SPC AC 210821
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0221 AM CST Tue Feb 21 2017
Valid 231200Z - 241200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
Isolated thunderstorms are forecast across portions of the Midwest
primarily after sunset Thursday night into early Friday morning. A
few storms are possible along the east coast of Florida.
A large-scale mid-level trough will feature a broad belt of strong
cyclonic flow moving through its base from the Desert Southwest
through the central and southern Great Plains and into the Midwest
on Thursday. A shortwave disturbance is forecast to move from the
central Rockies into IA by early Friday morning. In the low levels,
a surface low will develop northeastward from the central High
Plains into the middle MS Valley coincident with the aforementioned
mid-level impulse. A warm front will extend eastward from the low
while a cold front moves southeast across KS and much of OK.
Elsewhere, a weak mid-level low will slowly meander to the east of
the FL peninsula.
...middle MS Valley...
Marginal low-level moisture over the Mid South and lower MS Valley
will advect northward during the day within the warm conveyer of the
central U.S. cyclone. Models suggest dewpoints ranging from 54-58
degrees F will reach the lower MO Valley and middle MS Valley region
by early evening. A southwesterly low level jet is forecast to
strengthen to 50+ kt after dark across MO/IL with a corresponding
increase in isentropic ascent. Showers and isolated thunderstorms
are forecast to develop primarily on and north of the warm front. A
cap will likely limit storm development southward over the Ozarks.
Although models show strong shear and marginally unstable profiles,
notable differences still exist amongst medium-range models on the
evolution of a mid-level vorticity maximum and surface low track
over the Midwest. Given the model variability and uncertainty
regarding convective evolution late in the Day 3 period, will defer
to later outlooks about the possible inclusion of low-severe
probabilities over a portion of this region.
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