Alert archive / Texas / Mesoscale Discussions in 2011

Mesoscale Discussion 835

May 21, 201118 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at May 21, 2011, 1:18 PM CDT for 18 counties in Texas. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: May 21, 2011, 1:18 PM CDT (18:18 UTC)
Expired: May 21, 2011, 3:15 PM CDT
In force: 117 min
Issued by: the Storm Prediction Center

Counties Bandera County, TX, Bosque County, TX, Burnet County, TX, Coryell County, TX, Erath County, TX, Gillespie County, TX, Hamilton County, TX, Hood County, TX, Johnson County, TX, Kerr County, TX, Lampasas County, TX, Llano County, TX, Mason County, TX, Parker County, TX, Real County, TX, San Saba County, TX, Somervell County, TX, Tarrant County, TX

The radar

The Ft Hood radar (KGRK), 141 km from the middle of the area, began a volume at 18:23 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.

Severe Thunderstorm Watch 316May 21, 1:45 PM CDT

The nearest sounding before it

Fort Worth, TX (KFWD), launched 12:00Z, 6.3 hours before the alert went out and 250 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 87 J/kg
Mixed-layer CIN: -337 J/kg
Mixed-layer LCL: 1835 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 203 m²/s²
0-3 km storm-relative helicity: 181 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

873 
ACUS11 KWNS 211818
SWOMCD
SPC MCD 211818 
TXZ000-212015-

MESOSCALE DISCUSSION 0835
NWS STORM PREDICTION CENTER NORMAN OK
0118 PM CDT SAT MAY 21 2011

AREAS AFFECTED...CNTRL TX

CONCERNING...SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY 

VALID 211818Z - 212015Z

ALTHOUGH TIMING OF TSTM INITIATION REMAINS UNCLEAR...AT LEAST AN
ISOLATED SUPERCELL OR TWO SHOULD FORM ALONG DRYLINE INVOF HILL
COUNTRY THIS AFTERNOON. THERMODYNAMIC ENVIRONMENT WILL BE QUITE
CONDUCIVE TO LARGE HAIL /SOME SIGNIFICANT/ AND WOULD LIKELY REQUIRE
A SEVERE TSTM WATCH ISSUANCE PRIOR TO 20-21Z.

18Z SUBJECTIVE SURFACE ANALYSIS PLACED DRYLINE FROM 40 E SPS S/SSWD
TO NEAR JCT AND DRT. CU FIELD INVOF DRYLINE APPEARS INCREASINGLY
AGITATED OVER THE PAST HOUR ACROSS THE TX HILL COUNTRY. MODIFIED
MORNING RAOBS/RUC FORECAST SOUNDINGS SUGGEST THE AIR MASS IS LARGELY
UNCAPPED AND HAS BECOME VERY UNSTABLE WITH MLCAPE OF 2500 TO 4000
J/KG. DESPITE NEUTRAL UPPER-LEVEL FORCING FOR ASCENT...CONTINUED
HEATING AND MODEST SURFACE CONVERGENCE ALONG THE DRYLINE SHOULD
RESULT IN A FEW TSTMS THIS AFTERNOON /SUPPORTED BY OPERATIONAL AND
CONVECTION-ALLOWING MODEL GUIDANCE/. ALTHOUGH LOW-LEVEL FLOW SHOULD
REMAIN WEAK...35-40 KT WLYS AT 500 MB WILL BE SUFFICIENT FOR
ORGANIZED UPDRAFTS. ISOLATED DISCRETE SUPERCELLS SHOULD YIELD LARGE
HAIL AS THE PRIMARY INITIAL THREAT /SOME OF WHICH MAY BE
SIGNIFICANT/.

..GRAMS.. 05/21/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

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

LAT...LON   29990016 30879909 31399864 32269823 32889796 32999731
            32619708 32039723 30679794 29849908 29409993 29430023
            29670048 29990016

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 20, 9:06 PM CDT	Mesoscale Discussion	SPC	Bowie, Camp, Cass, Cherokee, Gregg, Harrison and 7 more	114 min
May 21, 1:45 PM CDT	Severe Thunderstorm Watch	SPC	Bandera, Bell, Blanco, Bosque, Burnet, Comal and 29 more	7 hr
May 21, 3:53 PM CDT	Mesoscale Discussion	SPC	Bosque, Burnet, Coryell, Dallas, Ellis, Gillespie and 9 more	67 min
May 21, 5:42 PM CDT	Mesoscale Discussion	SPC	Bell, Blanco, Bosque, Burnet, Collin, Cooke and 28 more	2 hr

Nearby

Mesoscale Discussions in Texas, 2011 Every mesoscale discussion in 2011

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.