SPC AC 211604
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1004 AM CST Wed Feb 21 2018
Valid 211630Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY FROM EXTREME
SOUTHEAST TX TO NORTHEAST LA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS INTO EARLY
TONIGHT FROM SOUTHEAST TX TO CENTRAL MS...
Thunderstorms will continue from Texas today to the Ohio Valley and
Appalachians today into tonight, some of which will be associated
with freezing or frozen precipitation across northwest Texas and
Oklahoma. A couple of tornadoes and isolated strong wind gusts will
be possible with the storms across Louisiana and adjacent areas of
southeast Texas and west central Mississippi.
...Lower MS Valley and southern Plains through tonight...
A deep warm/moist conveyor belt is established from the western Gulf
of Mexico into the lower MS Valley, along and immediately southeast
of a slow-moving cold front. The pattern will change little through
tonight as the large-scale ridge persists over the southwest
Atlantic and at least two shortwave troughs continue to dig
southward/southeastward along the Pacific coast to maintain the mean
western trough. Within the warm conveyor belt, a maritime tropical
air mass (boundary layer dewpoints near 70 F) will continue to
spread northward across LA/MS today, with some surface heating
possible along the southeast periphery of the ongoing warm sector
convection. The storms are likely to persist through the day in
this moist and uncapped environment per regional 12z soundings,
where deep-layer vertical shear will be sufficient for supercells
within the larger storm clusters. Given the rich low-level moisture
and effective SRH in excess of 200 m2/s2, a couple of tornadoes will
be possible, along with isolated strong wind gusts.
Otherwise, a swath of elevated convection will continue above the
shallow cold air mass across the southern Plains. The boundary
layer will be sufficiently cold for a mix of sleet and freezing rain
with the elevated convection from northwest TX into southern OK
today through early tonight.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z