SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0121 PM CST Thu Dec 12 2024 Valid 122000Z - 131200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Lightning is possible this evening and tonight along the eastern shores of Lake Ontario in association with lake-effect snow bands. ...20Z Update... The forecast remains on track, and no changes were made with this update. See the previous discussion below for details regarding isolated lightning potential downwind of Lake Ontario. ..Weinman.. 12/12/2024 .PREV DISCUSSION... /ISSUED 1016 AM CST Thu Dec 12 2024/ ...NY... Cool/dry and stable conditions will prevail over the most of the CONUS today, with no organized thunderstorm activity expected. One exception will be in the vicinity of the eastern shores of Lake Ontario (Jefferson/Lewis/Oswego counties). A long-fetch lake-effect snow band is forecast to develop later this evening and tonight. Forecast soundings suggest a sufficiently deep convective layer to promote charge separation and a few lightning strikes - mainly after 02z. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0121 PM CST Thu Dec 12 2024 Valid 122000Z - 131200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Lightning is possible this evening and tonight along the eastern shores of Lake Ontario in association with lake-effect snow bands. ...20Z Update... The forecast remains on track, and no changes were made with this update. See the previous discussion below for details regarding isolated lightning potential downwind of Lake Ontario. ..Weinman.. 12/12/2024 .PREV DISCUSSION... /ISSUED 1016 AM CST Thu Dec 12 2024/ ...NY... Cool/dry and stable conditions will prevail over the most of the CONUS today, with no organized thunderstorm activity expected. One exception will be in the vicinity of the eastern shores of Lake Ontario (Jefferson/Lewis/Oswego counties). A long-fetch lake-effect snow band is forecast to develop later this evening and tonight. Forecast soundings suggest a sufficiently deep convective layer to promote charge separation and a few lightning strikes - mainly after 02z. Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1111 AM CST Thu Dec 12 2024 Valid 131200Z - 141200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not expected through Friday night. ...Central States... A shortwave trough near the Four Corners will move across the southern Rockies into the central Great Plains by early Saturday. The attendant lee surface cyclone will be weak as it tracks from the Raton Mesa vicinity into eastern KS. Modified moisture return from the western Gulf is anticipated within the broad low-level warm conveyor ahead of the minor cyclone. Adequate buoyancy in conjunction with timing of forcing for ascent attendant to the shortwave trough should yield a pronounced increase in elevated convection Friday night into early morning Saturday from the Red River Valley towards the Lower MO Valley. Steeper mid-level lapse rates will be confined to the north side of the mid-level jet in OK to eastern KS. Weak mid-level lapse rates (around 6 C/km) will curtail elevated buoyancy where low-level moisture progressively increases with southern extent. Still, favorable veering of the wind profile with height could yield transient, weak mid-level updraft rotation across parts of east TX to the southern Ozarks. Small hail may occur within the deepest updrafts, with large hail probabilities appearing to be sub-5 percent. ...Northern CA... A pair of shortwave troughs in the northeast Pacific will approach the West Coast. The southern one of these should remain offshore of the northern CA coast through 12Z Saturday. The downstream low-level warm conveyor will yield a swath of rain ahead of a weak cold front. Sufficient low-level moistening, along with some mid-level cooling with the approaching trough, may support scant buoyancy by 09-12Z. Overall thunderstorm probabilities early Saturday morning appear to be around 10 percent near a portion of the northern CA coast. ..Grams.. 12/12/2024 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1103 AM CST Thu Dec 12 2024 Valid 121700Z - 131200Z ...NO CRITICAL AREAS... No changes are needed to the D1 Fire Weather Outlook. See previous discussion for more information. ..Thornton.. 