SPC AC 281254
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0754 AM CDT Tue Mar 28 2017
Valid 281300Z - 291200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS NORTHWEST TX AND
FAR SOUTHWEST OK...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS CENTRAL OK TO
THE EDWARDS PLATEAU...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF OK/TX...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF
SOUTHERN GREAT PLAINS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS VA/NC...
Numerous severe storms are expected across the southern Great
Plains, mainly after 2 pm CDT into tonight. Very large hail,
tornadoes, and damaging winds will be possible.
Vigorous shortwave trough over eastern AZ will shift east and reach
the southern High Plains by early Wednesday. Surface cyclone over
the Permian Basin will move northeast into northwest TX and become
quasi-stationary. By late afternoon, a bulging dryline will sharpen
to the south of this cyclone. A Pacific cold front will overtake the
dryline in west Texas this evening and sweep east into central Texas
overnight. A warm front will advance across northern TX and should
arc from the cyclone across the Red River into eastern OK by 00Z.
...Southern Great Plains...
Rich gulf moisture characterized by mean mixing ratios to 14 g/kg
per 12Z Del Rio, Corpus Christi, and Lake Charles RAOBs has become
prevalent in the broadening warm sector over central/south TX. While
diurnal mixing may yield pockets of lower dew points over
central/east TX, a plume of lower to middle 60s surface dew points
will be sustained along the dryline and warm front. Beneath a stout
EML with very steep lapse rates to 9 degree C/km from 700-500 mb per
12Z Del Rio RAOB, moderate to large buoyancy is expected ahead of
the dryline. MLCAPE should reach 1500-3000 J/kg across the Edwards
Plateau and Big Country. The leading edge of 50-kt 500-mb
south-southwesterlies will spread east over this instability axis by
late afternoon, yielding an environment favorable for supercells.
While elevated storms will increase over the Texas Panhandle through
midday, surface-based storms should develop towards mid-afternoon
near the surface cyclone. Scattered storms will form farther south
along the dryline late afternoon, with WAA-driven storms possible
farther east over north-central TX. Initially discrete supercell
mode should favor very large hail and localized severe wind gusts.
Relatively high confidence in the coverage and location of storms
warrants an upgrade to a hail-driven moderate risk from the Big
Country into southwest OK. A few tornadic storms appear probable in
this similar corridor. However, the temporal overlap of discrete
cells with enlarging hodographs may be relatively short in the open
warm sector. Low-level hodographs will be quite enlarged along the
warm front, but should be coincident with modest low-level lapse
rates and predominant cluster to linear mode. As such, an upgrade to
15 percent tornado probabilities does not appeared warranted this
As storms mature, upscale growth into lines with embedded bowing
segments is expected due to both the strong large-scale ascent and
meridional flow aloft generally paralleling the dryline. These
linear bands should accelerate northeast into southern/central
Oklahoma during the evening, with attendant risks for damaging
winds, hail, and a couple tornadoes.
Farther south over the Edwards Plateau, initially isolated to widely
scattered late afternoon/early evening storms should become
widespread in coverage during mid-late evening as the Pacific front
merges with the dryline. This should result in a predominant risk of
large hail transitioning quickly to strong to severe wind gusts. An
extensive squall line will likely evolve east overnight with an
isolated severe risk spreading into central TX.
A dampening shortwave impulse over WV will shift off the VA/NC coast
by mid-evening. Ongoing showers and isolated storms will subdue
destabilization early in the diurnal heating cycle. However, by late
afternoon, widely scattered storms should develop ahead of the
impulse. Increased veering of the wind profile with height should
foster mainly discrete cells, some of which should weakly rotate.
Isolated severe hail and damaging wind appear possible.
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