Day 1 Severe Weather Outlook

Valid 051200Z – 061200Z


Scattered severe thunderstorms are expected today and tonight across
the lower Mississippi Valley and Southeast states. Damaging wind
gusts and a few tornadoes may accompany the more intense storms.

Recent satellite imagery shows a deep upper trough extending from
the central High Plains southwestward into the central Baja
Peninsula. A shortwave trough embedded within this larger system —
currently moving into northwest Mexico — is expected to eject
eastward/northeastward across the southern Plains and into the mid
MS Valley today. As it does, the parent upper trough will trend
toward a more neutral tilt and southwesterly flow aloft will
increase from south TX into the middle OH Valley. By early Thursday
morning, 500-mb winds over 100 kt are anticipated from the Mid-South
into IN/OH.

At the surface, the cold front currently extending from a low just
west of BNA southwestward to the TX Hill Country will continue
gradually southward/southeastward over the next few hours. However,
progression across the Lower MS Valley and Southeast is expected to
slow as cyclogenesis occurs over central LA and mass response
increases within the warm sector. This will result in a sharpening
of the temperature/dewpoint gradient along the boundary during the
afternoon before the low then progresses quickly northeastward along
the front, reaching middle TN by late Wednesday evening and eastern
KY by early Thursday morning.

Ascent associated with the approaching shortwave trough as well as
near the surface low and along its attendant cold front will
contribute to thunderstorm development across much of the Lower MS
Valley and Southeast on Wednesday.

…Lower MS Valley…Southeast…
A somewhat complex scenario expected across the region today.
Widespread cloudiness and showers will likely temper daytime
heating, keeping temperatures in the upper 60s/low 70s. Modest
low-level moisture is already in place but the anticipated mass
response could contribute to a further increase. However, the
strength of this potential moisture increase is predicated on the
intensity/coverage of any upstream convection along the coast.
Current expectation is for the bulk of the coastal convection to
occur across southern AL/MS and the western FL Panhandle.

This leaves the potential for moisture advection across AL and MS,
which could occur amidst backing surface winds and strengthening low
to mid-level winds. Consequently, a corridor of slightly higher
severe risk may materialize from far northeast LA across central MS
into far west-central AL, near the track of surface low. However,
even with this anticipated moisture advection, instability will be
limited by poor lapse rates resulting from relatively warm mid-level
temperatures. Instability is expected to be the limiting factor,
given that vertical shear throughout the warm sector will be more
than sufficient for storm organization/rotation. Uncertainty
regarding instability as well as questions concerning the position
of the front and any effects of antecedent precipitation preclude
introducing higher severe probabilities with this outlook.

Current expectation is for thunderstorm coverage to begin increasing
during the early afternoon, becoming widespread by 00Z Thursday.
Damaging wind gusts within the bowing line segments along and just
ahead of the front will be the primary severe risk. A few tornadoes
are also possible, particularly within the corridor mentioned above
where mesoscale ascent will augment large-scale forcing and surface
winds will be more backed.

..Mosier/Bentley.. 02/05/2020


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