent rainfall. Brief elevated fire-weather conditions are possible before rain chances increase into early Thursday. ...Northwest Thunder... Ahead of the cold front, increasing mid-level moisture and strong lift from the trough will promote scattered thunderstorms Wednesday afternoon. Lightning may interact with areas of somewhat drier fuels over parts of the Northwest and northern Rockies before broader wetting rainfall develops. However, these storms will likely have higher precipitation efficiency with a cooler air mass and more plentiful Pacific moisture in place. This lends significant uncertainty on the threat for any lightning ignitions. ...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 0204 PM CDT Tue Sep 10 2024 Valid 111200Z - 121200Z ...CRITICAL FIRE WEATHER AREA FOR A LARGE PORTION OF THE GREAT BASIN... Minor modifications to the critical area have been made on account of recent guidance. The remainder of the forecast remains on track. See the previous discussion for greater details. ..Wendt.. 09/10/2024 .PREV DISCUSSION... /ISSUED 0202 AM CDT Tue Sep 10 2024/ ...Synopsis... The upper trough over the western US will quickly intensify Wednesday, as a shortwave perturbation and mid-level jet streak move onshore over the West Coast. As the trough strengthens, mid-level flow over much of the West will increase. A surface low will deepen over the northern Great Basin, while a cold front moves onshore and also strengthens. To the east, TS Francine will approach the Gulf Coast with offshore winds likely over parts of the mid South. Strong surface winds, low humidity, and thunderstorms over parts of the West and central US will support critical fire-weather concerns Wednesday. ...Great Basin... Ahead of the deepening trough, a potent mid-level jet streak will move over parts of the western Great Basin beginning early Wednesday. A deepening surface low in parts of the eastern Basin will drive 20-25 mph winds over much of NV into western UT. Augmented by downslope flow off the Sierra and the approaching cold front, a brief period of winds of 25-30 mph will be possible along with RH below 15%. Widespread critical fire-weather conditions are likely over parts of the Great Basin. Fire-weather concerns should diminish behind the front as cooler and more quiescent conditions are expected behind the front into early Thursday. ...Lee of the Rockies and High Plains... As the trough approaches, height falls and stronger flow aloft will overspread the Rockies and High Plains. A surface low will deepen first in eastern MT, with a lee trough extending south into the central High Plains. Near the lee trough, strong southerly winds will overlap with areas of low RH and drying fine fuels. Elevated fire weather concerns are expected over parts of the High Plains Wednesday afternoon and evening. ...Mid South... As Francine approaches the Gulf Coast Wednesday and Wednesday night, offshore pressure gradients will increase over parts of the lower MS Valley and Mid South. While humidity values are not expected to be overly low with the tropical air mass approaching, strong gusts are expected to overlap with areas of relatively dry fuels and little recent rainfall. Brief elevated fire-weather conditions are possible before rain chances increase into early Thursday. ...Northwest Thunder... Ahead of the cold front, increasing mid-level moisture and strong lift from the trough will promote scattered thunderstorms Wednesday afternoon. Lightning may interact with areas of somewhat drier fuels over parts of the Northwest and northern Rockies before broader wetting rainfall develops. However, these storms will likely have higher precipitation efficiency with a cooler air mass and more plentiful Pacific moisture in place. This lends significant uncertainty on the threat for any lightning ignitions. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1219 PM CDT Tue Sep 10 2024 Valid 111200Z - 121200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN PARTS OF THE CENTRAL GULF COAST STATES... ...SUMMARY... A few tornadoes are possible across the central Gulf Coast vicinity on Wednesday into Wednesday night, in association with Tropical Cyclone Francine. ...Northern Gulf Coast... Francine is forecast to become a hurricane over the northwest Gulf of Mexico, with strengthening wind fields overspreading much of the central Gulf Coast states from Wednesday afternoon into the night. Preceding this system, a stationary front will exist roughly parallel to the coast, with the more unstable/tropical moisture to the south. As southerly winds increase east of the cyclone center, this will lift the front north as a warm front, with mid 70s F dewpoints spreading north across southern MS, AL, and the western FL Panhandle. Rapidly enlarging hodographs in the vicinity of the warm front may support a zone of tornado potential as bands of cells push northward off the Gulf of Mexico and arc northwestward. Tornado potential