Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 260602
SWODY1
SPC AC 260600

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Sun Mar 26 2017

Valid 261200Z - 271200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR MUCH OF
CENTRAL OKLAHOMA INTO NORTH-CENTRAL TEXAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTH-CENTRAL
TEXAS INTO MUCH OF OKLAHOMA AND WESTERN ARKANSAS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SOUTH-CENTRAL U.S. SLIGHT RISK...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
UPPER OHIO VALLEY...

...SUMMARY...
Severe thunderstorms capable of large to very large hail, damaging
winds, and a couple tornadoes will be possible across parts of the
southern Great Plains today.  A few strong wind gusts may occur over
the upper Ohio Valley as well.

...Synopsis...
Water-vapor imagery late Saturday night shows a vigorous
lower-amplitude shortwave trough across the Four Corners and this
feature is forecast to move into the central-southern Great Plains
during the afternoon before moving into the Ozarks by daybreak
Monday.  Another mid-level trough over the OH Valley is forecast to
deamplify across this region during the day as it moves into the
lower Great Lakes.  In the low levels, a warm front over the
northwest Gulf Coast will advance northward through much of OK as a
surface low consolidates and develops east from the High Plains into
west-central OK by early evening.  An attendant dryline will aid in
focusing thunderstorm development with severe weather expected
across portions of the southern Great Plains this afternoon and
evening.

...southern Great Plains into the Ozarks...
Late Saturday night surface analysis shows a relatively dry airmass
across much of central and north-central TX to the northwest of
richer low-level moisture along the TX coastal plain.  Strengthening
southerly low-level flow will advect moisture northward during the
day beneath a capping inversion.  Strong heating to the east of a
dryline will contribute to 1000-2000 J/kg MLCAPE across a narrow
warm sector near the north-central TX/OK I-35 corridor.  As a 60-kt
500 mb speed max noses into OK and north-central TX during the
afternoon, increasing ascent and weakening convective inhibition
will likely result in a band of storms developing and moving to the
east of the dryline.  A discrete cellular mode will be preferred
early and effective shear around 50-kt and moderate buoyancy will
strongly favor supercell development with the stronger updrafts.
Cold 500-mb temperatures (-16 degrees C) and large CAPE in the -10
to -30 degree C layer will likely promote efficient hail growth with
any supercells that form---resulting in large to very large hail.
If short-term models continue to show strong agreement in supercell
development from I-40 in central OK to just south of the Red River,
a higher hail probability may be introduced in a later outlook.
Questions concerning the tornado risk are dependent on the quality
of low-level moisture as a 40-kt southerly LLJ will be maintained
through early evening.  Enlarging of hodographs towards 00z will
likely maximize low-level mesocyclone potential and it appears a
couple of tornadoes are possible.  The LLJ will veer to
southwesterly during the overnight over the ArkLaTex and Ozarks and
a hail/wind risk will probably spread east into eastern OK/northeast
TX and the Ozarks.

...upper OH Valley...
The aforementioned weakening mid-level trough will pivot across this
area during peak heating.  Scattered showers and thunderstorms will
probably develop coincident with weak buoyancy.  Forecast soundings
show relatively saturated profiles which would tend to limit hail
growth.  A few of the stronger multicells that develop may pose a
risk for isolated damaging winds during the afternoon.

..Smith/Marsh.. 03/26/2017

$$



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