Alert archive / Texas / Mesoscale Discussions in 2012

Mesoscale Discussion 2004

September 28, 20128 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Sep 28, 2012, 10:20 PM CDT for 8 counties in Texas. It was in force for 85 min.

The area

The outline as issued.

The facts

Issued
Sep 28, 2012, 10:20 PM CDT (03:20 UTC)
Expired
Sep 28, 2012, 11:45 PM CDT
In force
85 min
Issued by
the Storm Prediction Center
Chance of a watch
20%

Counties Dimmit County, TX, Frio County, TX, La Salle County, TX, Maverick County, TX, Medina County, TX, Uvalde County, TX, Webb County, TX, Zavala County, TX

The radar

The Laughlin AFB radar (KDFX), 85 km from the middle of the area, began a volume at 03:23 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 nearest sounding before it

Del Rio, TX (KDRT), launched 00:00Z, 3.3 hours before the alert went out and 136 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 00:00Z on 2012-09-29Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 933 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 00:00Z on 2012-09-29The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 85 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
933 J/kg
Mixed-layer CIN
-5 J/kg
Mixed-layer LCL
522 m above ground
0-6 km bulk shear
26 kt
0-1 km storm-relative helicity
85 m²/s²
0-3 km storm-relative helicity
177 m²/s²
Significant tornado parameter
0.4
Supercell composite
2.9

Open this sounding in Storm Lab

The text

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

089 
ACUS11 KWNS 290320
SWOMCD
SPC MCD 290320 
TXZ000-290445-

MESOSCALE DISCUSSION 2004
NWS STORM PREDICTION CENTER NORMAN OK
1020 PM CDT FRI SEP 28 2012

AREAS AFFECTED...LOWER RIO GRANDE VALLEY OF SOUTH TX

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 290320Z - 290445Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...IN ADDITION TO HEAVY RAINFALL RATES /1-2 INCH PER HOUR/
ACROSS PARTS OF THE LOWER RIO GRANDE VALLEY AND SOUTH CENTRAL TX
DURING THE NEXT SEVERAL HOURS...AN ISOLATED STRONG TO SEVERE STORM
WILL BE POSSIBLE.  THE GREATEST THREATS WITH THE STRONGER ACTIVITY
WILL BE A STRONG WIND GUST AND/OR A BRIEF TORNADO.  

THE LACK OF DISCRETE CELLULAR ACTIVITY...GENERALLY SLOW STORM
MOTIONS...AND THE LACK OF SUSTAINED/DEEPER ROTATIONAL COUPLETS
PRECLUDES THE ISSUANCE OF A WATCH AT THIS TIME.  HOWEVER...
CONVECTIVE TRENDS WILL BE MONITORED.

DISCUSSION...TRENDS IN EVENING RADAR IMAGERY ACROSS SOUTH CENTRAL TX
INTO THE ADJACENT PART OF MEXICO INDICATED SOME WEAK LOW LEVEL
ROTATION EMBEDDED WITHIN TWO BANDS OF STORMS IN THIS REGION.  ONE
AREA EXTENDED FROM NRN WEBB COUNTY TX SSWWD INTO ADJACENT MEXICO...
WITH THE SECOND BAND APPROACHING THE LOWER RIO GRANDE RIVER FROM ERN
COAHUILA MEXICO.  CLOUD TOP COOLING ACROSS THE DISCUSSION AREA IS
LOCATED AHEAD OF A MORE PRONOUNCED SHORTWAVE TROUGH TRACKING TO THE
ENE ACROSS THE WRN/NRN PARTS OF COAHUILA MEXICO. IMPLIED ASCENT
AHEAD OF THIS FEATURE WILL CONTINUE TO SUPPORT ADDITIONAL CONVECTION
WITHIN AN AIR MASS UNDERGOING WARM/MOIST CLOUD PROCESSES...GIVEN
TROPICAL PW VALUES EXCEEDING 2.2 TO 2.4 INCH PER 00Z SOUNDINGS. 
DESPITE WEAK LAPSE RATES...THE HIGH MOISTURE CONTENT AIR IS
CONTRIBUTING TO MLCAPE OF 1000-1500 J/KG.  VERTICALLY VEERING WIND
PROFILES AND AN INCREASE IN SWLY MIDLEVEL WINDS AND LOW LEVEL WINDS
WITH THE APPROACH OF THE CENTRAL MEXICO TROUGH SUGGEST STRONGER BULK
SHEAR INTO S TX.  OBJECTIVE ANALYSES SUGGEST THIS TREND IS UNDERWAY
GIVEN EFFECTIVE BULK SHEAR ALREADY RANGING FROM 35-40 KT.  

DESPITE THESE FAVORABLE KINEMATICS...THE WEAK LAPSE RATES COULD TEND
TO LIMIT SUSTAINED STORMS UPDRAFTS.  HOWEVER...THESE KINEMATICS
WITHIN MODERATE INSTABILITY SUGGEST A FEW STRONGER STORMS COULD
PROVE FAVORABLE IN PRODUCING AN ISOLATED...THOUGH ENHANCED...WIND
THREAT THROUGH MOISTURE LADEN DOWNDRAFTS AND/OR A BRIEF TORNADO
GIVEN AN INCREASE IN LOW LEVEL HODOGRAPH CURVATURE.

..PETERS/CARBIN.. 09/29/2012

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

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

LAT...LON   29519986 29619906 29449860 28529860 27629914 27479967
            28130030 28610059 29280056 29519986

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 29, 5:23 PM CDTMesoscale DiscussionSPCAransas, Austin, Calhoun, Colorado, DeWitt, Fayette and 9 more97 min

Nearby

Mesoscale Discussions in Texas, 2012Every mesoscale discussion in 2012

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.