Day 1 Severe Weather Outlook

Valid 041200Z – 051200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF SOUTHEAST TEXAS AND FROM NORTHEAST TEXAS INTO THE TENNESSEE
VALLEY…

…SUMMARY…
A marginal risk for isolated severe thunderstorms is forecast today
into tonight from east Texas into the Mid-South. A few strong wind
gusts are the main threat, but some hail will also be possible over
a portion of southeast Texas late tonight.

…Northeast Texas into the Tennessee Valley region…

The shortwave trough now accelerating through the southern Plains
will continue northeast through the lower MS Valley early in the
period. In wake of this feature a positive-tilt upper trough will
move slowly east through the southwest U.S., reaching the southern
High Plains later tonight. The forcing for ascent associated with
the upper trough will lag behind the surface front that should
extend from the OH Valley through northwest AR and northwest TX at
12Z today. The front will advance southeast and stretch from the TN
Valley southwest through LA to along the TX coast by the end of this
period. Showers and a few thunderstorms will likely be ongoing early
today along the warm conveyor belt and in vicinity of the front from
AR into TN and KY. In wake of the early activity some
destabilization is expected in the warm sector from east TX to the
lower MS and TN Valley owing primarily to modest theta-e advection
with dewpoints increasing to mid 60s F as far north as southern AR
by early evening. However, widespread clouds and weak mid-level
lapse rates should limit MLCAPE to near or below 600 J/kg. Forecast
soundings show a modest capping inversion around 750 mb, especially
with southwest extent into TX.

Deep layer forcing will remain weak in wake of lead shortwave
trough, but additional storms may develop mainly from AR and
northern MS into the TN Valley this afternoon and tonight along the
southeast-advancing cold front. The low-level jet is forecast to
weaken during the day, but effective bulk shear from 40-50 kt will
persist within the broad fetch of stronger southwest winds aloft. A
few of the storms may organize and pose a risk for mainly isolated
damaging wind gusts and perhaps a brief tornado. The marginal
thermodynamic environment and lack of phasing between the warm
sector and deeper forcing accompanying the upper trough is expected
to serve as limiting factors for a more robust severe event.

…Southeast Texas…

A dryline will mix east through central TX today prior to cold front
arrival. The moist warm sector ahead of this feature will become
marginally unstable and is expected to remain capped to any
surface-based development. Later tonight an upper jet rotating
through the base of the upper trough will spread into south TX with
an attendant increase in the low-level jet. This process will
increase theta-e advection and isentropic ascent in post-frontal
zone resulting in elevated instability (400-800 J/kg MUCAPE) and the
development of a few thunderstorms. Strong effective shear though
the cloud layer along with up to 7 C/km mid level lapse rates might
support a risk for a few instances of marginally severe hail with
the stronger storms.

..Dial/Bentley.. 02/04/2020

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