Day 1 Severe Weather Outlook

Valid 131300Z – 141200Z


Severe hail, isolated damaging wind and the potential for a couple
tornadoes are expected this afternoon into early evening, from
southeastern New Mexico over parts of west Texas.

A strong mid/upper-level shortwave trough is apparent in moisture-
channel imagery extending southwestward from coastal BC. This
perturbation will dig southeastward and evolve into a strong, closed
cyclone covering much of the Pacific Northwest and adjacent ocean
waters by the end of the period. As this occurs, a formerly cut-off
cyclone — currently over southern CA and northern Baja — will
devolve rapidly into an open-wave, positively tilted trough. By
00Z, the trough should reach the CO/UT border area and central/
eastern AZ. By 12Z, a still-weaker version of the trough should
extend near an axis from HON-ONL-GCK-HOB.

The 11Z surface analyses showed a cold front across portions of
southwestern PA, WV, southern middle TN, and northern parts of MS,
becoming quasistationary over northern LA and north-central/
northeast TX. The front has become diffused farther west by a
shallow current of outflow from overnight thunderstorms that has
settled southward across parts of the Edwards Plateau and Big Bend
regions. Warm and moist advection should contribute to
repositioning the effective baroclinic zone northward through
early-mid afternoon near its pre-outflow position across west-
central TX and the Permian Basin. The TX frontal segment then
should remain near its present position through the rest of the
period, with mesoscale oscillations in response to both the
weakening/ejecting trough, and convective perturbations of the

…Southeastern NM, west TX…
Widely scattered to scattered thunderstorms are expected to form
this afternoon over eastern slopes of higher terrain rimming the
western parts of the outlook area, from southeastern NM through the
Davis Mountains and perhaps into the Big Bend area. This activity
should develop on both sides of the surface baroclinic zone, aided
by a combination of weak upslope-flow component and heating of
higher terrain, leading to preferential/earlier removal of MLCINH in
the western part of the outlook.

Large hail will be the main concern poleward of the front, the
threat decreasing northward in step with weaker elevated buoyancy/
lapse rates. Significant/2 inch hail may occur, conditional on
sustained supercell structure, but too much uncertainty exists on
coverage and location for a 10% risk area at this time. Damaging
gusts are possible both near the higher terrain and across parts of
the warm sector along and south of the front, before nocturnal
diabatic cooling and associated near-surface stabilization restrict
the eastward extent of the threat this evening. Tornadoes may occur
from any mature, surface-based supercells, especially in areas of
backed surface flow near the front where hodographs will be the most
curved and elongated, maximizing SRH in the lowest km.

Warm-sector surface dew points in the mid 50s to low 60s F, along
with gradual diurnal heating tempered by cloud cover, will support
MLCAPE in the 1000-2000 J/kg across west TX. Similar values are
possible in a narrow, north-south corridor in southeastern NM where
somewhat less boundary-layer moisture will be available, but
beneath colder midlevel temperatures. Strong directional shear and
mid/upper-level southwesterlies will contribute to effective-shear
magnitudes in the 55-70-kt range.

..Edwards/Goss.. 03/13/2020


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