12/12/2024 .PREV DISCUSSION... /ISSUED 1242 AM CST Thu Dec 12 2024/ ...Synopsis... Fire weather concerns may emerge across parts of the southern Plains and Southwest this afternoon; however, relatively moist fuel conditions continue to limit the overall fire threat. Early-morning water vapor imagery depicts a slowly de-amplifying ridge from the southern Rockies into western Canada with shortwave troughs approaching the Pacific Northwest and Baja California. These upper waves will drive fire weather concerns for the next two days as they migrate east into the Southwest and southern Plains. ...Central TX into OK... A modest, southerly, dry return-flow regime is becoming established over the southern Plains as a surface high over the lower MS River Valley gradually shifts east. Additionally, a weak lee cyclone is noted in surface observations across eastern CO. Over the next 12-24 hours, the low-amplitude upper wave approaching Baja California will overspread the southern Rockies, resulting in a gradual intensification of the lee cyclone. As a result, southerly winds should increase to 15-20 mph across central TX into southern and central OK. The recent deep frontal intrusion across the Gulf will limit moisture recovery with RH minimums around 20% expected this afternoon. While elevated (to perhaps locally critical) fire weather conditions are possible, recent fuel guidance suggests ERCs are well below the 50th percentile. Consequently, fire concerns should remain limited to primarily finer fuel beds that may see sufficient drying by late afternoon to support fire spread. ...Arizona... 06 UTC surface observations show very dry conditions across southern CA into southern AZ with RH values in the single digits to low teens. This dry air mass will spread north through the day as surface pressure falls across NV/UT in response to the approach of the upper wave off the Pacific Northwest coast. Afternoon RH minimums in the single digits are anticipated, and may coincide with 15 mph winds - especially along and north of the Mogollon Rim. However, as with the southern Plains, ERC guidance suggests fuels are not overly receptive at this time, which precludes highlights. ...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 1016 AM CST Thu Dec 12 2024 Valid 121630Z - 131200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Lightning is possible this evening and tonight along the eastern shores of Lake Ontario in association with lake-effect snow bands. ...NY... Cool/dry and stable conditions will prevail over the most of the CONUS today, with no organized thunderstorm activity expected. One exception will be in the vicinity of the eastern shores of Lake Ontario (Jefferson/Lewis/Oswego counties). A long-fetch lake-effect snow band is forecast to develop later this evening and tonight. Forecast soundings suggest a sufficiently deep convective layer to promote charge separation and a few lightning strikes - mainly after 02z. ..Hart.. 12/12/2024 Read more

MD 2262 CONCERNING HEAVY SNOW FOR PARTS OF WESTERN NY/EXTREME NORTHWEST PA DOWNSTREAM OF LAKE ERIE
Mesoscale Discussion 2262 NWS Storm Prediction Center Norman OK 0939 AM CST Thu Dec 12 2024 Areas affected...Parts of western NY/extreme northwest PA downstream of Lake Erie Concerning...Heavy snow Valid 121539Z - 121845Z SUMMARY...Very heavy snow rates will continue in the short term, with some weakening possible by early afternoon. DISCUSSION...An intense lake-effect snow band is ongoing this morning across parts of western NY and extreme northwest PA, downstream of Lake Erie. Recent reports suggest snow rates in excess of 3 inches per hour in the heaviest part of the band, with one report of 12 inches over a 2 hour span in Erie County, NY. These very heavy snow rates will persist in some areas through the remainder of the morning. In addition, wind gusts of 30-45 kt have been noted across the region this morning, resulting in occasional blizzard conditions. A notable shortwave trough embedded in deep cyclonic flow is currently moving east of Lake Huron and approaching the lower Great Lakes region. Low-level flow response to this shortwave could result in some disruption of the ongoing snow band by early afternoon, and short-term guidance (including the 12Z CAMs) generally suggest the band will tend to drift south and at least temporarily weaken by early afternoon. ..Dean.. 12/12/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BUF...CLE... LAT...LON 42227920 42117968 41998025 42058034 42178032 42278001 42427966 42867843 42907805 42687814 42367878 42227920 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0617 AM CST Thu Dec 12 2024 Valid 121300Z - 131200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms appear unlikely through tonight. ...Synopsis/Discussion... A mid/upper-level cyclone -- initially over northern ON -- will break down as another develops across central QC today, within the same larger-scale troughing regime. As the resulting low ejects northeastward over northern QC, and synoptic ridging moves from the Rockies to the Plains States, heights will rise over most of