Alert archive / Texas / Mesoscale Discussions in 2021

Mesoscale Discussion 684

May 19, 202111 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at May 19, 2021, 3:32 AM CDT for 11 counties in Texas. It was in force for 118 min.

The area

The outline as issued.

The facts

Issued
May 19, 2021, 3:32 AM CDT (08:32 UTC)
Expired
May 19, 2021, 5:30 AM CDT
In force
118 min
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch possible
Chance of a watch
40%

Counties Brooks County, TX, Dimmit County, TX, Duval County, TX, Hidalgo County, TX, Jim Hogg County, TX, Jim Wells County, TX, La Salle County, TX, McMullen County, TX, Starr County, TX, Webb County, TX, Zapata County, TX

The radar

The Corpus Christi radar (KCRP), 150 km from the middle of the area, began a volume at 08:36 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.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

The nearest sounding before it

Corpus Christi, TX (KCRP), launched 00:00Z, 8.5 hours before the alert went out and 165 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Corpus Christi, TX at 00:00Z on 2021-05-19Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2386 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Corpus Christi, TX at 00:00Z on 2021-05-19The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 59 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
2386 J/kg
Mixed-layer CIN
-17 J/kg
Mixed-layer LCL
721 m above ground
0-6 km bulk shear
22 kt
0-1 km storm-relative helicity
59 m²/s²
0-3 km storm-relative helicity
114 m²/s²
Significant tornado parameter
0.8
Supercell composite
6.4

Open this sounding in Storm Lab

The text

As transmitted.

711 
ACUS11 KWNS 190832
SWOMCD
SPC MCD 190832 
TXZ000-191030-

Mesoscale Discussion 0684
NWS Storm Prediction Center Norman OK
0332 AM CDT Wed May 19 2021

Areas affected...portions of south Texas

Concerning...Severe potential...Watch possible 

Valid 190832Z - 191030Z

Probability of Watch Issuance...40 percent

SUMMARY...Thunderstorms may develop east of the Rio Grande early
this morning, bringing a threat for damaging gusts and hail.

DISCUSSION...At 08z, an outflow boundary stretched westward from
just north of Corpus Christi to just north of Laredo. South of this
boundary, surface dewpoints are generally in the low to mid 70s F
beneath very steep midlevel lapse rates (per 06z BRO RAOB). This is
contributing to strong instability, with MLCAPE values greater than
2500 J/kg present. A thunderstorm cluster has been developing near
the higher terrain across the Rio Grande in Mexico. This activity
will gradually spread east over the few several hours. 

While effective shear is somewhat marginal across south Texas, a
modest southerly low level jet coupled with strong instability
should be sufficient for some organized cluster to track along/east
of the Rio Grande this morning. Some CAMs depict an organized bow
moving across this area, though timing of this feature remains
somewhat uncertain as current convection is developing earlier than
what has been indicated in forecast guidance. Should an organized
cluster emerge, damaging gusts (and perhaps hail with any
semi-discrete cells given very steep midlevel lapse rates) will be
possible through the morning hours. Convective trends will be
monitored and a severe thunderstorm watch may be needed in the next
couple of hours.

..Leitman/Hart.. 05/19/2021

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

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

LAT...LON   26539933 26909965 28090041 28300043 28460034 28629979
            28669943 28599866 28309806 28149790 27799774 27119776
            26469799 26049830 26099873 26219892 26539933

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 18, 7:34 PM CDTTornado WatchSPCAustin, Bee, Brazoria, Chambers, Colorado, Fort Bend and 17 more6 hr
May 18, 8:00 PM CDTMesoscale DiscussionSPCCherokee, Gregg, Harrison, Marion, Nacogdoches, Panola and 4 more60 min
May 18, 8:54 PM CDTMesoscale DiscussionSPCAustin, Fort Bend, Harris, Jackson, Montgomery, Waller and 1 more96 min
May 18, 10:39 PM CDTMesoscale DiscussionSPCHardin, Jasper, Jefferson, Newton, Orange, Tyler96 min
May 18, 11:00 PM CDTMesoscale DiscussionSPCDimmit, Duval, Jim Hogg, La Salle, Webb, Zapata90 min
May 19, 5:24 AM CDTSevere Thunderstorm WatchSPCBrooks, Cameron, Duval, Hidalgo, Jim Hogg, Jim Wells and 8 more8 hr
May 19, 7:09 AM CDTMesoscale DiscussionSPCHidalgo, Jim Hogg, Starr96 min
May 19, 8:46 AM CDTMesoscale DiscussionSPCBrooks, Cameron, Hidalgo, Kenedy, Willacy89 min
May 19, 2:10 PM CDTMesoscale DiscussionSPCCallahan, Coke, Coleman, Concho, Crane, Crockett and 24 more3 hr
May 19, 6:06 PM CDTMesoscale DiscussionSPCCrane, Crockett, Ector, Glasscock, Irion, Midland and 6 more84 min

Nearby

Mesoscale Discussions in Texas, 2021Every mesoscale discussion in 2021

Sources

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.