Alert archive / Texas / Mesoscale Discussions in 2011

Mesoscale Discussion 504

April 21, 201122 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Apr 21, 2011, 2:19 PM CDT for 22 counties in Texas. It was in force for 56 min.

The area

The outline as issued.

The facts

Issued: Apr 21, 2011, 2:19 PM CDT (19:19 UTC)
Expired: Apr 21, 2011, 3:15 PM CDT
In force: 56 min
Issued by: the Storm Prediction Center

All 22 counties

Coke County, TX, Crane County, TX, Crockett County, TX, Fisher County, TX, Glasscock County, TX, Howard County, TX, Irion County, TX, Midland County, TX, Mitchell County, TX, Nolan County, TX, Pecos County, TX, Reagan County, TX, Runnels County, TX, Schleicher County, TX, Scurry County, TX, Sterling County, TX, Sutton County, TX, Taylor County, TX, Terrell County, TX, Tom Green County, TX, Upton County, TX, Val Verde County, TX

The radar

The San Angelo radar (KSJT), 126 km from the middle of the area, began a volume at 19:17 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 176Apr 21, 3:05 PM CDT

The nearest sounding before it

Midland Regional, TX (KMAF), launched 12:00Z, 7.3 hours before the alert went out and 150 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: 695 J/kg
Mixed-layer CIN: -359 J/kg
Mixed-layer LCL: 968 m above ground
0-6 km bulk shear: 33 kt
0-1 km storm-relative helicity: 240 m²/s²
0-3 km storm-relative helicity: 283 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 3.4

Open this sounding in Storm Lab

The text

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

024 
ACUS11 KWNS 211920
SWOMCD
SPC MCD 211919
TXZ000-212015-

MESOSCALE DISCUSSION 0504
NWS STORM PREDICTION CENTER NORMAN OK
0219 PM CDT THU APR 21 2011

AREAS AFFECTED...TX PECOS RIVER VALLEY

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 211919Z - 212015Z

STORM INITIATION IS EXPECTED WITHIN THE NEXT HOUR OR SO ACROSS THE
TX PECOS RIVER VALLEY.  SUPERCELLS CAPABLE OF LARGE TO VERY LARGE
HAIL AND DMGG WINDS WILL BE THE PRIMARY HAZARDS.  A WW MAY BE
REQUIRED TO ADDRESS THIS THREAT AND THE 20Z CONVECTIVE OUTLOOK
UPDATE WILL INCLUDE THIS AREA IN A SLIGHT RISK.

WATER VAPOR TRENDS THE PAST FEW HOURS SHOWS A WEAK IMPULSE MOVING
ACROSS ERN NM AND PARTS OF W TX.  THIS IS EVIDENT IN WSM PROFILER
TIME SERIES WITH FLOW INCREASING BY 20 KTS IN THE MID-UPPER LEVELS
SINCE THIS MORNING.  ASCENT ASSOCIATED WITH THIS FEATURE...IMPLIED
BY EWD MOVING BROKEN CIRRUS SHIELD...IS NOW SPREADING TOWARDS THE S
PLAINS AND THE LOWER PECOS RIVER VALLEY.  LATEST SURFACE ANALYSIS
SHOWS 1MB/HR SURFACE PRESSURE FALLS THE PAST FEW HOURS SEEMINGLY
REFLECTIVE OF THE UPPER FEATURE WITH RICH LOW LEVEL MOISTURE
CHARACTERIZED BY MID 60S DEWPOINTS HOLDING ACROSS THE LOWER PECOS
RIVER VALLEY IN SWRN TX.  STRONG HEATING ACROSS THE
REGION...PREFERABLY FAVORING HIGHER TERRAIN/ HAS ESSENTIALLY
WEAKENED THE REMAINING CAP.  AS SUCH...EXPECTING STORM INITIATION BY
20Z NEAR THE GLASS MTNS AND FST.

VERY STEEP LAPSE RATE ENVIRONMENT ATOP THE AFOREMENTIONED MOIST
BOUNDARY LAYER HAS LED TO A VERY UNSTABLE AIRMASS /3500 J/KG MLCAPE
PER OBJECTIVE ANALYSIS/.  MOIST SELY UPSLOPE FLOW UNDERNEATH
INCREASING DEEP LAYER SHEAR WILL BE SUPPORTIVE OF A SUPERCELL WIND
PROFILE AND RESULT IN STORMS RAPIDLY DEVELOPING AND BEING CAPABLE OF
LARGE TO VERY LARGE HAIL AND DMGG WINDS ONCE SUPERCELL STRUCTURE IS
ATTAINED.  ALTHOUGH ONLY ISOLD STORM COVERAGE IS EXPECTED...THE
NATURE OF THE THREAT MAY WARRANT A WW ISSUANCE WITHIN THE NEXT HOUR
OR TWO.

..SMITH.. 04/21/2011

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

ATTN...WFO...EWX...SJT...LUB...MAF...

LAT...LON   29900301 30730358 31250312 33060072 33070003 32419974
            30030036 29490042 28970088 29060246 29900301

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 20, 7:00 PM CDT	Mesoscale Discussion	SPC	Archer, Callahan, Coleman, Eastland, Jack, Palo Pinto and 5 more	60 min
Apr 21, 3:03 PM CDT	Severe Thunderstorm Watch	SPC	Borden, Brewster, Brown, Callahan, Coke, Coleman and 23 more	7 hr
Apr 21, 3:23 PM CDT	Mesoscale Discussion	SPC	Camp, Collin, Cooke, Dallas, Delta, Denton and 25 more	67 min
Apr 21, 5:10 PM CDT	Mesoscale Discussion	SPC	Borden, Brewster, Coke, Crockett, Fisher, Glasscock and 21 more	65 min

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.