SPC Sep 24, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0220 AM CDT Fri Sep 24 2021 Valid 261200Z - 271200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe storms are unlikely across the Lower 48 on Sunday. ...Synopsis and Discussion... The upper-air pattern will feature strong cyclonic flow from the Great Lakes into the Northeast, with an upper low moving from Lake Erie northeastward down the St. Lawrence Valley. Low pressure will develop over ME during the day, shifting into Canada after 00Z while deepening. A cold front will extend south from the low over the western Atlantic, curling westward across southern FL and becoming stationary over the central Gulf of Mexico. While early day showers and a few thunderstorms may occur over ME, instability is forecast to remain too weak for severe storms prior to frontal passage. To the west, a weaker upper low will drift east across the lower CO Valley, providing cool midlevel temperatures and modest southerly flow aloft over eastern AZ and western NM. Heating will result in MLCAPE near 1000 J/kg, and this may favor a few strong storms during the afternoon. Neither shear nor instability are expected to favor severe weather, although a few strong storms may yield small hail and gusty winds from AZ into western NM. ..Jewell.. 09/24/2021 Read more LIVE: spc.noaa.gov
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SPC Sep 24, 2021 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0725 PM CDT Thu Sep 23 2021 Valid 240100Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms will be possible this evening into tonight from parts of far eastern North Carolina north-northeastward into south-central New England. Isolated thunderstorms may also occur in parts of the Desert Southwest. No severe thunderstorms are expected this evening through tonight. ...DISCUSSION... An upper-level low will move northward across the northern Great Lakes tonight as a cold front advances eastward across the central Appalachians. Thunderstorms will be possible near and ahead of the front from coastal sections of eastern North Carolina north-northward into south-central New England. Isolated thunderstorms may also occur across parts of the Desert Southwest. Instability and deep-layer shear is not expected to be sufficient across the continental United States for severe weather through tonight. ..Broyles.. 09/24/2021 Read more LIVE: spc.noaa.gov
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SPC Sep 23, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0237 PM CDT Thu Sep 23 2021 Valid 232000Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN MID-ATLANTIC INTO SOUTHERN NEW ENGLAND... ...SUMMARY... Isolated strong to severe storms associated with a marginal threat for a brief tornado and occasional wind damage should continue today into tonight across parts of the Mid-Atlantic and southern New England. ...20Z Update... ...Mid-Atlantic into Southern New England... Forecast reasoning from the previous outlook (appended below) remains valid. Only change to the ongoing forecast was to trim up the western edge based on the current position of the front. Otherwise, occasional strong to damaging winds should be the main threat through the rest of the day as the band of convection develops slowly eastward towards the Atlantic Coast. ..Mosier.. 09/23/2021 .PREV DISCUSSION... /ISSUED 1125 AM CDT Thu Sep 23 2021/ ...Mid-Atlantic into Southern New England... A band of showers and storms is ongoing across parts of the Mid-Atlantic along and just ahead of a surface cold front. A zone of large-scale ascent associated with low-level warm advection and modest convergence along the front will continue through tonight, while making slow eastward progress as a closed upper low moves gradually northward across the Great Lakes region into southeastern Ontario. Low-topped convection should continue to train northward this afternoon and evening within the larger belt of precipitation across the Mid-Atlantic. The environment ahead of this activity should remain marginally favorable for isolated strong to severe storms. Visible satellite imagery shows a fair amount of cloud cover ahead of the line, which should slow diurnal heating and steepening of low-level lapse rates though the afternoon. Still, a moist low-level airmass characterized by mid 60s to low 70s surface dewpoints combined with modest diabatic heating should support generally 500-1250 J/kg of MLCAPE, with greater instability across DE/NJ compared to southern NY and vicinity. The strongest and largely meridional winds are expected to remain behind the surface cold front, with only about 30-35 kt of deep-layer shear present across the warm sector. Even so, some enhancement to the low-level wind field is present ahead of the band of storms, and a brief embedded circulation capable of producing a tornado or two remains possible. Otherwise, occasional strong to damaging winds should be the main threat through the rest of the day as the band of convection develops slowly eastward towards the Atlantic Coast. This marginal severe threat may continue through tonight across parts of southern New England where sufficient boundary-layer moisture can support weak instability and the potential surface-based storms. Read more LIVE: spc.noaa.gov
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