Day 1 Severe Weather Outlook

Valid 121300Z – 131200Z


Scattered damaging winds and a few tornadoes will be possible
beginning around 3 PM in Mississippi, spreading east-northeast
across parts of Alabama and Tennessee into the southern Appalachians
through tonight.

…MS/AL/TN vicinity…
No appreciable change to Slight Risk area after a series of prior
contractions. The degree of instability is the primary limiting
factor and driver of uncertainty for a high shear/low CAPE event.

A shortwave trough over Chihuahua and the TX Trans-Pecos will eject
northeast towards the Mid-South tonight, largely becoming absorbed
by an amplifying longwave trough in the north-central states. A
surface cyclone over Greater Houston will deepen as it rapidly
tracks towards eastern KY by late evening. A west/east-oriented warm
front along the central Gulf Coast will advance northeast towards
the southern Appalachians, while a cold front trails to the
southwest of the surface low.

Upper 60s surface dew points will spread northeast in the warm
sector across LA into central MS, with lower to mid 60s expected
with northeast extent given the current presence of a modified CP
air mass north of the front. The RAP appears more aggressive with
boundary-layer moisture return compared to the ECMWF/NAM/GFS. Poor
mid-level lapse rates will curtail instability and suggest that at
least low 60s surface dew points will be necessary for scant
surface-based buoyancy. MLCAPE should predominately increase to only
250-750 J/kg, with around 1000 J/kg confined to southern LA and
southwest MS.

Convective development along the cold front is expected around 21Z
in the Ark-La-Miss vicinity near and just southwest of the surface
low. With the deep-layer shear vector largely paralleling the front,
convection will likely grow upscale into a fast-moving QLCS that
rapidly progresses across the TN Valley this evening. Within a belt
of 60-80 kt 700-mb winds, a risk for strong to isolated severe wind
gusts should accompany the QLCS despite the weak instability. This
may yield scattered damaging winds over parts of northeast MS,
northern AL, and middle/eastern TN before the QLCS weakens overnight
across the southern Appalachians. A few embedded tornadoes are also
possible given enlarged low-level hodographs in the warm sector.

..Grams/Mosier.. 02/12/2020


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