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Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1236 PM CDT Tue Apr 07 2020

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE
MID MS VALLEY AND OVER PORTIONS OF CENTRAL TX...

...SUMMARY...
Scattered strong to severe thunderstorms are possible over parts of
central Texas Wednesday afternoon and the Middle Mississippi Valley
on Wednesday evening and overnight. Large hail, damaging gusts, and
perhaps a couple of tornadoes are the primary hazard.

...Synopsis...
A split-flow pattern is forecast to be in place across the CONUS
early Wednesday morning. Primary features within this pattern will
be a northern-stream shortwave trough, which is expected to progress
southeastward through the northern Plain and Mid/Upper MS Valley,
and a southern-stream closed low, which is expected to slowly drift
eastward over southern CA. More pertinent to the severe weather
threat, a low-amplitude shortwave trough is expected to progress
through the southern-stream over the southern Plains and Lower MS
Valley. Confluence of the two streams will occur over the MS River
Valley, with relatively strong flow aloft persisting, and then
increasing late in the period, over the eastern CONUS.

Primary feature within the surface pattern will be a cold front that
is expected to surge southeastward from the northern Plains/upper MS
Valley into the central Plains/mid MS Valley by Wednesday evening,
continuing eastward/southeastward through the southern Plains,
Mid-South, and TN/OH Valleys by Thursday morning. Moist
southwesterly low-level flow will advect high theta-e air into the
mid MS Valley ahead of this front while maintaining the moist air
mass already in place from east TX through the Southeast.

...Mid MS Valley into portions of the OH/TN Valleys...
A somewhat broad area of Slight-risk equivalent severe weather
probabilities will exist over much of the region Wednesday. This is
due to different model depictions of low-level moisture return, cap
strength, and frontal timing as well as at least some modest risk
for pre-frontal development. The general expectation is for
thunderstorms to initialize along the front during the afternoon and
then push southeastward throughout the evening. Initial storm mode
will likely be cellular, with the thermodynamic and kinematic
profiles supporting the threat for very large hail. Given the linear
forcing, a quick linear transition is anticipated, with the severe
threat also transitioning from hail to damaging wind gusts. Tornado
threat will be non-zero, but relatively weak and veered low-level
flow suggests low potential for development.

The overall threat appears highest across northeast MO and adjacent
western IL southeastward into southern IL and southeast MO although
not high enough to delineate higher probabilities with this outlook.
An upgrade may be needed in subsequent outlooks if a corridor of
higher risk appears more likely. A more conditional severe threat
exists south in AR, where frontal timing will be less favorable but
more moist low-level conditions will exist. Any storm within this
environment would likely be severe.

...TX Hill Country/Central TX...
Low-amplitude, southern-stream shortwave trough mentioned in the
synopsis will likely provide enough ascent to foster thunderstorm
initiation over the region during the afternoon. Thermodynamic
environment will be characterized by ample low-level moisture (i.e.
dewpoints in the upper 60s/low 70s) beneath steep mid-level lapse
rates. Resulting strong buoyancy coupled with deep-layer shear
around 40-50 kt should be more than supportive for organized storm
structures. Initial threat will be large hail, with some instances
of very large hail possible. The initially cellular mode will likely
transition more linear quickly, with the primary threat then
transitioning to damaging downburst winds resulting from
water-loaded downdrafts. An initial supercell mode will also result
in a low-probability threat for an isolated tornado, although
low-level winds do not appear overly favorable for low-level
rotation.

...Southeast into the Mid-Atlantic...
Residual boundaries from antecedent showers and thunderstorms will
likely act as an impetus for additional convective initiation
Wednesday afternoon. Relatively deep and strong northwesterly flow
aloft would likely support organized storm structures and an
attendant severe weather threat. Mesoscale nature of this threat
precludes any corridors of higher potential on this outlook, but
updgrades may be needed in following outlooks once mesoscale
features become more predictable.

#Thunderstorm
#Tornado
#NWS

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