Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 243

March 11, 20128 counties in Arkansas; 18 parishes in Louisiana; 11 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Mar 11, 2012, 5:36 PM CDT for 8 counties in Arkansas; 18 parishes in Louisiana; 11 counties in Mississippi. It was in force for 84 min.

The area

The outline as issued.

The facts

Issued: Mar 11, 2012, 5:36 PM CDT (22:36 UTC)
Expired: Mar 11, 2012, 7:00 PM CDT
In force: 84 min
Issued by: the Storm Prediction Center

All 37 counties

Arkansas County, AR, Ashley County, AR, Bradley County, AR, Chicot County, AR, Desha County, AR, Drew County, AR, Lincoln County, AR, Phillips County, AR, Avoyelles Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Richland Parish, LA, Tensas Parish, LA, Union Parish, LA, West Carroll Parish, LA, Winn Parish, LA, Bolivar County, MS, Coahoma County, MS, Humphreys County, MS, Issaquena County, MS, Leflore County, MS, Quitman County, MS, Sharkey County, MS, Sunflower County, MS, Tallahatchie County, MS, Warren County, MS, Washington County, MS

The radar

The Jackson/Brandon,MS radar (KDGX), 166 km from the middle of the area, began a volume at 22:37 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.

Tornado Watch 72Mar 11, 6:45 PM CDT

The nearest sounding before it

Jackson, MS (KJAN), launched 12:00Z, 10.6 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 960 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 201 m²/s²
0-3 km storm-relative helicity: 235 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.

404 
ACUS11 KWNS 112236
SWOMCD
SPC MCD 112236 
MSZ000-ARZ000-LAZ000-120000-

MESOSCALE DISCUSSION 0243
NWS STORM PREDICTION CENTER NORMAN OK
0536 PM CDT SUN MAR 11 2012

AREAS AFFECTED...CNTRL/NE LOUISIANA...SE AR...WRN MS

CONCERNING...TORNADO WATCH 71...

VALID 112236Z - 120000Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 71 CONTINUES.

A NEW WW LIKELY WILL BE NEEDED BY THE CURRENT 00Z EXPIRATION OF WW
71.

WITHIN A BROADER SOUTHERLY LOW-LEVEL JET ACROSS THE WESTERN GULF
COAST/LOWER MISSISSIPPI VALLEY REGION...LATEST RUC GUIDANCE
INDICATES THAT A 50+ KT 850 MB JET CORE IS IN THE PROCESS OF NOSING
OUT OF SOUTHEAST TEXAS THROUGH PARTS OF CENTRAL/NORTHEAST LOUISIANA.
ENHANCED FORCING FOR UPWARD VERTICAL MOTION AND LOW-LEVEL SHEAR
ASSOCIATED WITH THIS FEATURE APPEAR TO BE CONTRIBUTING TO THE MOST
VIGOROUS CONVECTIVE DEVELOPMENT. THIS APPEARS LIKELY TO REMAIN THE
CASE INTO THE EVENING HOURS AS IT CONTINUES NORTHEASTWARD THROUGH
THE LOWER MISSISSIPPI VALLEY.

ORGANIZED IN A BROKEN LINE...STRONGEST STORMS ARE CURRENTLY EMBEDDED
WITHIN A BROADER BAND OF PRECIPITATION...WHERE WEAK LAPSE RATES ARE
SUPPORTING ONLY VERY WEAK BOUNDARY LAYER BASED CAPE. 
BUT...HODOGRAPHS ARE LARGE AND CLOCKWISE CURVED...IN THE PRESENCE OF
A NEAR SATURATED LOW-LEVEL ENVIRONMENT CHARACTERIZED BY SEASONABLY
HIGH MOISTURE CONTENT.  THE RISK FOR TORNADOES CANNOT BE RULED
OUT...BUT WITH THE ADDITIONAL LIMITING FACTOR OF RELATIVELY WEAK
HIGH-LEVEL FLOW/SHEAR...DAMAGING CONVECTIVELY ENHANCED SURFACE GUSTS
MAY BE THE PRIMARY THREAT AS STORMS SPREAD TOWARD THE MISSISSIPPI
DELTA REGION AND ADJACENT SOUTHEAST ARKANSAS BETWEEN NOW AND 01-02Z.

..KERR.. 03/11/2012

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

ATTN...WFO...MEG...JAN...LZK...LCH...SHV...

LAT...LON   32289282 34279182 34559102 34148992 32549050 30999179
            30929264 32289282

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Mar 11, 6:42 PM CDT	Tornado Watch	SPC	Ashley, Chicot	8 hr
Mar 11, 11:31 AM CDT	Mesoscale Discussion	SPC	Bossier, Caddo, De Soto, Red River, Sabine	89 min
Mar 11, 11:55 AM CDT	Tornado Watch	SPC	Allen, Beauregard, Bienville, Bossier, Caddo, Calcasieu and 18 more	7 hr
Mar 11, 2:47 PM CDT	Mesoscale Discussion	SPC	Allen, Beauregard, Bienville, Calcasieu, De Soto, Grant and 10 more	118 min

Nearby

Mesoscale Discussions in Louisiana, 2012 Mesoscale Discussions in Mississippi, 2012 Mesoscale Discussions in Arkansas, 2012 Every 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.