Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 73

January 26, 2012Mobile County, Washington County, Alabama; 18 parishes in Louisiana; 11 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Jan 26, 2012, 2:05 AM CST for Mobile County, Washington County, Alabama; 18 parishes in Louisiana; 11 counties in Mississippi. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Jan 26, 2012, 2:05 AM CST (08:05 UTC)
Expired: Jan 26, 2012, 4:30 AM CST
In force: 2 hr
Issued by: the Storm Prediction Center

All 31 counties

Mobile County, AL, Washington County, AL, Ascension Parish, LA, Assumption Parish, LA, Iberia Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Washington Parish, LA, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Lamar County, MS, Pearl River County, MS, Perry County, MS, Stone County, MS, Wayne County, MS

The watches that followed

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

Tornado Watch 17Jan 26, 4:20 AM CST

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 8.1 hours before the alert went out and 84 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: 794 J/kg
Mixed-layer CIN: -7 J/kg
Mixed-layer LCL: 544 m above ground
0-6 km bulk shear: 52 kt
0-1 km storm-relative helicity: 225 m²/s²
0-3 km storm-relative helicity: 235 m²/s²
Significant tornado parameter: 0.9
Supercell composite: 4.1

Open this sounding in Storm Lab

The text

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

278 
ACUS11 KWNS 260805
SWOMCD
SPC MCD 260805 
ALZ000-MSZ000-LAZ000-261030-

MESOSCALE DISCUSSION 0073
NWS STORM PREDICTION CENTER NORMAN OK
0205 AM CST THU JAN 26 2012

AREAS AFFECTED...PORTIONS SERN LA...SERN MS...SWRN AL.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 260805Z - 261030Z

THOUGH PRESENTLY IN RELATIVE INTENSITY LULL...REINTENSIFICATION OF
TSTM LINE IS POSSIBLE THROUGH REMAINDER PRE-DAWN HOURS ACROSS SERN
LA.  ACTIVITY WOULD POSE PRIMARY WIND DAMAGE THREAT AND
SECONDARY/CONDITIONAL TORNADO POTENTIAL...MAINLY ASSOCIATED WITH
BOW/LEWP MESOCIRCULATIONS...WHILE ADVANCING TOWARD MS/AL COAST. 
CONVECTIVE TRENDS WILL BE MONITORED ACCORDINGLY...AND WW MAY BE
REQUIRED IF SUSTAINED REORGANIZATION APPEARS IMMINENT AT MORE THAN
LOCAL/TRANSIENT SCALES.

AT 07Z...SFC MESOANALYSIS SHOWED SYNOPTIC COLD FRONT FROM SWRN AR
SWD ACROSS WRN LA THEN SSWWD OVER NWRN GULF. FRONT IS PRECEDED BY
NARROW BAND OF TSTMS JUST E OF MCB-BTR-PTN LINE THEN SSWWD OVER
GULF...PARALLEL TO FRONT.  IN MID-UPPER LEVELS...MOISTURE CHANNEL
IMAGERY INDICATES MID-UPPER CYCLONE OVER CENTRAL/S-CENTRAL
TX...DRIFTING NEWD TOWARD E TX AND ARKLATEX REGION.  SHORTWAVE
TROUGH ALSO IS EVIDENT PIVOTING EWD THROUGH SRN PORTION OF VORTEX
ALOFT.  MAIN PART OF ITS UVV FIELD IS EVIDENT IN
THICKENING/ELONGATING STRUCTURE OF HIGH CLOUDS FROM DEEP S TX NEWD
ACROSS E TX.  PERTURBATION SHOULD SHIFT NEWD ALONG TX COAST TO SWRN
LA...LEADING TO TIGHTENING OF LOW-MIDLEVEL HEIGHT GRADIENTS ON
MESO-ALPHA SCALE.  EXPECT RELATED STRONGER DEEP-LAYER SHEAR TO
SPREAD ACROSS COLD FRONT AND INTO PRE-CONVECTIVE WARM SECTOR BEFORE
12Z...IN STEP WITH INCREASING LARGE-SCALE UVV.  MORE FAVORABLE
ENVIRONMENT ALOFT MAY BE EVIDENT ALREADY WITH INCREASE IN
BKN/SCATTERED CONVECTION BETWEEN COLD FRONT AND PREFRONTAL
CONVERGENCE LINE OVER GULF.

IN SUPPORT OF DOMINANT LINEAR CONVECTIVE MODE...PRIMARY
CONVECTIVE/CONVERGENCE BOUNDARY REMAINS ALIGNED VERY NEARLY PARALLEL
TO MEAN WIND VECTOR INLAND...WHICH SHOULD REMAIN TRUE WITH APCH OF
BASAL SHORTWAVE TROUGH.  HOWEVER...ANY SUSTAINED TSTMS FORMING AHEAD
OF MAIN BAND STILL MAY ROTATE.  WARM-SECTOR ENVIRONMENT IS
CHARACTERIZED BY RICH LOW-LEVEL MOISTURE OVER COASTAL AREAS AND
GULF...SUPPORTING MLCAPE RANGING FROM AROUND 1000 J/KG OVER COASTAL
SERN LA...PER MODIFIED 06Z LIX RAOB...TO ABOUT 250 J/KG OVER SERN MS
AND SERN AL INLAND. EFFECTIVE SHEAR MAGNITUDES...NOW GENERALLY 40-50
KT...SHOULD INCREASE GRADUALLY TO 45-55 KT...BOTH  WITH TIME AND
FROM W-E.

..EDWARDS.. 01/26/2012

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

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

LAT...LON   29579204 29639195 30929072 31238962 31888825 31108771
            30288785 30218859 30178906 29948878 29548898 29418939
            29308924 29338913 29178899 28998915 29118922 28838943
            29078933 29088938 29198947 29228959 29318974 29239000
            29039021 29039048 29079056 29039079 29059099 29089086
            29199095 29309136 29419120 29549142 29479152 29619155
            29599170 29439179 29579204

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jan 26, 4:18 AM CST	Tornado Watch	SPC	Baldwin, Choctaw, Clarke, Conecuh, Escambia, Mobile and 3 more	7 hr
Jan 26, 7:29 AM CST	Mesoscale Discussion	SPC	Baldwin, Choctaw, Clarke, Conecuh, Escambia, Mobile and 3 more	91 min
Jan 26, 9:34 AM CST	Mesoscale Discussion	SPC	Autauga, Baldwin, Barbour, Bullock, Butler, Calhoun and 24 more	86 min
Jan 26, 9:55 AM CST	Tornado Watch	SPC	Autauga, Baldwin, Barbour, Bibb, Bullock, Butler and 34 more	7 hr
Jan 26, 2:16 PM CST	Mesoscale Discussion	SPC	Barbour, Dale, Henry, Houston, Lee, Russell	119 min
Jan 26, 5:35 PM CST	Mesoscale Discussion	SPC	Colbert, Fayette, Franklin, Lamar, Lauderdale, Lawrence and 5 more	55 min
Jan 25, 8:23 PM CST	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, East Feliciana, Iberia, Iberville and 16 more	97 min

Nearby

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