Day 1 Severe Weather Outlook

Valid 161200Z – 171200Z


Scattered severe thunderstorms are forecast beginning midday today
over Louisiana and peaking during the late afternoon/evening from
northeast Louisiana into central Mississippi and into Alabama late.
A few tornadoes and damaging gusts are the primary hazards.

…Lower MS Valley into the TN Valley…
A mid-level shortwave trough near the TX-OK Panhandles this morning
will slightly weaken as it moves to the lower MO Valley by early
Tuesday morning. A surface front extending from east TX
northeastward into the lower TN Valley is forecast to sag south/east
through the lower MS Valley and into AL. A weak area of low
pressure is forecast to develop over northern LA by early afternoon
and migrate northeast into TN after dusk.

Sunday night surface observations over the northwest Gulf Coast
indicate a very moist airmass (dewpoints near 70 degrees F) has
infiltrated the coastal plain of the upper TX coast and southwest
LA. A relatively pristine convective scenario is forecast to unfold
beginning by the late morning-midday timeframe in the vicinity of
the Sabine Valley and gradually spread northeast during the
afternoon as the boundary layer destabilizes. The combination of
diurnal heating and continued moistening at the base of a weakening
capping inversion will gradually lead to convective development by
early afternoon. It appears thunderstorms will preferentially favor
the front but discrete warm sector initiation appears plausible
mainly in a corridor from central into northeast LA. Strong and
veering low- to mid-level flow fields are forecast across the
Enhanced Risk. Forecast hodographs show some tendency for some
minor veer-back-veer structure around 700mb which may dampen a more
favorable hodograph/storm rotation potential. Nonetheless, forecast
soundings show a moist boundary layer with MLCAPE ranging from 1500
J/kg across LA into central MS with decreasing CAPE with
northeast/east extent. Consequently, a fanning of lower severe
probabilities are forecast from north-central MS northeastward into
TN and the northern half of AL.

Large hail may accompany the stronger cores where the risk for
discrete updrafts is highest and where 700-500mb lapse rates are 7-8
degrees C/km over LA and parts of MS. The tornado risk will
probably maximize during the afternoon/evening over LA as
quasi-discrete activity develops and moves northeast into MS. A
gradual consolidation/merging of storms will lead to the risk for
damaging gusts increasing concurrent with upscale growth.

..Smith/Bentley.. 12/16/2019


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