SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0646 AM CST Wed Dec 30 2020

Valid 301300Z - 311200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH TONIGHT FOR PARTS OF SOUTH AND SOUTHEAST TX...

...SUMMARY...
Isolated large hail, damaging winds, and a tornado or two will be
possible this afternoon through tonight across parts of south and
southeast Texas.

...South TX later today into tonight...
A midlevel shortwave trough over northwestern Mexico will move
eastward over northern Mexico and evolve into a closed low south of
the Big Bend by Thursday morning, as an upstream trough digs
southeastward over the Pacific coast.  In the wake of a northern
stream shortwave trough, a surface cold front will move
southeastward across central TX today, per observed pressure rises
this morning from OK into west TX.  The movement of the front will
slow tonight in response to cyclogenesis near the middle and lower
TX coast, in the zone of ascent downstream from the northern Mexico
closed low.  This pattern will also maintain a 30-40 kt southerly
low-level jet over the TX coast, and a continued inland transport of
mid-upper 60s boundary-layer dewpoints.

A few thunderstorms are expected today along the cold front from
central into northeast TX, on the north edge of the richer low-level
moisture and at least weak buoyancy.  Gradual moistening and
weakening of a lingering midlevel cap will allow for more widespread
thunderstorm development tonight along the front/near the developing
surface low, and along a commonly observed pre-frontal confluence
zone from the northwest Gulf of Mexico into the middle TX coastal
plain.  The threat for supercells and a tornado or two will increase
near the end of the period in the confluence zone near the coast, as
deep-layer and low-level shear increase in the warm sector. 
Otherwise, a band of convection will likely form across south TX
along the surging cold front overnight, with the potential for
isolated damaging gusts and marginally severe hail.

..Thompson/Gleason.. 12/30/2020

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