the central/eastern CONUS. The air mass east of the Rockies mostly will remain too dry and/or stable for thunderstorms, behind the cold frontal passage related to the departing eastern trough. One exception may be in the lake-effect regimes east of the lower Great Lakes, where steep low/middle-level lapse rates will support plumes of heavy convective snow. However, shallowness of buoyancy/ELs precludes more than very brief/isolated lightning potential at most, and the threat appears too conditional and limited for outlook areas. A cyclone now located off the coast of OR and northwestern CA will move inland and devolve slightly to a strong shortwave trough, reaching northern CA and western/southern NV by 00Z. By 12Z, the trough will reach southern ID, UT and AZ. Strong DCVA/cooling aloft is expected immediately to its east today and tonight, from the Great Basin to the Colorado Plateau and UT/southwestern WY. However, with dry air in low levels over most of the region, midlevel moisture/buoyancy should remain too weak and isolated for enough lightning to justify an outlook area. ..Edwards/Jewell.. 12/12/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0617 AM CST Thu Dec 12 2024 Valid 121300Z - 131200Z ...NO THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms appear unlikely through tonight. ...Synopsis/Discussion... A mid/upper-level cyclone -- initially over northern ON -- will break down as another develops across central QC today, within the same larger-scale troughing regime. As the resulting low ejects northeastward over northern QC, and synoptic ridging moves from the Rockies to the Plains States, heights will rise over most of the central/eastern CONUS. The air mass east of the Rockies mostly will remain too dry and/or stable for thunderstorms, behind the cold frontal passage related to the departing eastern trough. One exception may be in the lake-effect regimes east of the lower Great Lakes, where steep low/middle-level lapse rates will support plumes of heavy convective snow. However, shallowness of buoyancy/ELs precludes more than very brief/isolated lightning potential at most, and the threat appears too conditional and limited for outlook areas. A cyclone now located off the coast of OR and northwestern CA will move inland and devolve slightly to a strong shortwave trough, reaching northern CA and western/southern NV by 00Z. By 12Z, the trough will reach southern ID, UT and AZ. Strong DCVA/cooling aloft is expected immediately to its east today and tonight, from the Great Basin to the Colorado Plateau and UT/southwestern WY. However, with dry air in low levels over most of the region, midlevel moisture/buoyancy should remain too weak and isolated for enough lightning to justify an outlook area. ..Edwards/Jewell.. 12/12/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0320 AM CST Thu Dec 12 2024 Valid 151200Z - 201200Z ...DISCUSSION... Most of the medium-range guidance has trend faster and less amplified with the shortwave trough expected to move from the Four Corners region through the central Plains on D4/Sunday. This more northerly progression will limit the interaction between this wave and any returning low-level moisture, which should limit thunderstorm potential throughout most of the day. Another shortwave trough is expected to follow in the wake of this lead wave, but with a more southerly track across the Southwest and into the southern Plains. Guidance is in relatively good agreement that this wave will move over the southern High Plains late D4/Sunday into early D5/Monday. This wave is expected to interact with the returning low-level moisture, with thunderstorm development along and ahead of its associated front from central OK/north TX into the Ozarks early Monday morning. Thunderstorms are expected to gradually shift eastward throughout the day D5/Monday, expanding into more of east/southeast TX and the Mid/Lower MS Valley. Seasonally warm and moist conditions are anticipated, and enough buoyancy and shear could be in place for severe thunderstorms. However, overall buoyancy will likely be mitigated by poor lapse rates, and warm mid-level temperatures could contribute to some inhibition. There is also some potential for a more front-parallel orientation, which could result in a more anafrontal character to the storms. These factors, combined with the notable variability within the guidance, introduce enough uncertainty to merit withholding any severe probabilities for D4/Sunday or D5/Monday with this outlook. Another shortwave trough may progress into the Plains on D7/Wednesday, with preceding moisture return across the southern Plains setting up the potential for thunderstorms as this wave and its associated cold front push eastward/southeastward across the southern Plains. However, GEFS members show large differences on how this wave progresses, with notable differences within the ECMWF members too. Some members within both of these ensemble systems suggest the development of a closed low over the Southwest instead of progressive wave into the Plains. Consequently, as with the earlier wave, predictability issues limit forecast confidence. