SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0639 AM CST Tue Feb 09 2021

Valid 091300Z - 101200Z


Severe thunderstorms are not forecast through tonight across the
contiguous United States.

In mid/upper levels, a large, complex cyclone will remain over
central Canada through the period, helping to maintain broadly
cyclonic to zonal flow across most of the CONUS.  Moisture-channel
imagery indicates a lengthy but weak, strongly positively tilted
perturbation from northern GA southwestward across deep south TX and
northeastern MX.  The northern portion of this perturbation will
move offshore from the GA coastline by 18Z, with a weaker, trailing
vorticity banner across northern FL and the northeastern Gulf. 
Farther west, a better-defined/southern-stream trough was apparent
over the Pacific west of CA and Baja, roughly between 125W-130W. 
This feature should amplify somewhat and reach southern CA and
northwestern Baja by the end of the period, but with insufficient
levels of both lift and low-level theta-e resulting in lack of
overland thunder potential. 

At the surface, 11Z analysis showed a frontal-wave low just offshore
from PNS, with slow-moving cold front west-southwestward across the
extreme northern Gulf, becoming quasistationary and diffuse over
south TX.  An intense, reinforcing cold front was analyzed from the
Arklatex region across central TX to the Edwards Plateau, becoming
quasistationary over eastern NM.  The northeastern Gulf low will
weaken near the west-central FL Panhandle coastline while another
develops offshore from GA.  The front should move little across the
northern Gulf, pending being overtaken by the stronger front after
this period.  A warm front -- extending from the Gulf low east-
southeastward across the northern FL Peninsula -- may reach the
FL/GA line before this evening, then become quasistationary behind
the Atlantic low. 

Widely scattered to scattered thunderstorms are ongoing across
portions of southern AL, southwestern GA and the FL Panhandle.  This
convection is rooted in a layer of elevated inflow of sufficiently
modified Gulf air, lifted above the relatively stable near-surface
layer north of the front.  The supportive zone of warm advection and
moisture transport is expected to shift eastward across GA and
northern FL through today, weakening with time as the related
midlevel perturbation moves away.  However, in the meantime, bands
of thunderstorms will continue to shift eastward over the outlook
area, amidst MUCAPE in the 500-1000 J/kg range.  Nearly surface-
based parcels near the warm front may brush the immediate coastal
area roughly between PAM-AAF in the next few hours before the bulk
of convection passes the area, so locally strong nearshore gusts are

Latest objectively analyzed/RAP-based mesoanalysis data and forecast
soundings through midday indicate 45-60-kt effective-shear
magnitudes, amidst sufficiently steep midlevel lapse rates to
support hail approaching severe limits with the most intense cells. 
While very isolated, brief, marginally severe hail cannot be ruled
out, the threat still appears too conditional and sparse to warrant
5%+ probabilities that would trigger a categorical outlook area.

..Edwards.. 02/09/2021

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