...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
OH VALLEY INTO WESTERN TN AND NORTHEAST MS...
...SUMMARY...
Severe thunderstorms capable of tornadoes, large hail, and damaging
gusts are possible across portions of the Mid South today through
the early evening. A strong tornado is possible from the confluence
of the Ohio and Mississippi Rivers southward into parts of northern
Mississippi and northwest Alabama.
...Synopsis...
A vigorous, negatively tilted mid-level shortwave trough will move
from the central/southern Great Plains to the lower MO Valley by mid
afternoon and subsequently into the Great Lakes after dark. An
intense 90kt 500mb speed max will translate east-northeast from OK
into the lower OH Valley by early evening. In the low levels, a
surface low will develop northeast from central KS to the IA/IL/MO
border by 6pm and into the central Great Lakes overnight. A warm
front over the Mid South will advance northward into the lower OH
Valley by peak heating and a composite dryline/Pacific front will
arc south-southeast from the low into eastern AR and southwestward
into east TX by mid afternoon before sweeping east across the OH
Valley late.
...Eastern OK/TX into the mid-MS/lower OH Valleys...
A complex forecast scenario with associated uncertainty
appropriately describes the risk for severe thunderstorms and
possible tornadoes across portions of the Mid South into the lower
OH Valley today. At the start of the period, a couple of clusters
of strong to severe thunderstorms are forecast across western
portions of the larger-risk area in parts of northeast TX into
eastern OK/western AR. Varying possible solutions are evident in
model data whether all or parts of this activity moves downstream
with intermittent intensification into the MS Valley during the day
or whether some of this activity weakens on the southern portion
near the Ark-La-Tex during the late morning. Hail, wind, and
perhaps a tornado or two are possible with the early-day storms over
the Ark-La-Tex vicinity.
Farther east, an adequately moist/destabilizing warm sector will
spread north and northeast in wake of the warm front with surface
dewpoints ranging from near 60 degrees F in the lower OH Valley to
the middle 60s farther south into TN/AR/MS/AL. Model guidance
correspondingly indicates weaker buoyancy will exist farther north
(MLCAPEs at or below 500 J/kg north of the OH river to 750-1250 J/kg
farther south) but extreme low-level shear. Hodographs become very
large by early-mid afternoon with flow increasing from 70-90kt in
the 850-500mb layer over the northern half of the Enhanced Risk
area. It seems plausible some attempts at storm development will
occur during the afternoon near the leading edge of the mid-level
dry slot. If the stronger updrafts become sustained, they will
likely evolve into supercells with tornado potential. A corridor of
possibility for supercell tornadoes (perhaps strong) appears
greatest from the OH/MS confluence southward into northern portions
of MS on the trailing portion of large-scale ascent moving away from
the area. As storms encounter weaker buoyancy farther east and
northeast during the evening, a transition to linear structures
capable primarily of damaging winds may occur.
..Smith/Squitieri.. 03/09/2019
Mesoscale Discussion 0166
