SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1126 AM CST Fri Dec 18 2020

Valid 191200Z - 201200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDDLE/UPPER TEXAS COAST...

...SUMMARY...
Isolated strong to severe thunderstorms may occur Saturday across
parts of the middle/upper Texas Coast.

...Middle/Upper Texas Coast...
A shortwave trough over the southern/central Plains Saturday morning
is forecast to move eastward to the lower/mid MS Valley by Saturday
evening. At the surface, a cold front will likely extend
southwestward across central TX from a weak low near southeastern OK
and northeastern TX at the start of the period. Generally elevated
thunderstorms may be ongoing Saturday morning across parts of
central/east TX in a modest low-level warm/moist advection regime.
Weak MUCAPE (less than 500 J/kg) should preclude a severe risk
along/north of the cold front through much of the morning.

Ahead of the cold front, low to perhaps mid 60s surface dewpoints
should advance northward into parts of the middle/upper TX Coast
region by midday. Even though diurnal heating will likely be muted
by widespread cloud cover and mid-level lapse rates should remain
poor, there is some potential for MLCAPE around 250-500 J/kg to
develop by early Saturday afternoon ahead of the front along/near
the coast. Assuming sufficient boundary-layer destabilization, there
will be enough deep-layer shear (40-50 kt) to support updraft
organization. Isolated strong/gusty winds should be the main threat
with any robust storms that can develop over land, before they move
offshore fairly quickly early Saturday afternoon. Even though
low-level flow is not forecast to be overly strong, around 100-150
m2/s of 0-1 km SRH may be present very near the coast. Accordingly,
a brief tornado cannot be ruled out.

Once storms move over the Gulf Saturday afternoon, the marginal
severe threat across parts of the middle/upper TX Coast will end. A
weak surface low may develop eastward along/near the LA Coast
Saturday evening and overnight as the mid-level shortwave trough
continues moving eastward. However, the inland advance of
substantial low-level moisture appears unlikely, with generally
elevated convection expected across LA and the lower MS Valley
Saturday night.

..Gleason.. 12/18/2020

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