Mesoscale Discussion 0807
NWS Storm Prediction Center Norman OK
0354 PM CDT Sun May 21 2017
Areas affected...Deep South TX
Concerning...Severe potential...Watch possible
Valid 212054Z - 212230Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated severe thunderstorms, with a threat for large
hail and damaging winds, will spread into portions of Deep South
Texas over the next several hours.
DISCUSSION...Deep convection has gradually advected east of the
highest terrain of northern Mexico. A large cluster of
thunderstorms has now propagated toward the Rio Grande Valley and a
few robust storms will soon move east of the international border.
The strongest storm, over Webb County, likely contains severe hail
and is propagating slowly east just north of a stationary front.
For some time the eastern-most convection has struggled to maintain
intensity as it shifts east of the border; however, boundary-layer
heating across Deep South TX has contributed to significant buoyancy
as temperatures are near 90F just south of the front. There is some
concern the storms over Webb County, and adjacent convection west of
the river, may propagate into a small corridor of
Webb/Zapata/Duval/Jim Hogg counties. Given the limited extent of
influence it's not clear whether a WW will be issued. Even so,
large hail and damaging winds could accompany this activity.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 28259967 28069879 27439835 26609862 26599941 27630028