SPC AC 121955
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Mon Apr 12 2021
Valid 122000Z - 131200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON THROUGH LATE THIS EVENING ACROSS THE EDWARDS PLATEAU AND
A few afternoon and evening thunderstorms will produce isolated very
large hail and locally damaging winds across the Edwards Plateau and
vicinity in Texas.
No changes have been made to the Slight Risk area across the Edwards
Plateau region of TX. It appears that convective initiation will
probably occur within the next few hours (by 22-23Z) between San
Angelo and Junction TX. Visible satellite imagery shows a cumulus
field has developed across this area in the vicinity of a cold
front. Latest RAP forecast soundings suggest minimal capping
remaining by 22Z, and weak low-level convergence along the front
should be enough to initiate at least a couple of storms.
Environmental conditions still appear favorable for isolated very
large hail with any supercells that can form this afternoon/early
evening, as moderate to strong instability, steep mid-level lapse
rates, and sufficient deep-layer shear will all be present.
Occasional strong to severe wind gusts from convective downdrafts
may also occur as low-level lapse rates continue to steepen
along/south of the cold front.
.PREV DISCUSSION... /ISSUED 1118 AM CDT Mon Apr 12 2021/
...Central TX area late this afternoon into tonight...
A series of subtle southern-stream shortwave troughs will move
east-northeastward from northern Mexico/far west TX/southern NM over
western/northern TX and OK through tonight. At the surface, a cold
front will continue to move southward across north and central TX,
while low-level moisture spreads north-northwestward in advance of
the front. Satellite imagery suggests that the strongest surface
heating will occur south of I-20, where afternoon temperatures of
85-90 and boundary-layer dewpoints near 60 will support MLCAPE of
2500 J/kg. Widely scattered thunderstorm development is expected in
the zone of low-level ascent and minimized convective inhibition
along the front late this afternoon across the Edwards Plateau, with
the large buoyancy and relatively straight/long hodographs and
midlevel lapse rates greater than 8 C/km favoring splitting
supercells capable of producing isolated very large hail (greater
than 2.5 inches in diameter) and isolated damaging winds. Some of
the left-moving storms could progress as far as north TX prior to
weakening this evening, and additional elevated convection (with a
low-end hail threat) may form atop the frontal surface early tonight
from north TX into southeastern OK.
Farther south, supercell development is also expected along the east
slope of the Serranias del Burro (west of Del Rio), and the storms
will make it near or just across the Rio Grande before weakening.
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