Severe Storm Outlook Narrative (AC)
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ACUS03 KWNS 150710
SWODY3
SPC AC 150709

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0109 AM CST Fri Dec 15 2017

Valid 171200Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER MISSISSIPPI VALLEY...

...SUMMARY...
Thunderstorms will likely develop on Sunday across parts of the
central Gulf Coast region including the lower Mississippi Valley. A
few damaging wind gusts and a marginal tornado threat will be
possible.

...Lower Mississippi Valley...
A shortwave trough will move quickly northeastward into the mid
Mississippi Valley on Sunday as southwest mid-level flow remains in
place across the Gulf Coast Region. At the surface, moisture
advection will continue across the lower Mississippi Valley where
surface dewpoints are forecast to reach the lower to mid 60s F
across southeastern Louisiana and southern Mississippi by midday.
Isolated to scattered thunderstorms are forecast to be ongoing in
southwestern Louisiana at the beginning of the period with this
convection spreading eastward into the lower Mississippi Valley by
early afternoon. NAM and GFS forecast soundings at New Orleans,
Louisiana and Mobile, Alabama at 21Z Sunday afternoon show weak
instability with strong deep-layer shear. Although MLCAPE values are
only forecast to be in the 250 to 500 J/kg range, 0-6 km shear
values could be as high as 50 kt. This would be enough for a
marginal severe threat making isolated damaging wind gusts possible
with the stronger thunderstorms. 0-1 km shear of 25 to 30 kt will
also make storm rotation possible and a marginal tornado threat can
not be ruled out. As moisture advection continues and the shear
environment is maintained during the evening and overnight period, a
marginal severe threat could persist across the region.

..Broyles.. 12/15/2017

$$



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