Alert archive / Texas / Mesoscale Discussions in 2007

Mesoscale Discussion 2152

November 21, 200715 parishes in Louisiana; 19 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Nov 21, 2007, 1:32 PM CST for 15 parishes in Louisiana; 19 counties in Texas. It was in force for 118 min.

The area

The outline as issued.

The facts

Issued: Nov 21, 2007, 1:32 PM CST (19:32 UTC)
Expired: Nov 21, 2007, 3:30 PM CST
In force: 118 min
Issued by: the Storm Prediction Center

All 34 counties

Beauregard Parish, LA, Bienville Parish, LA, Bossier Parish, LA, Caddo Parish, LA, Claiborne Parish, LA, De Soto Parish, LA, Jackson Parish, LA, Lincoln Parish, LA, Natchitoches Parish, LA, Red River Parish, LA, Sabine Parish, LA, Union Parish, LA, Vernon Parish, LA, Webster Parish, LA, Winn Parish, LA, Angelina County, TX, Austin County, TX, Grimes County, TX, Hardin County, TX, Jasper County, TX, Liberty County, TX, Montgomery County, TX, Nacogdoches County, TX, Newton County, TX, Panola County, TX, Polk County, TX, Sabine County, TX, San Augustine County, TX, San Jacinto County, TX, Shelby County, TX, Trinity County, TX, Tyler County, TX, Walker County, TX, Waller County, TX

The radar

The Shreveport radar (KSHV), 169 km from the middle of the area, began a volume at 19:35 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 735Nov 21, 2:30 PM CST

The nearest sounding before it

Shreveport, LA (KSHV), launched 12:00Z, 7.5 hours before the alert went out and 177 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: 642 J/kg
Mixed-layer CIN: -45 J/kg
Mixed-layer LCL: 615 m above ground
0-6 km bulk shear: 34 kt
0-1 km storm-relative helicity: 143 m²/s²
0-3 km storm-relative helicity: 171 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.3

Open this sounding in Storm Lab

The text

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

000 
ACUS11 KWNS 211932
SWOMCD
SPC MCD 211932 
LAZ000-TXZ000-212130-

MESOSCALE DISCUSSION 2152
NWS STORM PREDICTION CENTER NORMAN OK
0132 PM CST WED NOV 21 2007

AREAS AFFECTED...E TX...WCNTRL/NWRN LA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 211932Z - 212130Z

19Z MESOANALYSIS PLACES A PRE-FRONTAL TROUGH EXTENDING FROM NEAR
KSHV SWWD TO KCLL THEN INTO SCNTRL TX NEAR KSAT.  SSWLY LOW-LEVEL
FLOW WAS IMPINGING ON THIS BOUNDARY...MAXIMIZING LOW-LEVEL
CONVERGENCE PRIMARILY NE OF KCLL.  AT THE SAME TIME...WATER VAPOR
IMAGERY DEPICTED THE LEADING EDGE OF STRONGER LARGE SCALE ASCENT
MOVING ACROSS SCNTRL TX...DEEPENING THE CIRCULATION VCNTY THE TROUGH
AND CONTRIBUTING TO TSTM DEVELOPMENT.  

DOWNSTREAM AIR MASS HAD BECOME MODERATELY UNSTABLE WITH MLCAPES OF
1500-2000 J/KG OWING TO PERSISTENT MOISTURE ADVECTION AND STRONG
HEATING.  THIS WILL SUPPORT A CONTINUED STRONG TSTM THREAT. 
VERTICAL SHEAR...HOWEVER...IS COMPARATIVELY WEAKER THAN AT POINTS
FARTHER EAST AND NORTH.  PAT/LDB PROFILERS SUGGEST THAT DEEP LAYER
SHEAR THROUGH ABOUT 6 KM IS LESS THAN 25 KTS ATTM.  SOME IMPROVEMENT
IN THE SHEAR MAY OCCUR LATER THIS AFTN/EVE TO SUPPORT  BRIEF
SUPERCELL STRUCTURES...BUT IT APPEARS STORMS WILL HAVE A TOUGH TIME
REMAINING ORGANIZED AS THEY MOVE ESEWD INTO LA AND THE UPR TX. 
GIVEN IMPROVING MID-LVL LAPSE RATES...MORE ROBUST STORMS MAY PRODUCE
HAIL ALONG WITH THE THREAT FOR ISOLD DMGG WIND GUSTS THROUGH EARLY
THIS EVENING.

..RACY.. 11/21/2007

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

ATTN...WFO...LCH...SHV...HGX...

30539637 31069565 32479423 32929369 32939226 30669294
29889558 29679640

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Nov 21, 11:17 AM CST	Mesoscale Discussion	SPC	Bossier, Caddo, Claiborne, Lincoln, Morehouse, Union and 1 more	118 min
Nov 21, 12:24 PM CST	Mesoscale Discussion	SPC	Ascension, East Baton Rouge, East Feliciana, Iberville, Lafayette, Livingston and 13 more	2 hr
Nov 21, 2:29 PM CST	Severe Thunderstorm Watch	SPC	Beauregard, Bienville, Bossier, Caddo, Caldwell, Claiborne and 17 more	8 hr
Nov 21, 5:10 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, Beauregard and 50 more	65 min
Nov 21, 5:29 PM CST	Severe Thunderstorm Watch	SPC	Acadia, Allen, Ascension, Avoyelles, Calcasieu, Catahoula and 19 more	6 hr

Nearby

Mesoscale Discussions in Texas, 2007 Mesoscale Discussions in Louisiana, 2007 Every mesoscale discussion in 2007

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.