on the north side will be limited by the more stable air due to high pressure to the north. ...Parts of the Northwest/Northern Rockies... A strong shortwave trough will move across the Pacific Northwest and into the Great Basin, with substantial cooling aloft. A cold front will generally stretch from a low over western MT across central ID and into northern NV during the afternoon, with the strongest heating ahead of the front across NV, UT and western WY. Post frontal rain and a few thunderstorms are likely near the developing cold front early in the day from northern ID into eastern OR, with diurnal convection developing over southeast OR, southwest ID and northern NV. Deep-layer shear will not be particularly strong given that the primary speed max will dive southeastward across the Sierra. However, cool temperatures aloft may yield small hail, with scattered strong gusts with the larger clusters of storms. Additional marginally severe storms may occur from western MT into northwest WY near the deepening surface trough and aided by very steep lapse rates supporting strong gusts. ..Jewell.. 09/10/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Tue Sep 10 2024 Valid 101630Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL/SOUTHEAST LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...Southern Louisiana Late Tonight/Early Wednesday Morning... The latest NHC forecast indicates Tropical Cyclone Francine will move northeastward over the western Gulf of Mexico tonight through early Wednesday morning. Morning surface observations show a stalled front remains situated over the northern Gulf, with greater low-level moisture (mid/upper 70s surface dewpoints) generally confined near or just off the LA/MS/AL Gulf Coast. As Francine approaches the LA Coast late tonight, this very moist low-level airmass over the northern Gulf should gradually spread inland along parts of the immediate central Gulf Coast, supporting weak boundary-layer instability. As Francine approaches, a corresponding increase in low-level flow and related effective SRH should support some threat for tornadoes with any low-topped supercells in outer rain bands to the east-northeast of the central circulation. Latest guidance continues to suggest that the better tornado potential over land will occur in the Day 2/Wednesday time frame (after 12Z). But, an isolated/marginal tornado threat still remains apparent along parts of the LA Coast for the last few hours of the Day 1 period (08-12Z) early Wednesday morning, where a Marginal Risk has been maintained. ..Gleason/Bentley.. 09/10/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122 AM CDT Tue Sep 10 2024 Valid 101630Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF COASTAL/SOUTHEAST LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...Southern Louisiana Late Tonight/Early Wednesday Morning... The latest NHC forecast indicates Tropical Cyclone Francine will move northeastward over the western Gulf of Mexico tonight through early Wednesday morning. Morning surface observations show a stalled front remains situated over the northern Gulf, with greater low-level moisture (mid/upper 70s surface dewpoints) generally confined near or just off the LA/MS/AL Gulf Coast. As Francine approaches the LA Coast late tonight, this very moist low-level airmass over the northern Gulf should gradually spread inland along parts of the immediate central Gulf Coast, supporting weak boundary-layer instability. As Francine approaches, a corresponding increase in low-level flow and related effective SRH should support some threat for tornadoes with any low-topped supercells in outer rain bands to the east-northeast of the central circulation. Latest guidance continues to suggest that the better tornado potential over land will occur in the Day 2/Wednesday time frame (after 12Z). But, an isolated/marginal tornado threat still remains apparent along parts of the LA Coast for the last few hours of the Day 1 period (08-12Z) early Wednesday morning, where a Marginal Risk has been maintained. ..Gleason/Bentley.. 09/10/2024 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1108 AM CDT Tue Sep 10 2024 Valid 101700Z - 111200Z No changes to the ongoing forecast. ..Wendt.. 