Mesoscale Discussion 453

Issued

Apr 28, 2021, 2:42 PM CDT (19:42 UTC)

Expired

Apr 28, 2021, 4:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

95%

Counties Bandera County, TX, Blanco County, TX, Edwards County, TX, Gillespie County, TX, Kendall County, TX, Kerr County, TX, Kimble County, TX, Kinney County, TX, Llano County, TX, Maverick County, TX, Medina County, TX, Real County, TX, Uvalde County, TX, Val Verde County, TX, Zavala County, TX

The Laughlin AFB radar (KDFX), 63 km from the middle of the area, began a volume at 19:42 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.

• Tornado Watch 120Apr 28, 3:10 PM CDT

340 
ACUS11 KWNS 281942
SWOMCD
SPC MCD 281942 
TXZ000-282145-

Mesoscale Discussion 0453
NWS Storm Prediction Center Norman OK
0242 PM CDT Wed Apr 28 2021

Areas affected...Portions of south-central TX

Concerning...Severe potential...Watch likely 

Valid 281942Z - 282145Z

Probability of Watch Issuance...95 percent

SUMMARY...Severe thunderstorms capable of producing very large hail,
damaging wind gusts, and perhaps a few tornadoes are expected to
develop this afternoon. Watch issuance will likely be needed.

DISCUSSION...Persistent low-level east-southeasterly upslope flow is
occurring this afternoon across south-central TX. This will support
convective initiation across the higher terrain of northern Mexico
adjacent to Del Rio TX. In fact, several attempts have recently
occurred along the Rio Grande River in Val Verde County, and a
lightning flash has been observed with developing convection in
adjacent northern Mexico. Rich low-level moisture, characterized by
upper 60s to low 70s surface dewpoints, is in place across this
region. This moisture coupled with strong diurnal heating and
steepening mid-level lapse rates is supporting MLCAPE of 1500-2500
J/kg east of a surface dryline.

Enhanced mid-level flow associated with an upper low over the
Southwest and northern Mexico will remain over this region through
the afternoon and evening. Related strong effective bulk shear of
50-60+ kt and long, straight hodographs above the boundary layer
will support supercells, with some potential for storm splits. Very
large hail of 2 to 3+ inches appears likely with these initially
discrete storms given the rather favorable thermodynamic and
kinematic environment. As additional storms form through the late
afternoon and into early evening, severe wind gusts may also occur
given the presence of steep low-level lapse rates where strong
diurnal heating has occurred. Although low-level winds across
south-central TX are not forecast to be very strong, there will be
ample directional shear/veering of the wind profile though the
boundary layer. This should support low-level rotation with any
supercells that can form, and isolated tornadoes appear possible.
Watch issuance will likely be needed to address this anticipated
severe threat.

..Gleason/Hart.. 04/28/2021

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

ATTN...WFO...EWX...SJT...

LAT...LON   29730153 30150129 30420067 30599987 30719900 30719844
            30429823 29959841 29229917 28569999 28570048 29010072
            29300099 29730153

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.