Day 1 Severe Weather Outlook

Valid 121630Z – 131200Z

…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH LATE EVENING FROM CENTRAL MS TO NORTHERN AL/SOUTHEASTERN
TN/NORTHWESTERN GA…

…SUMMARY…
A few damaging gusts and a couple of tornadoes will be possible
beginning mid afternoon across Mississippi and continuing into
northern Alabama and southeastern Tennessee through late evening.

…MS this afternoon to TN this evening…
No changes to the previous outlook area. A midlevel shortwave
trough over the southern Plains this morning will accelerate
east-northeastward and lose amplitude through the period, as a
primary northern stream trough amplifies over the upper
Midwest/Great Lakes, and a subtropical ridge persists over FL. The
ejecting trough will glance the northwest edge of the surface warm
sector today, with weak cyclogenesis expected along a baroclinic
zone from the ArkLaMiss this afternoon to the TN Valley this evening
and the Appalachians overnight.

Low-level moisture will spread inland rather quickly today in
advance of the developing surface cyclone, with boundary-layer
dewpoints in the 60s expected as far north and southern middle TN by
this evening. However, regional 12z soundings revealed poor lapse
rates below relatively warm temperatures near 600 mb (associated
with the subtropical ridge). Surface heating will also be limited
by clouds (aside from possibly southeast LA into southwest MS).
Thus, narrow CAPE profiles (MLCAPE 250-500 J/kg) are expected in an
environment with otherwise increasing low-level and deep-layer
vertical shear beginning this afternoon across MS and spreading into
the TN Valley this evening. The poor lapse rates/weak buoyancy
suggest it will be difficult to form and sustain warm-sector
supercells this afternoon, and the majority of the deeper convection
should be confined to the track of the surface low and trailing cold
front from mid afternoon into early tonight. Since convection will
tend toward a linear mode along the front, the main threat should be
damaging winds and perhaps a couple of tornadoes with embedded
circulations. Lingering frontal convection will likely weaken
overnight toward the southern Appalachians.

..Thompson/Squitieri.. 02/12/2020

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