SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CST Tue Dec 29 2020

Valid 301200Z - 311200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE TEXAS COASTAL PLAIN AND VICINITY...

...SUMMARY...
Thunderstorms -- and limited severe potential -- will affect
portions of the Texas Coastal Plain and Hill Country from late
afternoon Wednesday into the overnight hours.

...Synopsis...
A highly amplified, split flow pattern will prevail across the U.S.
Wednesday.  In the northern stream, a trough initially over the
upper Midwest is forecast to move quickly east-northeastward across
the Great Lakes, reaching New England late.  Meanwhile, a second,
eastern Pacific short-wave trough will move inland over the Pacific
Northwest early, and dig southeastward toward the Great Basin
through the period.

Meanwhile in the southern stream, an upper low is forecast to move
across northern Mexico.

At the surface, a cold front will move eastward across the Great
Lakes region and into New England, and southeastward across the
Ohio/mid and lower Mississippi/Tennessee Valleys, and southern
Plains.

Meanwhile, in response to the Mexican upper low, cyclogenesis is
expected to occur during the second half of the period near the
lower/middle Texas coast, eventually becoming commingled with the
southeastward-moving cold front.

...Texas Coastal Plain and portions of the Hill Country...
Showers and embedded thunderstorms -- ongoing at the start of the
period -- are forecast to spread southeastward across the southern
Plains Wednesday, along and behind the advancing cold front. 
Meanwhile, pre-frontal shower activity is forecast to increase ahead
of the front, with scattered thunderstorms evolving from within this
activity by evening as warm advection increases ahead of the
advancing upper system.

Limited CAPE is expected in the vicinity of the front as it advances
across Texas, with warm mid-level air/modest lapse rates limiting
convective intensity.  Still, given ample flow aloft that may aid in
sustenance of a few stronger updrafts, a 5% risk for hail appears
warranted.

Later, as a surface low develops near the southeast Texas coast, an
increase in convection just ahead of the advancing front is
expected.  With favorable low-level veering/shear, beneath amply
strong mid-level flow, a few rotating storms may evolve overnight. 
As such, very limited potential for a tornado (2%) and locally
gusty/damaging winds (5%) will be included in this outlook, centered
over the middle Texas Coastal Plain.

..Goss.. 12/29/2020

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