Severe Storm Outlook Narrative (AC)
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000
ACUS01 KWNS 211913
SWODY1
SPC AC 211912

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0112 PM CST Wed Feb 21 2018

Valid 212000Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
LOUISIANA INTO WESTERN MISSISSIPPI...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE SABINE
RIVER INTO CENTRAL MISSISSIPPI...

...SUMMARY...
Thunderstorms will continue from Texas today to the Ohio Valley and
Appalachians today into tonight, some of which will be associated
with freezing or frozen precipitation across northwest Texas and
Oklahoma.  A couple of tornadoes and isolated strong wind gusts will
be possible with the storms across Louisiana and adjacent areas of
southeast Texas and west central Mississippi.

...Louisiana into western Mississippi...
A primary cluster of storms continues to evolve over central LA,
moving slowly northeastward ahead of a slow-moving front. Trends
indicate these storms have evolved into a small MCS, with embedded
supercells. A tornado or two along with wind damage remains
possible, and the presence of warming air downstream may enhanced
the potential for a few hours. The area immediately ahead of or
along the front may be a preferred corridor. However, this front
will also demarcate the northern extent of the threat area. While
other isolated cells may form farther south of the main cluster,
low-level shear is not quite as strong, with a relatively lesser
threat. For more information see mesoscale discussion 81.

..Jewell.. 02/21/2018

.PREV DISCUSSION... /ISSUED 1004 AM CST Wed Feb 21 2018/

...Lower MS Valley and southern Plains through tonight...
A deep warm/moist conveyor belt is established from the western Gulf
of Mexico into the lower MS Valley, along and immediately southeast
of a slow-moving cold front.  The pattern will change little through
tonight as the large-scale ridge persists over the southwest
Atlantic and at least two shortwave troughs continue to dig
southward/southeastward along the Pacific coast to maintain the mean
western trough.  Within the warm conveyor belt, a maritime tropical
air mass (boundary layer dewpoints near 70 F) will continue to
spread northward across LA/MS today, with some surface heating
possible along the southeast periphery of the ongoing warm sector
convection.  The storms are likely to persist through the day in
this moist and uncapped environment per regional 12z soundings,
where deep-layer vertical shear will be sufficient for supercells
within the larger storm clusters.  Given the rich low-level moisture
and effective SRH in excess of 200 m2/s2, a couple of tornadoes will
be possible, along with isolated strong wind gusts.

Otherwise, a swath of elevated convection will continue above the
shallow cold air mass across the southern Plains.  The boundary
layer will be sufficiently cold for a mix of sleet and freezing rain
with the elevated convection from northwest TX into southern OK
today through early tonight.

$$



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