Alert archive / Texas / Severe Thunderstorm Watches in 2011

Severe Thunderstorm Watch 171

April 20, 201126 counties in Texas

The Storm Prediction Center issued this severe thunderstorm watch at Apr 20, 2011, 2:21 PM CDT for 26 counties in Texas. It was in force for 8 hr.

The area

The outline as issued.

The facts

Issued
Apr 20, 2011, 2:21 PM CDT (19:21 UTC)
Expired
Apr 20, 2011, 10:00 PM CDT
In force
8 hr
Issued by
the Storm Prediction Center
Largest hail expected
2.5 in
Strongest gust expected
60 kt
All 26 counties

Bandera County, TX, Bell County, TX, Blanco County, TX, Burnet County, TX, Concho County, TX, Coryell County, TX, Crockett County, TX, Edwards County, TX, Gillespie County, TX, Hamilton County, TX, Irion County, TX, Kendall County, TX, Kerr County, TX, Kimble County, TX, Lampasas County, TX, Llano County, TX, Mason County, TX, McCulloch County, TX, Menard County, TX, Mills County, TX, Real County, TX, San Saba County, TX, Schleicher County, TX, Sutton County, TX, Tom Green County, TX, Val Verde County, TX

The radar

The San Angelo radar (KSJT), 67 km from the middle of the area, began a volume at 19:23 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes
20%
One or more EF2 to EF5 tornadoes
5%
Ten or more severe wind reports
30%
One or more gusts of 65 knots or more
30%
Ten or more severe hail reports
60%
One or more hailstones of 2 inches or more
50%
Six or more combined severe hail and wind reports
90%

Warnings issued inside it

20 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

IssuedProductOfficeCountiesLasted
Apr 20, 3:22 PM CDTSevere Thunderstorm WarningSJTMenard53 min
Apr 20, 3:29 PM CDTSevere Thunderstorm WarningSJTConcho, Menard61 min
Apr 20, 3:44 PM CDTSevere Thunderstorm WarningSJTConcho, McCulloch51 min
Apr 20, 4:13 PM CDTFlash Flood WarningSJTMenard107 min
Apr 20, 4:16 PM CDTSevere Thunderstorm WarningSJTKimble, Menard59 min
Apr 20, 4:20 PM CDTSevere Thunderstorm WarningSJTIrion, Schleicher, Tom Green40 min
Apr 20, 4:28 PM CDTSevere Thunderstorm WarningSJTConcho62 min
Apr 20, 4:44 PM CDTSevere Thunderstorm WarningSJTConcho, Runnels61 min
Apr 20, 4:45 PM CDTSevere Thunderstorm WarningSJTConcho, Tom Green45 min
Apr 20, 5:04 PM CDTSevere Thunderstorm WarningSJTSchleicher, Tom Green41 min
Apr 20, 5:12 PM CDTSevere Thunderstorm WarningSJTKimble, Menard63 min
Apr 20, 5:25 PM CDTTornado WarningSJTKimble35 min
Apr 20, 5:45 PM CDTSevere Thunderstorm WarningSJTKimble45 min
Apr 20, 6:21 PM CDTSevere Thunderstorm WarningSJTKimble39 min
Apr 20, 6:41 PM CDTTornado WarningSJTKimble, Sutton49 min
Apr 20, 6:57 PM CDTSevere Thunderstorm WarningSJTKimble, Sutton63 min
Apr 20, 8:00 PM CDTSevere Thunderstorm WarningSJTCrockett, Irion60 min
Apr 20, 8:23 PM CDTSevere Thunderstorm WarningSJTSchleicher67 min
Apr 20, 8:58 PM CDTSevere Thunderstorm WarningSJTCrockett62 min
Apr 20, 9:28 PM CDTSevere Thunderstorm WarningSJTSchleicher, Sutton47 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Del Rio, TX (KDRT), launched 12:00Z, 7.4 hours before the alert went out and 168 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, Del Rio, TX at 12:00Z on 2011-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 3836 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, Del Rio, TX at 12:00Z on 2011-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 144 square meters per square second.1939Sfc1 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
3836 J/kg
Mixed-layer CIN
-184 J/kg
Mixed-layer LCL
1002 m above ground
0-6 km bulk shear
19 kt
0-1 km storm-relative helicity
144 m²/s²
0-3 km storm-relative helicity
131 m²/s²
Significant tornado parameter
0.0
Supercell composite
5.3

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 19, 7:47 PM CDTMesoscale DiscussionSPCBowie, Camp, Cass, Delta, Franklin, Hopkins and 11 more88 min
Apr 19, 9:03 PM CDTMesoscale DiscussionSPCBell, Coryell, Falls, Freestone, Henderson, Hill and 3 more57 min
Apr 19, 11:17 PM CDTMesoscale DiscussionSPCBowie, Camp, Cass, Franklin, Gregg, Harrison and 7 more58 min
Apr 19, 11:45 PM CDTSevere Thunderstorm WatchSPCBowie, Camp, Cass, Franklin, Gregg, Harrison and 6 more3 hr
Apr 20, 12:46 PM CDTMesoscale DiscussionSPCBowie, Camp, Cass, Franklin, Marion, Morris and 2 more89 min
Apr 20, 1:52 PM CDTMesoscale DiscussionSPCBell, Bosque, Brown, Burnet, Coleman, Comanche and 21 more53 min
Apr 20, 2:04 PM CDTSevere Thunderstorm WatchSPCBowie, Red River7 hr
Apr 20, 5:47 PM CDTMesoscale DiscussionSPCBlanco, Burnet, Concho, Crockett, Edwards, Gillespie and 15 more58 min

Nearby

Severe Thunderstorm Watches in Texas, 2011Every severe thunderstorm watch 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.