Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 211701
SWODY2
SPC AC 211700

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1200 PM CDT Sat Oct 21 2017

Valid 221200Z - 231200Z

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

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

...Central Gulf Coast...
An amplified mid/upper trough will advance across the central US
Sunday, with an embedded closed low evolving across the mid
Mississippi Valley Sunday night. An impulse, currently dropping
southeast along the backside of the large-scale trough, will reach
east Texas by Sunday afternoon, resulting in some modest
amplification of the trough. Meanwhile, ahead of a cold front, a
broken line of overnight convection will be pushing
east/southeastward from east Texas to the lower Mississippi Valley
through the day.

Initially, this line of storms will likely outpace stronger flow
aloft to the west, while encountering decreasing instability with
eastward extent during the morning hours. However, warm/moist
advection ahead of the trough will continue to bring a plume of rich
moisture northward (characterized by PW values around 1.75-2
inches). Forecast soundings indicate mid-level lapse rates, while
not particularly favorable for robust convection, will steepen to
around 6.5-7 C/km across portions of the central Gulf Coast. And
despite relatively weak low-level flow, southeasterly surface winds
veering with height to 50kt upper-level southwesterlies may be
sufficient for occasional updraft organization in stronger cores.
Most convection-allowing guidance and related ensemble data
highlight this area for some modest enhancement of thunderstorm
organization during the second half of the day, as cells gradually
deepen within this low-level warm advection regime. In turn,
marginal probabilities have been introduced to account for the
potential of a few stronger gusts, an isolated marginally severe
hail report, and perhaps a brief tornado during the
afternoon/evening hours.

..Picca.. 10/21/2017

$$



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