Alert archive / Louisiana / Mesoscale Discussions in 2009

Mesoscale Discussion 1721

July 30, 200930 parishes in Louisiana; 8 counties in Mississippi; 5 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Jul 30, 2009, 10:12 AM CDT for 30 parishes in Louisiana; 8 counties in Mississippi; 5 counties in Texas. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Jul 30, 2009, 10:12 AM CDT (15:12 UTC)
Expired: Jul 30, 2009, 12:15 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center

All 43 counties

Allen Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Bienville Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, De Soto Parish, LA, East Carroll Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Lincoln Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Red River Parish, LA, Richland Parish, LA, Sabine Parish, LA, Tensas Parish, LA, Vernon Parish, LA, West Carroll Parish, LA, West Feliciana Parish, LA, Winn Parish, LA, Adams County, MS, Amite County, MS, Claiborne County, MS, Franklin County, MS, Issaquena County, MS, Jefferson County, MS, Warren County, MS, Wilkinson County, MS, Jasper County, TX, Newton County, TX, Sabine County, TX, San Augustine County, TX, Shelby County, TX

The nearest sounding before it

Shreveport, LA (KSHV), launched 12:00Z, 3.2 hours before the alert went out and 156 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: 2304 J/kg
Mixed-layer CIN: -5 J/kg
Mixed-layer LCL: 537 m above ground
0-6 km bulk shear: 13 kt
0-1 km storm-relative helicity: 4 m²/s²
0-3 km storm-relative helicity: 71 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.

050 
ACUS11 KWNS 301513
SWOMCD
SPC MCD 301512 
MSZ000-LAZ000-TXZ000-301715-

MESOSCALE DISCUSSION 1721
NWS STORM PREDICTION CENTER NORMAN OK
1012 AM CDT THU JUL 30 2009

AREAS AFFECTED...ECNTRL TX...NRN/CNTRL LA AND WCNTRL MS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 301512Z - 301715Z

REMNANT FORWARD FLANK OF NOCTURNAL MCS WAS ATTEMPTING TO INTENSIFY
OVER FAR ECNTRL TX AS A SMALL LINE SEGMENT.  DOWNSTREAM AIR MASS
WILL MODESTLY HEAT THROUGH THE AFTN GIVEN BREAKS IN MID/HIGH CLOUDS.
 IN FACT...MODIFICATION OF 12Z SOUNDINGS ALREADY SUGGESTS 2000-2500
J/KG OF MLCAPE AND MINIMAL MLCINH.  FORCING ASSOCD WITH THE
MCV...VERY MOIST AIR MASS IN PLACE AND CONTINUED DESTABILIZATION OF
THE BOUNDARY LAYER WILL CONTRIBUTE TO BOTH A FURTHER INTENSIFICATION
OF THE LINE AND THE ISOLD CELLS DEVELOPING AHEAD OF IT.

UPSTREAM VWP/PROFILERS SAMPLED ABOUT 40-50 KTS OF FLOW ABOVE H85 IN
WAKE OF THE MCV AND GIVEN THE MAINTENANCE OF A 30 KT H925-H85 SLY
LLJ AHEAD OF THE FEATURE...ADDITIONAL STORM ORGANIZATION CAN BE
EXPECTED.  PRIMARY THREAT WILL BE DMGG WINDS...ESPECIALLY GIVEN
HINTS OF RELATIVELY DRY AIR BETWEEN H85-H7 ON MORNING SOUNDINGS AND
POTENTIAL FOR EVAPORATIVE COOLING.  BUT...AN ISOLD SUPERCELL /BRIEF
TORNADO/ CANNOT BE RULED OUT...ESPECIALLY AS THE STORMS INTERACT
WITH THE WRMFNT DRAPED EWD ACROSS NRN LA/WCNTRL MS OR WITH ANY CELLS
DEVELOPING AND/OR MERGING WITH THE LINE.

..RACY.. 07/30/2009

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

ATTN...WFO...JAN...LIX...LCH...SHV...HGX...

LAT...LON   32199429 32659305 32919151 32849082 32229055 31249058
            31019065 30589106 30609205 30559304 30669399 30889468
            31349436 32199429

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 30, 6:40 AM CDT	Mesoscale Discussion	SPC	Bossier, Caddo, De Soto, Red River, Webster	95 min
Jul 30, 2:02 PM CDT	Mesoscale Discussion	SPC	East Carroll, Franklin, Madison, Richland, Tensas, West Carroll	88 min
Jul 30, 3:42 PM CDT	Severe Thunderstorm Watch	SPC	Alcorn, Attala, Benton, Bolivar, Calhoun, Carroll and 37 more	3 hr
Jul 30, 4:10 PM CDT	Tornado Watch	SPC	Alcorn, Benton, Calhoun, Chickasaw, Coahoma, DeSoto and 16 more	6 hr
Jul 30, 5:01 PM CDT	Mesoscale Discussion	SPC	Alcorn, Attala, Benton, Calhoun, Carroll, Chickasaw and 34 more	59 min
Jul 30, 6:29 PM CDT	Mesoscale Discussion	SPC	Alcorn, Attala, Benton, Calhoun, Carroll, Chickasaw and 28 more	61 min
Jul 29, 8:42 PM CDT	Mesoscale Discussion	SPC	Armstrong, Bailey, Briscoe, Carson, Castro, Childress and 32 more	2 hr
Jul 29, 8:59 PM CDT	Severe Thunderstorm Watch	SPC	Archer, Baylor, Clay, Foard, Hardeman, Knox and 2 more	6 hr
Jul 29, 11:11 PM CDT	Mesoscale Discussion	SPC	Archer, Borden, Callahan, Clay, Coke, Collin and 33 more	2 hr
Jul 30, 12:52 AM CDT	Severe Thunderstorm Watch	SPC	Anderson, Bosque, Brown, Callahan, Coke, Coleman and 48 more	7 hr
Jul 30, 1:45 AM CDT	Mesoscale Discussion	SPC	Brown, Callahan, Coke, Coleman, Collin, Comanche and 30 more	90 min
Jul 30, 4:04 AM CDT	Mesoscale Discussion	SPC	Bosque, Brown, Coke, Coleman, Collin, Comanche and 21 more	86 min
Jul 30, 1:38 PM CDT	Mesoscale Discussion	SPC	Atascosa, Bandera, Bastrop, Bexar, Blanco, Caldwell and 16 more	67 min
Jul 30, 3:58 PM CDT	Mesoscale Discussion	SPC	Brewster, Culberson, Jeff Davis, Loving, Pecos, Presidio and 2 more	32 min

Nearby

Mesoscale Discussions in Louisiana, 2009 Mesoscale Discussions in Mississippi, 2009 Mesoscale Discussions in Texas, 2009 Every mesoscale discussion in 2009

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.