SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

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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