Day 1 Severe Weather Outlook

Valid 091630Z – 101200Z


Severe thunderstorms, with a primary threat of large hail, are
possible beginning this evening in north Texas and continuing
through tonight into southern Arkansas and northern Louisiana.

…North TX this evening to AR/LA overnight…
A northern stream shortwave trough will move from the upper Midwest
to the Great Lakes, while in its wake a surface cold front moves
southward across the southern Plains. South of the cold front, an
increasingly moist air mass is spreading inland from the western
Gulf of Mexico into TX, where boundary-layer dewpoints have
increased to the mid 60s in central TX and the upper 60s across
south TX. This moistening is occurring beneath an elevated mixed
layer that has (thus far) acted to cap the moist layer. Through
most of the day, a few showers are expected in the deepening moist
layer below the cap across TX. Clouds will slow surface heating and
help maintain the cap through much of the warm sector today, though
there is an area of stronger surface heating/mixing across north TX,
along the west edge of the richer low-level moisture. Reduction of
the cap through surface heating/mixing across western north TX, and
continued moistening and warm advection near the northeast edge of
the warmer elevated mixed layer into northeast TX/southeast OK,
should support thunderstorm development this evening into tonight.

The background environment with dewpoints in the 60s beneath 7.5-8
C/km midlevel lapse rates will support moderate buoyancy (MUCAPE of
1500-2000 J/kg). Vertical shear will be sufficient for supercells
in the warm sector, though low-level shear will tend to weaken
slowly into tonight, as the primary low-level jet develops
northeastward and away from the warm sector. Thus, a mix of
cells/clusters with some supercell structures will pose a threat for
large hail and isolated damaging gusts, though an isolated tornado
or two cannot be ruled out this evening. The marginal hail threat
with elevated storms may extend eastward across northern LA and
southern AR overnight with MUCAPE near 1000 J/kg and midlevel lapse
rates in excess of 7 C/km.

…Edwards Plateau near 12z…
Near the end of the period, a strong storm or two may form in the
area a little north-northwest of Del Rio, along the cold front and
in advance of an ejecting southern stream trough that is now west of
Baja. While isolated large hail cannot be ruled out, the threat is
uncertain and confined to the very end of the period (or possibly
early day 2), so no probabilities will be added in this update.

..Thompson/Squitieri.. 02/09/2020


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