09/10/2024 .PREV DISCUSSION... /ISSUED 0159 AM CDT Tue Sep 10 2024/ ...Synopsis... Broad troughing over the Northwest will gradually intensify later today and tonight, as a stronger shortwave and mid-level jet approach from the eastern Pacific. Increasing flow aloft will move inland, supporting the potential for strong surface winds and low humidity over parts of the Northwest and Great Basin. Elevated to near-critical fire-weather conditions are likely. ...Great Basin... As the upper trough shifts east, mid-level flow should strengthen over parts of the western Great Basin. Gusty downslope winds are likely in the lee of the Sierra and across parts of southern NV and western UT. Surface winds of 15-25 mph should overlap with RH below 15%, and within areas of dry fuels this afternoon. Elevated to near-critical fire-weather conditions are likely across much of NV and into portions of northern CA, southern ID and far western UT. Confidence in the development of nearly to briefly critical meteorological conditions is highest over parts of southern NV where winds are expected to be slightly stronger. However, fuels here are also slightly less receptive, and the overlap of favorable wind/RH may also be briefer. Thus, confidence remains too low for critical highlights currently. ...Cascades and Columbia Gorge... Increasing mid-level winds will combine with a strong onshore pressure gradient behind the departing cold front to drive 15-20 mph winds through Cascade Gaps and into the western Columbia Basin. While cooler and more moderate, pockets of RH below 25% should overlap with the stronger winds. The duration of these breezy and somewhat dry conditions may be somewhat limited, but elevated to briefly critical fire weather conditions are possible within dry fuels. ...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 1108 AM CDT Tue Sep 10 2024 Valid 101700Z - 111200Z No changes to the ongoing forecast. ..Wendt.. 09/10/2024 .PREV DISCUSSION... /ISSUED 0159 AM CDT Tue Sep 10 2024/ ...Synopsis... Broad troughing over the Northwest will gradually intensify later today and tonight, as a stronger shortwave and mid-level jet approach from the eastern Pacific. Increasing flow aloft will move inland, supporting the potential for strong surface winds and low humidity over parts of the Northwest and Great Basin. Elevated to near-critical fire-weather conditions are likely. ...Great Basin... As the upper trough shifts east, mid-level flow should strengthen over parts of the western Great Basin. Gusty downslope winds are likely in the lee of the Sierra and across parts of southern NV and western UT. Surface winds of 15-25 mph should overlap with RH below 15%, and within areas of dry fuels this afternoon. Elevated to near-critical fire-weather conditions are likely across much of NV and into portions of northern CA, southern ID and far western UT. Confidence in the development of nearly to briefly critical meteorological conditions is highest over parts of southern NV where winds are expected to be slightly stronger. However, fuels here are also slightly less receptive, and the overlap of favorable wind/RH may also be briefer. Thus, confidence remains too low for critical highlights currently. ...Cascades and Columbia Gorge... Increasing mid-level winds will combine with a strong onshore pressure gradient behind the departing cold front to drive 15-20 mph winds through Cascade Gaps and into the western Columbia Basin. While cooler and more moderate, pockets of RH below 25% should overlap with the stronger winds. The duration of these breezy and somewhat dry conditions may be somewhat limited, but elevated to briefly critical fire weather conditions are possible within dry fuels. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0743 AM CDT Tue Sep 10 2024 Valid 101300Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER COASTAL AREAS OF LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...Synopsis... In mid/upper levels, a strong shortwave trough now over the eastern Gulf of Alaska is forecast to dig southeastward and develop a closed 500-mb cyclone tonight, with the low about 150 nm west of AST by 12Z tomorrow. Ahead of this progressive and intensifying perturbation, height falls and strengthening cyclonic flow will spread across the northwestern CONUS throughout the period, combining with modest low/ middle-level moisture to support thunderstorm potential in parts of the Northwest, in addition to the diurnal-cycle convection across the Four Corners region, central/northern Rockies and parts of MT. Downstream, mid/upper flow should be nearly zonal from the Rockies across the Great Lakes. An embedded shortwave trough was evident in moisture-channel imagery over the Dakotas. This feature is forecast to move eastward to MN by 00Z, then across the Upper Great Lakes to Lake Huron and adjoining parts of ON by 12Z. Farther south, a weak, cut-off, mid/upper-level low over north-central TX should drift erratically near its present location, while increasingly influencing the path of Tropical Storm Francine. The 11Z surface analysis showed a wavy, quasistationary frontal zone fro Atlantic waters offshore SC, across northern FL to near the Mississippi River mouth, then a warm front arching across Gulf waters just south of the LA and TX Coasts, and into western parts of the Francine circulation. This boundary should move little from about 90W eastward, but remain a warm front over the upper TX and LA coastal waters, diffusely shifting inland over southern LA through the period. ...LA Coast... T.S. Francine -- initially centered southeast of BRO -- is forecast by NHC to turn northeastward across the northwestern Gulf