Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 444

April 4, 201224 parishes in Louisiana; 8 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Apr 4, 2012, 2:29 AM CDT for 24 parishes in Louisiana; 8 counties in Texas. It was in force for 91 min.

The area

The outline as issued.

The facts

Issued: Apr 4, 2012, 2:29 AM CDT (07:29 UTC)
Expired: Apr 4, 2012, 4:00 AM CDT
In force: 91 min
Issued by: the Storm Prediction Center

All 32 counties

Acadia Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Jefferson Parish, LA, Lafayette Parish, LA, Lafourche Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Pointe Coupee Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Terrebonne Parish, LA, Vermilion Parish, LA, West Baton Rouge Parish, LA, Chambers County, TX, Hardin County, TX, Harris County, TX, Jefferson County, TX, Liberty County, TX, Orange County, TX, Polk County, TX, Tyler County, TX

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 7.5 hours before the alert went out and 176 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: 2379 J/kg
Mixed-layer CIN: -3 J/kg
Mixed-layer LCL: 1042 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: -5 m²/s²
0-3 km storm-relative helicity: 70 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.

856 
ACUS11 KWNS 040729
SWOMCD
SPC MCD 040729 
LAZ000-TXZ000-040900-

MESOSCALE DISCUSSION 0444
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CDT WED APR 04 2012

AREAS AFFECTED...PORTIONS SE TX...SRN LA.

CONCERNING...SEVERE THUNDERSTORM WATCH 138...

VALID 040729Z - 040900Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 138
CONTINUES.

CONTINUE VALID PORTIONS WWS UNTIL PASSAGE OF OUTFLOW BOUNDARIES AND
RELATED DEEP/STG CONVECTION.  WW 137 HAS BEEN EXTENDED LOCALLY UNTIL
8Z FOR AREAS NE HOU.  WW 138 MAY NEED SHORT EXTENSION OVER PORTIONS
SE TX FOR REMAINING NOTCH OF INFLOW AIR WITH FAVORABLE
BUOYANCY/SHEAR...AHEAD OF SMALL MULTICELL COMPLEX THAT WAS LOCATED
OVER PORTIONS MONTGOMERY/SAN JACINTO/POLK COUNTIES AT 7Z.  AREAS OF
WARM SECTOR NEAR COAST WILL BE MONITORED FOR ANY INCREASE IN SVR
POTENTIAL THAT MAY REQUIRE ANOTHER WW.  THREAT FOR WIND/HAIL
GENERALLY IS BECOMING MORE MRGL WITH TIME AND SWD EXTENT. 

SFC MESOANALYSIS AND REFLECTIVITY ANIMATIONS...AS OF 7Z...DEPICT
THREE PRIMARY/AGGREGATE OUTFLOW BOUNDARIES OVER REGION.  FIRST
TWO...AND NRN PORTION OF THIRD...HAVE PERSISTENT CONVECTION
CONTINUING TO REINFORCE THEIR MOVEMENT/BAROCLINICITY...
1. ESCAMBIA COUNTIES AL/FL...TO MOB BAY AND JUST OFFSHORE MS COAST
WWD ACROSS MSY AREA THEN ARCHING NWWD TO BTR...MOVING SWD ABOUT 5-10
KT MOST AREAS 
2. FROM W BTR...WSWWD ACROSS NRN PORTIONS JEFF DAVIS/CALCASIEU
PARISHES...THEN NWWD OVER TYLER COUNTY TX...MOVING SWD 10-15 KT.
3. LFK AREA SWWD ACROSS NWRN HARRIS...JACKSON AND REFUGIO
COUNTIES...MOVING SEWD 10-15 KT. 

S OF THESE BOUNDARIES...FCST SOUNDINGS INDICATE LITTLE OR NO MLCINH
WITH 1500-3000 J/KG MLCAPE...AMIDST 35-50 KT EFFECTIVE SHEAR
MAGNITUDES.  THESE PARAMETERS SUPPORT SVR POTENTIAL...ALTHOUGH MESSY
CONVECTIVE MODES AND ANAFRONTAL NATURE OF BOUNDARY/KINEMATIC
SITUATION ARE COUNTERBALANCING FACTORS. SOME POTENTIAL ALSO REMAINS
FOR TSTMS TO DEVELOP IN WARM SECTOR NEAR COAST.  SFC BOUNDARIES ARE
NEBULOUS AWAY FROM AFOREMENTIONED PROGRESSIVE OUTFLOWS. 
HOWEVER...STREAMLINE ANALYSIS OF 850-MB FLOW...BASED ON OBSERVED
VWP/PROFILER DATA OVERLAID WITH GAP-FILLING RUC NOWCAST
WINDS...INDICATES BROAD CONFLUENCE ZONE OVER SWRN LA CORRESPONDING
TO THAT REGION WHERE CONVECTION HAS BEEN DEVELOPING GRADUALLY...THEN
INTENSIFYING WHILE MOVING NWD.  GIVEN SWD/COASTWARD PROGRESS OF
OUTFLOW BOUNDARIES...GESTATION ZONE FOR WARM-SECTOR CONVECTION IS
GETTING EVER NARROWER.  THIS TREND WILL LEAD TO LESS TIME FOR CELLS
THAT CAN DEVELOP TO MATURE BEFORE INTERACTING WITH--AND BEING
UNDERCUT BY--OUTFLOW BOUNDARIES.

..EDWARDS.. 04/04/2012

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

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

LAT...LON   29339471 29829570 31149467 30679406 30589301 30879158
            30409104 30169015 30118922 29898925 29758936 29658956
            29608972 29468954 29388937 29328921 29208909 29208899
            28968913 29128923 28918938 29088933 29118942 29228944
            29308988 29079017 29039038 29089051 29059063 29039089
            29069095 29189093 29259126 29329137 29429146 29419125
            29519137 29539152 29539154 29639159 29649164 29549171
            29489180 29589208 29519226 29599267 29779323 29749374
            29659386 29699398 29509448 29449462 29339471

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 3, 8:47 PM CDT	Mesoscale Discussion	SPC	Bienville, Bossier, Caddo, Claiborne, De Soto, Lincoln and 4 more	58 min
Apr 3, 9:48 PM CDT	Severe Thunderstorm Watch	SPC	Acadia, Allen, Avoyelles, Beauregard, Bienville, Calcasieu and 23 more	8 hr
Apr 3, 11:24 PM CDT	Mesoscale Discussion	SPC	Allen, Avoyelles, East Baton Rouge, East Feliciana, Evangeline, Grant and 12 more	96 min
Apr 3, 7:35 PM CDT	Severe Thunderstorm Watch	SPC	Austin, Bastrop, Brazos, Burleson, Colorado, Fayette and 13 more	7 hr
Apr 4, 12:19 PM CDT	Mesoscale Discussion	SPC	Aransas, Austin, Bee, Brazoria, Calhoun, Chambers and 25 more	86 min
Apr 4, 12:55 PM CDT	Severe Thunderstorm Watch	SPC	Aransas, Bee, Brazoria, Brooks, Calhoun, Cameron and 19 more	6 hr
Apr 4, 3:32 PM CDT	Mesoscale Discussion	SPC	Aransas, Brazoria, Calhoun, Galveston, Kleberg, Matagorda and 1 more	88 min

Nearby

Mesoscale Discussions in Louisiana, 2012 Mesoscale Discussions in Texas, 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.