SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1159 PM CST Sun Feb 21 2021 Valid 221200Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are possible across southeast Georgia and much of Florida as well as the immediate North Carolina coast this afternoon/evening. Severe thunderstorms are not expected. ...Synopsis... A progressive upper trough and associated 150 kt 300 mb jet streak will overspread the eastern CONUS through the day. Very strong deep-layer wind fields are expected to precede the upper trough axis and an approaching surface cold front during the afternoon hours across portions of the Mid Atlantic southward to the Carolina coastal areas. Along the immediate coastline, a modified marine layer may promote very modest low-level buoyancy, potentially supporting deep enough moist convection to foster a few lightning flashes. Farther south across southern GA into FL, forcing for ascent will be weaker as the upper trough is expected to remain mainly north of the area. However, more appreciable instability will be in place, with isolated thunderstorm development possible along a weak but broad confluence zone ahead of a southward sagging cold front. ...Portions of the immediate Atlantic Seaboard... While most of the convection across the Mid Atlantic is expected to remain low-topped in nature given lack of buoyancy, latest CAM guidance depicts a well-defined line of showers developing along a strong confluence zone ahead of the cold front. Given the very strong flow fields associated with these showers (i.e 850 mb winds exceeding 60 kts beneath 100+ kts at 500 mb), any dynamically driven downward momentum transport may support strong to potentially damaging gusts. At the moment, greater buoyancy appears to reside just offshore, with a stronger convective squall line likely developing after the line of showers moves offshore. Given the lack of greater onshore instability to support lightning flash potential/thunderstorm development, severe probabilities have not been added at this time. CAM guidance consensus depicts the line of showers developing around 18Z (1 PM EST) across southeast VA into northern NC an exiting the coastline around 21-22Z (4-5 PM EST). ..Squitieri.. 02/22/2021
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