Mesoscale Discussion 1857

Issued

Oct 13, 2021, 7:50 PM CDT (00:50 UTC)

Expired

Oct 13, 2021, 9:45 PM CDT

In force

115 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

Counties Atascosa County, TX, Bexar County, TX, Comal County, TX, Duval County, TX, Frio County, TX, Guadalupe County, TX, Jim Hogg County, TX, La Salle County, TX, McMullen County, TX, Webb County, TX, Wilson County, TX, Zapata County, TX

The Corpus Christi radar (KCRP), 139 km from the middle of the area, began a volume at 00:53 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

578 
ACUS11 KWNS 140050
SWOMCD
SPC MCD 140050 
TXZ000-140245-

Mesoscale Discussion 1857
NWS Storm Prediction Center Norman OK
0750 PM CDT Wed Oct 13 2021

Areas affected...Parts of Deep South Texas and the adjacent lower
Rio Grande Valley

Concerning...Severe potential...Watch unlikely 

Valid 140050Z - 140245Z

Probability of Watch Issuance...20 percent

SUMMARY...Increasing thunderstorm development near and just east of
the Interstate 35 corridor of Deep South Texas will intensify
further during the next few hours, and perhaps occasionally pose a
risk for severe hail and locally strong surface gusts.  It seems
unlikely that a severe weather watch will be needed, but trends will
continue to be monitored.

DISCUSSION...Warm elevated mixed-layer air has suppressed deep
convective development into early evening across the lower Rio
Grande Valley, but thunderstorms are now initiating around Laredo
northward into the San Antonio area.  It appears that this is being
supported by another mid-level perturbation emerging from the
Mexican Plateau, which is forecast to be accompanied by substantive
mid-level cooling overspreading the Rio Grande River vicinity
through a corridor along and east of Interstate 35 between now and
03-05Z.  This will coincide with a narrow plume of tropical moisture
return (including PW of 2-2.25+ inches) from the the western Gulf of
Mexico, which is contributing to large CAPE in the presence of
modestly steep mid-level lapse rates.

Given this thermodynamic environment, shear associated with a belt
of 30-40 kt south-southwesterly flow in the 700-500 mb layer may be
sufficient to support the evolution of a few supercell structures. 
While modest to weak southerly lower-level flow probably will remain
a limiting factor concerning the overall severe weather potential,
stronger cells might still be able to occasional pose a risk for
severe hail hail and locally strong surface gusts.

..Kerr/Guyer.. 10/14/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...CRP...EWX...BRO...

LAT...LON   27169964 28419938 29389882 30029835 29819768 28519822
            27169862 26059930 27169964

Mesoscale Discussions in Texas, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.