Mesoscale Discussion 0811
NWS Storm Prediction Center Norman OK
0148 AM CDT Thu May 21 2026
Areas affected...South Texas
Concerning...Severe potential...Watch unlikely
Valid 210648Z - 210845Z
Probability of Watch Issuance...20 percent
SUMMARY...Thunderstorms will continue this morning across south
Texas within a very unstable airmass. An isolated damaging wind or
hail report may be possible this morning, but a more
organized/widespread severe threat is not anticipated.
DISCUSSION...Thunderstorms are moving east out of northern Mexico
into portions of south Texas this morning. Recent satellite imagery
indicates renewed cooling of cloud tops indicative of increasing
vigor with the thunderstorm updrafts. This is reflected in recent
MRMS CAPPI data, which recently showed a general trend for more
thunderstorm cores to exceed 35 dbz at 16kft, although the last
couple of images have trended downward.
These thunderstorms appear to be aided by a weak, convectively
augmented mid-level vorticity maximum/short-wave trough moving
across northeast Mexico and an upper-level jet streak moving through
the basal region of the upper-level long-wave trough across western
North America. This seasonably strong westerly mid- and upper-level
flow, when combined with weak easterly low-level flow results in
effective shear across south Texas between 30 and 40 knots, with
locally higher values.
Thermodynamically, the area remains very unstable with MUCAPE
ranging from upper 2000s J/kg (west) to nearly 4000 J/kg along the
coast. RAP and HRRR 1-hour point forecast soundings across the
region show relatively poor low-level and nearly moist adiabatic
lapse rates from nearly 700-millibars and above.
Given the modestly sheared, very unstable environment, the
expectation is for the loosely organized ongoing convection to
sustain itself through the morning as it moves east across portions
of south Texas, perhaps growing upscale into a linear MCS. The poor
low-level lapse rates should limit the overall damaging wind
potential, but the degree of instability and moist mid-/upper-level
profiles suggest at least some potential for a water-laden downburst
capable of producing locally damaging thunderstorm winds. An
isolated large hail report cannot be ruled out given the degree of
instability.
A watch is currently not expected given the anticipated isolated
nature of the damaging wind potential. However, the region will
continue to be monitored this morning.
..Marsh/Gleason.. 05/21/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CRP...EWX...BRO...
LAT...LON 27709964 28329971 28659948 28709840 28669690 28309639
27839683 27339709 26839711 26189697 25869696 25769735
26019829 26399921 27029960 27709964
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
Source link