Alert archive / Louisiana / Mesoscale Discussions in 2011

Mesoscale Discussion 211

March 9, 201115 parishes in Louisiana; 9 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Mar 9, 2011, 4:39 AM CST for 15 parishes in Louisiana; 9 counties in Mississippi. It was in force for 66 min.

The area

The outline as issued.

The facts

Issued: Mar 9, 2011, 4:39 AM CST (10:39 UTC)
Expired: Mar 9, 2011, 5:45 AM CST
In force: 66 min
Issued by: the Storm Prediction Center

All 24 counties

Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, Iberville Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Lamar County, MS, Pearl River County, MS, Perry County, MS, Stone County, MS

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Tornado Watch 46Mar 9, 7:25 AM CST

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 10.7 hours before the alert went out and 56 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: 841 J/kg
Mixed-layer CIN: -30 J/kg
Mixed-layer LCL: 473 m above ground
0-6 km bulk shear: 57 kt
0-1 km storm-relative helicity: 652 m²/s²
0-3 km storm-relative helicity: 774 m²/s²
Significant tornado parameter: 4.0
Supercell composite: 24.8

Open this sounding in Storm Lab

The text

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

583 
ACUS11 KWNS 091039
SWOMCD
SPC MCD 091039 
MSZ000-LAZ000-091145-

MESOSCALE DISCUSSION 0211
NWS STORM PREDICTION CENTER NORMAN OK
0439 AM CST WED MAR 09 2011

AREAS AFFECTED...SERN LA/SERN MS

CONCERNING...TORNADO WATCH 45...

VALID 091039Z - 091145Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 45 CONTINUES.

THE THREAT FOR TORNADO-PRODUCING SUPERCELLS IS INCREASING ACROSS
PORTIONS OF SERN LA AND SERN MS. TORNADO WATCH 45 HAS BEEN EXPANDED
SWD TO INCLUDE THE REMAINDER OF SERN LA.

A SQUALL LINE EXTENDING FROM NEAR MEI TO 30 MILES WEST OF PIB TO 35
MILES SSW OF HEZ CONTINUES ADVANCING E-SEWD WITH AN ATTENDANT THREAT
FOR DAMAGING WINDS AND ISOLATED TORNADOES. MEANWHILE...RECENT RADAR
IMAGERY HAS INDICATED AN UPWARD TREND IN SEMI-DISCRETE CONVECTION
OVER SERN LA AND SERN MS AHEAD OF THE SQUALL LINE. THIS ACTIVITY IS
IN RESPONSE TO INCREASING ASCENT IN ASSOCIATION WITH A SUBTLE
MID-LEVEL SHORTWAVE TROUGH SWINGING THROUGH THE NWRN GULF OF MEXICO
AND SRN LA. THE ASCENT IS BEING AUGMENTED BY INCREASING LOW-LEVEL
CONVERGENCE WITHIN THE EXIT REGION OF A 50-55-KT 850-MB JET NOSING
INTO SRN LA PER RUC ANALYSIS. AS SUCH...SEMI-DISCRETE CONVECTION IS
FORECAST TO CONTINUE TO EVOLVE OVER SERN LA AND STREAM NEWD INTO
SERN MS EARLY THIS MORNING. RUC ANALYSIS INDICATES SBCAPE VALUES ON
THE ORDER OF 500-1000 J/KG OVER THE DISCUSSION AREA...WITH LITTLE IN
THE WAY OF CONVECTIVE INHIBITION...ALLOWING CONVECTION TO BECOME
ROOTED IN THE BOUNDARY LAYER AND DEEPEN. EFFECTIVE BULK SHEAR
MAGNITUDES AROUND 50 KT WILL PROMOTE SUPERCELLULAR STRUCTURES. GIVEN
VERY HIGH EFFECTIVE STORM-RELATIVE HELICITY VALUES BETWEEN 500 TO
700 M2/S2...LOW-LEVEL ROTATION WILL BE A THREAT WITH ANY SUSTAINED
SUPERCELLS /AS EVIDENT WITH THE EVOLVING SUPERCELL OVER CNTRL LAKE
PONTCHARTRAIN AND MARION COUNTY MISSISSIPPI/ WITH AN ATTENDANT
THREAT FOR TORNADOES. TORNADO WATCH 45 HAS BEEN EXPANDED SWD ACROSS
SERN LA IN COORDINATION WITH WFO SLIDELL.

..COHEN.. 03/09/2011

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

ATTN...WFO...MOB...JAN...LIX...LCH...

LAT...LON   29949193 30569167 30959042 31538916 31338860 30698860
            30218904 29619032 29949193

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Mar 8, 6:27 PM CST	Mesoscale Discussion	SPC	Bienville, Bossier, Caddo, Claiborne, Jackson, Lincoln and 4 more	63 min
Mar 8, 7:37 PM CST	Tornado Watch	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, Beauregard and 51 more	7 hr
Mar 8, 9:40 PM CST	Mesoscale Discussion	SPC	Avoyelles, Bienville, Caldwell, Catahoula, Claiborne, Concordia and 32 more	65 min
Mar 9, 1:28 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, Beauregard and 47 more	92 min
Mar 9, 2:39 AM CST	Tornado Watch	SPC	Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 16 more	5 hr
Mar 9, 6:28 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, Beauregard and 47 more	92 min
Mar 9, 7:26 AM CST	Tornado Watch	SPC	Plaquemines, Saint Bernard	6 hr
Mar 9, 9:31 AM CST	Mesoscale Discussion	SPC	Plaquemines, Saint Bernard	59 min

Nearby

Mesoscale Discussions in Louisiana, 2011 Mesoscale Discussions in Mississippi, 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.