SPC AC 180728
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0228 AM CDT Mon Mar 18 2024
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE WEDNESDAY
AFTERNOON AND EVENING ACROSS PARTS OF THE TEXAS PANHANDLE AND
ADJACENT WESTERN OKLAHOMA...AND WEDNESDAY NIGHT ACROSS THE TEXAS
HILL COUNTRY VICINITY...
...SUMMARY...
A couple clusters of thunderstorm activity may develop across the
southern Great Plains late Wednesday afternoon into Wednesday night.
Some of these storms could be accompanied by a risk for severe hail
and gusty winds.
...Synopsis...
As a significant short wave impulse, emerging from the base of
larger-scale mid-level troughing centered near the Atlantic
Seaboard, accelerates into the northern Atlantic, models continue to
indicate that a less amplified split flow will gradually evolve east
of the Rockies through the western Atlantic. Another vigorous short
wave trough is forecast to continue digging within one branch,
east-southeast of the Upper Midwest and Great Lakes region through
much of the Northeast by the end of the period. It appears that the
leading edge of an associated reinforcing low-level cold intrusion
may advance through the southern Mid Atlantic coast vicinity and
Tennessee Valley by 12Z Thursday, while advancing more slowly
southward through the Ozark Plateau and central Great Plains.
In another branch, a low amplitude wave emerging from the Southwest
is forecast to progress into a lingering (but more weakly) confluent
regime to the lee of the southern Rockies. It appears that surface
troughing across the southern Great Plains will remain weak, with
little in the way of substantive surface cyclogenesis. But an area
of lower pressure may form in association with a remnant cyclonic
vorticity center progressing into the Texas Panhandle vicinity by
late Wednesday afternoon.
In the wake of a prior intrusion of cool/dry air through much of the
Gulf Basin, guidance continues to indicate that low-level moisture
return off a modifying Gulf boundary layer will be limited, with
better boundary-layer moisture not reaching the lower Rio Grande
Valley/Texas coast until Wednesday night.
...Texas Panhandle vicinity...
There is considerable spread concerning the evolution and
progression of the approaching mid-level perturbation and the
possible weak surface low development. But guidance generally
suggests that forcing for ascent near/east of the low may ultimately
support a developing cluster of thunderstorms by Wednesday evening.
Preceding this development, surface dew points near the low may not
increase much beyond 50 F. But, with daytime heating, a well-mixed
boundary layer may become modestly deep, with CAPE increasing to
around 500 J/kg, and perhaps locally up to 1000 J/kg, beneath
relatively cold mid-level air including 500 mb temperatures around
-20 to -22 C. Although lower/mid-tropospheric wind fields and
deep-layer shear are forecast to become modest, at best, the
environment may become supportive of strong initial convection which
may pose a risk for marginally severe hail and wind.
...Central/Southern Texas...
Beneath stronger southwesterly mid-level flow, more supportive of
potential for organized severe convection, warm elevated mixed-layer
air (based near or just above 850 mb) appears likely to strongly
inhibit vigorous convective development, at least into Wednesday
evening. Thereafter, mid/upper forcing for ascent and cooling with
the approaching trough may sufficiently erode the inhibition to
support thunderstorm initiation, with guidance generally suggesting
highest probabilities across the Hill Country vicinity. Based on
NAM forecast soundings, among other output, boundary-layer moisture
may not be sufficient to support more than weak CAPE. But some
severe hail in stronger storms may not be entirely out of the
question, before convection becomes more widespread.
..Kerr.. 03/18/2024
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