Day 1 Severe Weather Outlook

Valid 171300Z – 181200Z

…NO SEVERE THUNDERSTORM AREAS FORECAST…

…SUMMARY…
Thunderstorms are expected from southern and central Texas to the
southern Ozarks today into tonight. No severe weather is
anticipated.

…Synopsis…
A progressive upper-air pattern will feature a well-defined
synoptic-scale trough, now negatively tilted from coastal BC and the
Pacific Northwest across the Great Basin and northern AZ. This
trough will move eastward through the period, phasing with an
initially weak shortwave over the central High Plains to form a
closed 500-mb low over northern MN by 12Z. At that time, the trough
should arc from the low across northeastern IA, north-central MO and
northeastern OK. The southern extension of the leading shortwave
trough is apparent in moisture-channel imagery across eastern NM to
southern Baja. This feature will move eastward across western OK
and west/northwest TX today, weakening and accelerating eastward
across much of the Ohio and Tennessee Valleys overnight.

At the surface, 11Z analysis showed a wavy cold front from Atlantic
waters northeast of the Bahamas, across south FL, west-northwestward
over the north-central/northwestern Gulf, becoming quasistationary
over the middle TX coastal plain near VCT, southwestward across
eastern Nuevo Leon. The western part of the frontal zone over TX
will become diffuse amidst a strengthening low-level warm-advection
regime related to cyclogenesis now occurring over the southeastern
MT/northeastern WY region. That low should deepen and move across
the upper Mississippi Valley around 12Z, with cold front reaching
northwestern IL, south-central MO, southeastern OK, and central/
southwest TX.

…Southern Plains…
Isolated to widely scattered, episodic thunderstorms are forecast
across the outlook area through the period. While a few
thunderstorms may occur outside these regimes, the primary
contributors to total thunderstorm coverage of at least 10% should
be:
1. A corridor of deep ascent currently extending from northwest TX
south-southwestward across west-central TX into northwestern
Coahuila. This appears to represent a combination of modest DCVA
preceding the leading shortwave trough with the western rim of
low-level warm advection. This convection should shift
northeastward and mostly weaken through the early evening. However,
associated thunder potential in the UVV plume may cycle back up
again tonight ahead of the cold front, in the tail section of an
increasingly moist, 40-60-kt LLJ developing in response to
north-central Plains cyclogenesis.
2. In the last few hours of the period (pre-dawn hours tomorrow),
the low-level cold front will encounter the same moistened sector
and may initiate a narrow band of convection with embedded
thunderstorms.

In both regimes, the bulk of supportive buoyancy will be elevated
and decreasing poleward, modulated by modest lapse rates and low
CAPE density in the deep convective layer. Effective-shear
magnitudes mostly should remain around 35 kt or less. As such,
severe potential appears too low for unconditional probabilities.

..Edwards/Gleason.. 01/17/2020

$$

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