Day 1 Severe Weather Outlook

Valid 031300Z – 041200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
SOUTHWEST TO CENTRAL TEXAS…

…SUMMARY…
Thunderstorms may produce strong to isolated severe gusts late this
afternoon into evening, over portions of southwest to central Texas.

…Synopsis…
The upper-air pattern will be dominated by an expansive area of
cyclonic flow over the western CONUS, anchored by a cyclone now
apparent in moisture-channel imagery over the southern ID/
northeastern NV region. The associated vorticity lobe is forecast
to move east-southeastward to southeastward and elongate, while a
trailing vorticity banner develops over coastal central/southern CA
amidst sharpening cyclonic curvature and strengthening horizontal
shear. The net effect should be amplification of the overall
synoptic trough, despite the devolution of the cyclone into an open
wave.

By 12Z tomorrow, the synoptic trough should extend from eastern WY
across northern AZ and northern Baja, with a large field of height
falls from the central/southern Rockies and High Plains across the
Southwest and northwestern MX. In response to these developments,
an initially potent southern-stream shortwave trough — now over
southern Baja with a weak embedded cyclone — will eject
northeastward and weaken. Still, a convectively influential
perturbation should cross north-central MX today and reach south TX
this evening.

At the surface, 11Z analysis showed a low over west-central KS near
GBD, with cold front southwestward across extreme southeastern
through central CO. A warm front was drawn from the low eastward
near a COU-LEX line, with a quasistationary front from the low
northeastward near IRK-MKE. The frontal zones east of the low
should merge from west-east through the period as the low migrates
along the southern boundary toward IND. West of the low, the cold
front should move to southeastern KS, southwestern OK and
northeastern NM by 00Z. By the end of the period, the cold front
should reach southern MO, northwest TX and east-central/central NM.

…Southwest/central TX…
Scattered high-based thunderstorms are expected to develop this
afternoon over higher terrain on either side of the Rio Grande
separating TX and Coahuila, mainly across the Big Bend/Serranias del
Burro corridor, in a regime of minimal MLCINH and increasing large-
scale lift. Much of this activity (especially in the first few
hours of the convective cycle) should form west of the substantial
Gulf moist-advection plume — in a zone of prefrontal low-level warm
advection, and increasing midlevel DCVA preceding the ejecting Baja/
northern MX shortwave trough. Thunderstorms then may expand in
coverage upon encountering the greater moisture from late afternoon
into evening hours across central TX, extending overnight into the
Ozarks region.

Within that broader regime, the modified 12Z DRT sounding, and
assorted model forecast soundings, suggest that the early/
southwestern phase of this activity initially will be rooted at
least partly in an elevated layer of marginally favorable moisture
and weak MUCAPE (generally less than 500 J/kg). However, as the
convection crosses parts of the southern Edwards Plateau/Hill
Country region, and adjoining northern rim of the Rio Grande Valley,
it may encounter a diurnally heated, well-mixed and deep boundary
layer that could encourage more development and render some updrafts
effectively surface-based for a few hours. DCAPE 700-1200 J/kg may
be present below cloud base, encouraging strong/isolated severe
gusts to reach the surface. The near-surface layer will cool and
stabilize nocturnally and with northeastern extent toward central
TX, but enough dry air may linger between that layer and LCL that
strong gusts can penetrate to the surface. The already marginal
wind potential should lessen and become more conditional with
northeastward extent across central/south-central TX this evening.

..Edwards/Kerr.. 02/03/2020

$$

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