Severe Storm Outlook Narrative (AC)
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683
ACUS01 KWNS 280609
SWODY1
SPC AC 280608

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0108 AM CDT Tue Mar 28 2017

Valid 281200Z - 291200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL AND SOUTHERN OKLAHOMA ACROSS NORTH TEXAS INTO THE CONCHO
VALLEY AREA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS INCLUDING LARGE
PORTIONS OF OKLAHOMA AND TEXAS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHERN PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
VIRGINIA AND NORTH CAROLINA...AND VICINITY...

...SUMMARY...
Scattered to numerous severe storms are forecast Tuesday and Tuesday
night across the southern Plains.  A few strong to severe storms are
also possible over parts of the Mid-Atlantic region.

...Synopsis...
A large mid- and upper-level trough/low initially centered over the
Four Corners states will move eastward across the southern Rockies
during the day, gradually emerging into western portions of the
southern Plains through the afternoon and evening.  Meanwhile, a
much weaker short-wave trough crossing the central Appalachians and
vicinity early in the period will shift toward/off the middle and
southern Atlantic coasts through the daytime hours.

At the surface, a weak low will cross the Virginia/North Carolina
vicinity through the day.  Over the southern Plains, a low is
forecast to move out of eastern New Mexico into/across the high
Plains of Texas through the afternoon and evening.  A dryline will
mix very slowly eastward across west Texas through the day -- and
should be overtaken by a faster-moving Pacific cold front during the
evening/overnight.  Meanwhile, a west-to-east warm front is forecast
to be lifting gradually northward across Texas through the day,
likely shifting northward into Oklahoma during the evening/overnight
as low-level flow strengthens.  This surface system and the
associated upper low/trough will support widespread convection and
enhanced severe weather risk across much of Texas and northward into
Oklahoma -- particularly during the late afternoon and evening
hours.

...The southern Plains...
Persistent southerly low-level flow ahead of the advancing storm
system will allow moistening of the boundary layer through the day,
along with gradual northward shift of the west-to-east warm front
across Texas with time.  As a dryline mixes slowly eastward across
the South Plains and Transpecos region, initiation of storms is
forecast by mid to late afternoon -- both along the dryline and
perhaps, in a more isolated manner, northwestward into portions of
the Texas Panhandle.

As the storms initiate within a moderately unstable environment,
strengthening flow aloft -- veering from southeasterly at the
surface to south-southwesterly aloft -- updrafts will acquire
rotation and become capable of producing very large hail and locally
damaging gusts.  Additionally, initial cellular mode suggests
potential for a few tornadoes -- particularly across western North
Texas where a strong tornado will be possible.

As storms mature, upscale growth into lines (with bowing segments)
is expected -- due to both very strong large-scale ascent and
meridional flow aloft roughly parallel to the dryline/developing
cells.  The band of storms should accelerate across north Texas and
into southern/central Oklahoma during the evening, along with
attendant risks for damaging winds and hail, and possibly an
additional tornado or two.

Meanwhile, additional storm development is expected during the
evening farther southwest along the advancing Pacific front.  As
this front merges with the dryline, the band of storms may elongate
both northward and southward, with northern portions of the band
possibly bringing a second round of storms/possible severe weather
to parts of Oklahoma and north Texas.  Farther south, the convection
should advance east across much of central Texas through the evening
and overnight along with risk for hail and locally damaging winds.

...The Virginia/North Carolina vicinity...
Multiple rounds of showers and isolated thunderstorms are forecast
to move across the VA/NC vicinity during the first half of the
period, as the upper system moves across the area.  Due to
clouds/ongoing precipitation as ascent spreads eastward across the
area relatively early in the diurnal cycle, destabilization is
likely to remain somewhat subdued.  This -- in conjunction with the
relative weakness of the system -- suggests overall severe risk
should remain tempered.  As such, will maintain only MRGL risk for
wind/hail with isolated stronger cells at this time.  Risk should
diminish through late afternoon, and end by evening as the system
moves offshore.

..Goss/Cohen.. 03/28/2017

$$



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