Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 220545
SWODY1
SPC AC 220544

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1244 AM CDT Sun Oct 22 2017

Valid 221200Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL GULF COAST REGION...

...SUMMARY...
A couple of marginally severe storms will be possible Sunday
afternoon and evening near the central Gulf Coast.

...Synopsis...
Upper ridging is forecast to prevail over the eastern U.S. through
the period, though will be gradually shunted east by the steady
advance of central U.S. troughing.  Meanwhile, flat/zonal flow
initially expected over the West will gradually turn anticyclonic,
as ridging amplifies upstream of the central U.S. trough.

At the surface, a cold front is forecast to advance eastward across
the Mississippi Valley during the day, and then continue across the
Ohio and Tennessee Valleys/Central Gulf Coast states through the
remainder of the period.

...Central Gulf Coast region...
Showers and thunderstorms are forecast to be ongoing early in the
period near and ahead of the advancing surface cold front, west of
the lower Mississippi Valley area, while more isolated/pre-frontal
convection is expected over portions of the MRGL risk area.

While generally weak lapse rates aloft will prevail across the
region, a very moist low-level airmass will combine with some
heating to support modest diurnal destabilization.  As the front
crosses the lower Mississippi Valley through the late morning and
early afternoon hours, the gradual increase in CAPE over the area
should support an uptick in convective coverage and intensity.

With weakly veering/increasing flow with height expected atop the
region -- particularly as the front advances, a few severe storms
may emerge from amidst the broader area of convective activity.
Risk for a locally stronger/damaging gust or two may evolve during
the afternoon, and possibly some marginal hail and even a tornado
with one or two of the strongest cells.  At this time however, it
still appears that the weak lapse rates/limited CAPE expected should
hinder overall degree and coverage of severe risk, warranting
maintenance of MRGL risk level at this time.

..Goss.. 10/22/2017

$$


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