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0320 AM CST Thu Dec 12 2024 Valid 151200Z - 201200Z ...DISCUSSION... Most of the medium-range guidance has trend faster and less amplified with the shortwave trough expected to move from the Four Corners region through the central Plains on D4/Sunday. This more northerly progression will limit the interaction between this wave and any returning low-level moisture, which should limit thunderstorm potential throughout most of the day. Another shortwave trough is expected to follow in the wake of this lead wave, but with a more southerly track across the Southwest and into the southern Plains. Guidance is in relatively good agreement that this wave will move over the southern High Plains late D4/Sunday into early D5/Monday. This wave is expected to interact with the returning low-level moisture, with thunderstorm development along and ahead of its associated front from central OK/north TX into the Ozarks early Monday morning. Thunderstorms are expected to gradually shift eastward throughout the day D5/Monday, expanding into more of east/southeast TX and the Mid/Lower MS Valley. Seasonally warm and moist conditions are anticipated, and enough buoyancy and shear could be in place for severe thunderstorms. However, overall buoyancy will likely be mitigated by poor lapse rates, and warm mid-level temperatures could contribute to some inhibition. There is also some potential for a more front-parallel orientation, which could result in a more anafrontal character to the storms. These factors, combined with the notable variability within the guidance, introduce enough uncertainty to merit withholding any severe probabilities for D4/Sunday or D5/Monday with this outlook. Another shortwave trough may progress into the Plains on D7/Wednesday, with preceding moisture return across the southern Plains setting up the potential for thunderstorms as this wave and its associated cold front push eastward/southeastward across the southern Plains. However, GEFS members show large differences on how this wave progresses, with notable differences within the ECMWF members too. Some members within both of these ensemble systems suggest the development of a closed low over the Southwest instead of progressive wave into the Plains. Consequently, as with the earlier wave, predictability issues limit forecast confidence. Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0219 AM CST Thu Dec 12 2024 Valid 141200Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated thunderstorms are possible from the Texas Hill Country into the Middle/Lower Mississippi Valley on Saturday. ...Synopsis and Discussion... A stacked mid-latitude cyclone is forecast to be over the central Plains early Saturday morning before progressing northeastward throughout the day and ending the period over the Mid MS Valley. This cyclone will be accompanied by strong mid-level jet throughout its base, which will spread from OK northeastward across MO and into the Lower OH Valley as the cyclone moves northeastward. This overall evolution will displace this cyclone and associated ascent well north of the better low-level moisture, which is expected to remain confined largely to the TX and LA coasts throughout the day. Even so, a strong low-level jet is anticipated throughout the warm sector of this cyclone, and the associated warm-air advection will likely result in elevated showers and thunderstorms. Elevated thunderstorms will likely be ongoing at the beginning of the period from east TX into the Lower MO Valley. This is area expected is shift eastward throughout the day with gradually diminishing storm coverage. Limited buoyancy should temper updraft strength, but vertical shear is strong enough to support small-hail production within the deepest, most persistent updrafts. An additional northwestward push of greater low-level moisture into more of the TX Hill Country is possible late Saturday/early Sunday ahead of another shortwave trough approaching the Four Corners. A few isolated thunderstorms may occur over the TX Hill Country as this returning moisture interacts with increasing low-level flow. ..Mosier.. 12/12/2024 Read more

SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0219 AM CST Thu Dec 12 2024 Valid 141200Z - 151200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Isolated thunderstorms are possible from the Texas Hill Country into the Middle/Lower Mississippi Valley on Saturday. ...Synopsis and Discussion... A stacked mid-latitude cyclone is forecast to be over the central Plains early Saturday morning before progressing northeastward throughout the day and ending the period over the Mid MS Valley. This cyclone will be accompanied by strong mid-level jet throughout its base, which will spread from OK northeastward across MO and into the Lower OH Valley as the cyclone moves northeastward. This overall evolution will displace this cyclone and associated ascent well north of the better low-level moisture, which is expected to remain confined largely to the TX and LA coasts throughout the day. Even so, a strong low-level jet is anticipated throughout the warm sector of this cyclone, and the associated warm-air advection will likely result in elevated showers and thunderstorms. Elevated thunderstorms will likely be ongoing at the beginning of the period from east TX into the Lower MO Valley. This is area expected is shift eastward throughout the day with gradually diminishing storm coverage. Limited buoyancy should temper updraft strength, but vertical shear is strong enough to support small-hail production within the deepest, most persistent updrafts. An additional northwestward push of greater low-level moisture into more of the TX Hill Country is possible late Saturday/early Sunday ahead of another shortwave trough approaching the Four Corners. A few isolated thunderstorms may occur over the TX Hill Country as this returning moisture interacts with increasing low-level flow. ..Mosier.. 12/12/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0108 AM CST Thu Dec 12 2024 Valid 131200Z - 141200Z ...Synopsis... Fire weather concerns are expected to emerge across the southern High Plains on Friday afternoon as a progressive upper wave traverses the southern Rockies. Recent water-vapor imagery depicts an upper wave off the coast of the Pacific Northwest. This feature is expected to reach central NM by around peak heating on Friday. In response to the arrival of the wave, an antecedent lee cyclone across east/southeast CO will intensify with an attendant low-level wind response. Recent ensemble guidance shows a strong signal for sustained 20 mph winds across eastern NM into parts of the northwestern TX Panhandle. The typically drier/windier deterministic solutions hint that sustained winds up to 25 mph (gusting to 35-40 mph) are possible, and this appears reasonable given the favorable timing of peak heating with the passage of a 40-50 knot 700 mb jet. The downslope flow regime should promote RH reductions well into the low teens, and possible into the single digits for some locations. As such, widespread elevated to critical fire weather conditions appear likely. The primary modulating factor is fuel status, which appears unfavorable for fire spread based on recent ERC/fuel guidance. However, finer 1-hour grasses may see sufficient drying to support a fire concern for some areas. ..Moore.. 12/12/2024 ...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 1255 AM CST Thu Dec 12 2024 Valid 131200Z - 141200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not expected through Friday night. ...Synopsis... A shortwave trough is forecast to begin the period over the Four Corners before continuing eastward across the central Rockies and ending the period as a closed cyclone over the central Plains. An associated surface low is expected to move quickly northeastward just ahead of this shortwave, progressing from the northeast NM/southeast CO vicinity into eastern KS. As it does, an attendant cold front will push eastward across the southern High Plains and western KS. Modified moisture return is anticipated within the strong low to mid-level flow preceding this shortwave and its attendant cold front. Low 60s dewpoints will likely reach north Texas by early Saturday morning but the mid 60s dewpoints are expected to remain confined to the TX Coastal Plain. A strengthening low-level jet and associated warm-air advection over the pre-frontal warm sector (from southeast TX into the Lower MO Valley) is forecast to result in elevated thunderstorms from Friday evening through Saturday morning. Poor lapse rates will limit buoyancy, with the expectation that most updrafts will be weak and transient. Strong vertical shear (i.e. 0-6 km bulk shear around 50 kt) may support small hail within the deepest, most persistent updrafts. ..Mosier.. 12/12/2024 Read more