Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 314

March 21, 201225 parishes in Louisiana; Adams County, Amite County, Wilkinson County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Mar 21, 2012, 4:38 AM CDT for 25 parishes in Louisiana; Adams County, Amite County, Wilkinson County, Mississippi. It was in force for 97 min.

The area

The outline as issued.

The facts

Issued
Mar 21, 2012, 4:38 AM CDT (09:38 UTC)
Expired
Mar 21, 2012, 6:15 AM CDT
In force
97 min
Issued by
the Storm Prediction Center
All 28 counties

Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Lafayette Parish, LA, Lafourche Parish, LA, LaSalle Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Wilkinson County, MS

The watches that followed

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

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 9.6 hours before the alert went out and 178 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, Slidell Radar S, LA at 00:00Z on 2012-03-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1474 joules per kilogram.LCLEL10008507005003002001001 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, Slidell Radar S, LA at 00:00Z on 2012-03-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 151 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
1474 J/kg
Mixed-layer CIN
0 J/kg
Mixed-layer LCL
578 m above ground
0-6 km bulk shear
30 kt
0-1 km storm-relative helicity
151 m²/s²
0-3 km storm-relative helicity
239 m²/s²
Significant tornado parameter
1.2
Supercell composite
8.0

Open this sounding in Storm Lab

The text

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

483 
ACUS11 KWNS 210938
SWOMCD
SPC MCD 210938 
LAZ000-MSZ000-211115-

MESOSCALE DISCUSSION 0314
NWS STORM PREDICTION CENTER NORMAN OK
0438 AM CDT WED MAR 21 2012

AREAS AFFECTED...PARTS OF S CNTRL THRU NE LOUISIANA AND SW
MISSISSIPPI

CONCERNING...TORNADO WATCH 95...

VALID 210938Z - 211115Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 95 CONTINUES.

A NEW WW PROBABLY WILL BE ISSUED ACROSS PARTS OF EASTERN LOUISIANA
AND SOUTHWEST MISSISSIPPI BY 11Z.

A MESO LOW HAS BECOME MORE READILY EVIDENT IN SURFACE ANALYSES THE
PAST FEW HOURS...ALONG THE CONGLOMERATE CONVECTIVE OUTFLOW BOUNDARY
NEAR SOUTH CENTRAL LOUISIANA COASTAL AREAS TO THE SOUTHWEST OF
LAFAYETTE.  THE LONGEVITY OF THIS FEATURE REMAINS UNCLEAR FROM MODEL
DATA...BUT NAM GUIDANCE APPEARS TO SUGGEST THAT THE WEAK LOW MAY
SLOWLY MIGRATE INLAND ACROSS SOUTHEASTERN LOUISIANA...TOWARD THE
LAKE PONTCHARTRAIN/NEW ORLEANS AREA BETWEEN NOW AND 15-18Z.  THIS
COULD BECOME THE PRIMARY FOCUS FOR FURTHER SUPERCELLULAR TYPE
DEVELOPMENT AND UPSCALE CONVECTIVE GROWTH...AIDED BY MODEST INFLOW
OF RICH BOUNDARY LAYER MOISTURE /70F+ SURFACE DEW POINTS/ OFF THE
GULF OF MEXICO.  IN ADDITION TO THE CONTINUING RISK FOR ISOLATED
TORNADOES AND HEAVY RAINFALL...A SOMEWHAT BROADER SCALE POTENTIALLY
DAMAGING WIND GUST THREAT COULD ALSO EVENTUALLY EVOLVE.

..KERR.. 03/21/2012

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

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

LAT...LON   29469212 30289223 30819238 31669227 32209183 31619106
            30709011 29589011 29089113 29219170 29469212

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Mar 20, 8:02 PM CDTTornado WatchSPCBeauregard, Calcasieu, Cameron, Vernon4 hr
Mar 20, 10:23 PM CDTMesoscale DiscussionSPCAllen, Beauregard, Calcasieu, Jefferson Davis, Natchitoches, Vernon67 min
Mar 20, 10:59 PM CDTTornado WatchSPCAcadia, Allen, Beauregard, Bienville, Calcasieu, Caldwell and 17 more7 hr
Mar 21, 2:17 AM CDTMesoscale DiscussionSPCAcadia, Avoyelles, Caldwell, Catahoula, Concordia, Evangeline and 17 more118 min
Mar 21, 5:04 AM CDTTornado WatchSPCAcadia, Ascension, Assumption, Avoyelles, Caldwell, Catahoula and 33 more7 hr
Mar 21, 7:48 AM CDTMesoscale DiscussionSPCAscension, Assumption, Avoyelles, East Baton Rouge, East Feliciana, Iberville and 10 more87 min
Mar 21, 9:25 AM CDTMesoscale DiscussionSPCAscension, Concordia, East Baton Rouge, East Carroll, East Feliciana, Franklin and 17 more95 min
Mar 21, 10:07 AM CDTTornado WatchSPCAscension, East Carroll, East Feliciana, Franklin, Jefferson, Lafourche and 17 more8 hr
Mar 21, 12:19 PM CDTMesoscale DiscussionSPCJefferson, Lafourche, Orleans, Plaquemines, Saint Bernard, Saint Tammany and 1 more86 min
Mar 21, 3:47 PM CDTMesoscale DiscussionSPCSaint Bernard88 min
Mar 21, 5:40 PM CDTMesoscale DiscussionSPCOrleans, Plaquemines, Saint Bernard35 min
Mar 21, 6:02 PM CDTTornado WatchSPCPlaquemines, Saint Bernard9 hr

Nearby

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