Severe Storm Outlook Narrative (AC)
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675
ACUS02 KWNS 180557
SWODY2
SPC AC 180556

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1156 PM CST Sun Dec 17 2017

Valid 191200Z - 201200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDDLE TO UPPER TEXAS COAST...EAST TEXAS...NORTH-CENTRAL
LOUISIANA INTO WEST-CENTRAL MISSISSIPPI...

...SUMMARY...
Scattered thunderstorms are expected to develop from the middle and
upper Texas Coast Plains on Tuesday afternoon moving across east
Texas Tuesday evening into north-central Louisiana and west-central
Mississippi during the overnight period. A few strong wind gusts and
a marginal tornado threat will be possible.

...Middle to Upper Texas Coastal Plains/East Texas/North-central
Louisiana/West-central Mississippi...
An upper-level trough will move from northern Mexico into southern
and central Texas on Tuesday. Ahead of the system, a moist airmass
will advect northward onto the Texas Coastal Plains. Surface heating
will take place ahead of the upper-level trough as a 30 to 40 kt
low-level jet develops during the day. This should be favorable for
scattered thunderstorms between San Antonio and Houston Tuesday
afternoon. Forecast soundings in this area at 21Z/Tuesday show
MLCAPE values around 500 J/kg with 0-6 km shear in the 50 to 60 kt
range. 0-1 km shear is forecast to be around 30 kt. This environment
should support storm rotation within cells that remain discrete. A
marginal tornado threat or potential for strong wind gusts should
exist with the stronger rotating cells.

Model forecasts move this area of scattered thunderstorms
northeastward across east Texas Tuesday evening and into
north-central Louisiana during the overnight period. By late in the
period, the storms should move into west-central Mississippi. The
environment along this corridor will continue to have weak
instability and strong deep-layer shear favorable for a marginal
severe threat. Although 0-1 km shear will increase some as a
low-level jet strengthens across the region, instability will remain
weak. For this reason, the severe threat should remain marginal with
a potential for isolated strong wind gusts and perhaps a low-end
chance for a tornado.

..Broyles.. 12/18/2017

$$



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