today and become a hurricane, then move ashore in Louisiana on day 2. Suitably rich low-level moisture already is in place over coastal LA, and scattered to numerous showers and thunderstorms should cover the outlook area throughout much of the period, even well northeast of Francine's center. However, supercell potential will await sufficiently strong wind fields reaching the coastline ahead of the cyclone to enlarge hodographs favorably -- likely during the last few hours of the period. Then, tornado potential will be a matter of having relatively distinct/discrete, outer-band convection that can survive long enough to mature into supercells before weakening again in more-stable inflow air -- either inland or in broader precip areas. Unconditional probabilities are kept at marginal levels for now, given the late timing of the favorable kinematic fields, the nocturnal min in overland instability, and convective/ structural uncertainties with Francine. ..Edwards/Kerr.. 09/10/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0743 AM CDT Tue Sep 10 2024 Valid 101300Z - 111200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER COASTAL AREAS OF LOUISIANA... ...SUMMARY... Marginal tornado potential may reach coastal areas of Louisiana during the late overnight/early morning hours. ...Synopsis... In mid/upper levels, a strong shortwave trough now over the eastern Gulf of Alaska is forecast to dig southeastward and develop a closed 500-mb cyclone tonight, with the low about 150 nm west of AST by 12Z tomorrow. Ahead of this progressive and intensifying perturbation, height falls and strengthening cyclonic flow will spread across the northwestern CONUS throughout the period, combining with modest low/ middle-level moisture to support thunderstorm potential in parts of the Northwest, in addition to the diurnal-cycle convection across the Four Corners region, central/northern Rockies and parts of MT. Downstream, mid/upper flow should be nearly zonal from the Rockies across the Great Lakes. An embedded shortwave trough was evident in moisture-channel imagery over the Dakotas. This feature is forecast to move eastward to MN by 00Z, then across the Upper Great Lakes to Lake Huron and adjoining parts of ON by 12Z. Farther south, a weak, cut-off, mid/upper-level low over north-central TX should drift erratically near its present location, while increasingly influencing the path of Tropical Storm Francine. The 11Z surface analysis showed a wavy, quasistationary frontal zone fro Atlantic waters offshore SC, across northern FL to near the Mississippi River mouth, then a warm front arching across Gulf waters just south of the LA and TX Coasts, and into western parts of the Francine circulation. This boundary should move little from about 90W eastward, but remain a warm front over the upper TX and LA coastal waters, diffusely shifting inland over southern LA through the period. ...LA Coast... T.S. Francine -- initially centered southeast of BRO -- is forecast by NHC to turn northeastward across the northwestern Gulf today and become a hurricane, then move ashore in Louisiana on day 2. Suitably rich low-level moisture already is in place over coastal LA, and scattered to numerous showers and thunderstorms should cover the outlook area throughout much of the period, even well northeast of Francine's center. However, supercell potential will await sufficiently strong wind fields reaching the coastline ahead of the cyclone to enlarge hodographs favorably -- likely during the last few hours of the period. Then, tornado potential will be a matter of having relatively distinct/discrete, outer-band convection that can survive long enough to mature into supercells before weakening again in more-stable inflow air -- either inland or in broader precip areas. Unconditional probabilities are kept at marginal levels for now, given the late timing of the favorable kinematic fields, the nocturnal min in overland instability, and convective/ structural uncertainties with Francine. ..Edwards/Kerr.. 09/10/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0334 AM CDT Tue Sep 10 2024 Valid 131200Z - 181200Z ...DISCUSSION... Severe potential appears low through the period. Primary concern for D4/Friday is any lingering tornado threat associated with the remnants of TC Francine. It is forecast by NHC to drift into the Mid-South/MS Valley to Lower OH Valley vicinity. Latest guidance indicates further weakening of low-level wind fields on Friday, likely becoming inadequate to sustain a synoptically evident TC tornado threat. Beyond this time frame, a quiescent pattern for severe is expected this weekend into early next week. Towards mid-week, majority of ensemble guidance suggests potential large-scale amplification of an upper trough into the West. This may yield an increase of low-probability severe around D8 and beyond over parts of the Great Plains, where many preceding days of above-normal temps will occur. Read more