SPC AC 201617
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1017 AM CST Tue Feb 20 2018
Valid 201630Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
TEXAS INTO THE OZARKS...
Thunderstorms are expected across a broad part of the south-central
U.S. into the Midwest, with the possibility of a few strong to
locally severe storms through this evening from central Texas into
parts of the Ozarks.
A broad long wave trough is expected to persist over the western
CONUS as an initial short wave trough near the four-corners areas
lifts northeastward and deamplifies, and an upstream short wave
trough off the Pacific NW coast moves southward toward the central
California coast. A strong cold front at the surface, currently
located from extreme northwest Illinois into southwest Missouri,
southwest Oklahoma into east central New Mexico, will continue
moving southeastward into across the middle Mississippi Valley and
the southern Plains.
...Southern Plains into the Ozarks...
Multiple bands of convection are occurring within a broad region of
moist southwest flow aloft from central Texas into the Midwest. 12Z
regional soundings ahead of the cold front indicate generally weak
deep layer lapse rates but FWD and OUN soundings exhibited layers of
7-8 C/km lapse rates that are enhancing zones of buoyancy.
Thunderstorms have organized into several lines over north central
Texas with radar depicting occasional bow echo signatures moving
toward the northeast. Latest VAD wind profiles show winds of 40-50
kt in the lowest 1 km AGL suggesting potential for a few strong to
locally severe wind gusts to reach the surface as convective
downdrafts transfer the strong horizontal momentum downward. In
addition, marginal hail may occur with a few of the stronger
updrafts, especially over parts of Texas, where steeper lapse rates
are likely to persist.
Although mid-level height changes over the southern Plains will
remain neutral or are slightly positive as the long wave trough
remains over the west, water vapor imagery indicates additional
perturbations will move northeast from the Big Bend region of Texas
over the southern Plains toward the Ozarks. This suggests potential
for additional convection to develop this afternoon. 12Z HREF
guidance and latest HRRR hourly runs are consistent with this
scenario, showing several strong organized convective bands/clusters
spreading from Texas into Arkansas later this afternoon and evening.
CAM simulated reflectivity forecasts indicate transient QLCS
structures with embedded bow echoes, suggesting a continued
potential for a few strong to locally severe wind gusts in
association with stronger storms through the evening hours.
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