SPC AC 130828
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0228 AM CST Fri Jan 13 2017
Valid 151200Z - 161200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WEST AND CENTRAL TEXAS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN PLAINS...
A severe threat with large hail and isolated wind damage will be
possible on Sunday across parts of the southern Plains.
An upper-level low will move northeastward across southern New
Mexico on Sunday as a negatively tilted upper-level trough moves
into the Rio Grande Valley. Thunderstorm activity could be ongoing
just ahead of the upper-level trough across far west Texas into far
southeastern New Mexico at the start of the period. The models are
consistent with moving this convection slowly eastward across the
southern high Plains during the day on Sunday. At the surface, a
trough is forecast to move into west Texas as a cold front advances
from west to east from the Pecos Valley into western parts of the
Texas Hill Country. Surface dewpoints ahead of the front will likely
be 50s F with weak instability developing by afternoon.
The greatest potential for a severe threat would be just ahead of
the mid-level jet on the southern end of a cluster of storms
forecast to be located near San Angelo by afternoon. This threat
would extend southward toward the Rio Grande Valley where storms are
forecast to have access to the greatest instability. NAM forecast
soundings valid 00Z/Monday just to the south of San Angelo show a
surface dewpoint of 57 F, MLCAPE of 700 J/kg, 0-6 km shear near 60
kts and steep lapse rates from 700 to 500 mb. This should be enough
for a supercell threat with isolated large hail associated with the
stronger updrafts. A veering wind profile with height may also help
downdrafts produce damaging wind gusts. Further to the north into
parts of northwest Texas, surface dewpoints will not be as high but
strong deep-layer shear and steep mid-level lapse rates may be
enough for hail and isolated damaging wind gusts especially if a
line of storms can organize during the late afternoon.
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