Day 1 Severe Weather Outlook

Valid 151300Z – 161200Z


Severe thunderstorms are possible mainly across parts of west Texas.

A blocky mid/upper-level pattern will remain in place over the
northeastern Pacific, as a high-amplitude ridge resides northwest
through southwest of a strong synoptic cyclone moving slowly
southward off the coastline of northern CA. In the broad field of
southwest flow located southeast of that cyclone, a southern-stream
perturbation was evident in moisture-channel imagery from northern/
central Baja southward over the Pacific west of southern Baja. Part
of the feature should move to the Big Bend/Trans-Pecos region by
around 00Z.

At the surface, 11Z analysis showed a cold front from the southern
Appalachians across northern portions of MS/LA, becoming slow-moving
to stationary from east to south-central TX, across extreme northern
Coahuila to a weak low over the Big Bend area of TX. The frontal
zone effectively should back northwestward today amidst a
combination of low-level theta-e advection and diurnal heating,
especially over and adjacent to the ranges between the Big Bend area
and I-10.

…West TX…
Isolated to scattered thunderstorms are expected to develop on
either side of the surface front, with the most probable area for
surface-based storms in the outlook being roughly southwest of the
Pecos River. On the poleward side of the front, convection is
possible throughout the period, with episodic hail being the main
concern. In the warm sector, thunderstorms should form over higher
terrain on either side of the Rio Grande and move eastward to
northeastward, in an environment at least temporarily favoring
supercells. Forecast soundings suggest favorably high theta-e in
the Big Bend/Davis Mountains region, with strong heating especially
near the Rio Grande, underlying steep midlevel lapse rates.

With surface dew points commonly in the 60s F extending west of the
Pecos River on easterly/upslope flow component, preconvective MLCAPE
1500-2000 J/kg appears probable. The easterlies will continue to
transport moisture into the area ahead of convection and contribute
to a combination of favorable deep shear and storm-relative low-
level winds. Effective-shear magnitudes 55-70 kt are possible,
albeit with some weaknesses in low/middle-level flow that can
contribute to messy storm modes with time. The window for discrete-
supercell potential may be rather limited, as convective coverage
potentially increases substantially in just a few hours after
initiation. Still, as long as any supercells are occurring, severe
hail and damaging wind are possible, and a tornado cannot be ruled
out. Some upscale growth into a short-lived/wind-dominant cluster
or MCS may occur this evening until activity moves over
progressively more-stable low-level conditions.

..Edwards/Goss.. 03/15/2020


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