SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1027 AM CST Wed Nov 25 2020

Valid 251630Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH LATE EVENING FROM SOUTHEAST LA TO PARTS OF AL/NORTHWEST
GA...AND ACROSS THE LOWER OH VALLEY...

...SUMMARY...
Isolated damaging winds and a tornado or two will be possible this
afternoon trough late evening from southeast Louisiana to central
Alabama and northwest Georgia, and across the lower Ohio Valley.

...Lower OH Valley this afternoon/evening...
A midlevel shortwave trough over MO will continue east-northeastward
to the upper OH Valley overnight.  A surface cyclone near Saint
Louis will likewise move east-northeastward toward Lake Erie, and
both the midlevel trough and cyclone are expected to weaken
gradually by tonight.  A narrow zone of surface
heating/destabilization and boundary-layer dewpoints in the upper
50s is expected this afternoon from southern IL into southwestern IN
and western KY, southeast of the surface cyclone.  Though
surface-based buoyancy will remain weak, vertical shear will be
favorable for a low-end threat of low-topped supercells or short
line segments capable of producing isolated damaging winds and
perhaps a tornado.

...Southeast LA to central AL/northwest GA through late evening...
Farther south, a pre-frontal squall line is moving eastward across
southeast LA, central MS, and northwestern AL.  The influence of
this ongoing convection will likely limit the potential for
destabilization this afternoon, immediately to its north into TN. 
The ongoing convective band will shift slowly eastward, with some
low-level moistening/destabilization possible into central AL. 
Deep-layer and low-level vertical shear/SRH will tend to weaken
through the day from southwest-to-northeast as the primary synoptic
wave passes to the north over the OH Valley.  Still, some low-end
potential will remain for line segments and embedded supercells
capable of producing isolated damaging winds and a tornado or two.

..Thompson/Wendt.. 11/25/2020

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