Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 2120

November 12, 2012Saint Tammany Parish, Washington Parish, Louisiana; Hancock County, Pearl River County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Nov 12, 2012, 3:42 AM CST for Saint Tammany Parish, Washington Parish, Louisiana; Hancock County, Pearl River County, Mississippi. It was in force for 63 min.

The area

The outline as issued.

The facts

Issued: Nov 12, 2012, 3:42 AM CST (09:42 UTC)
Expired: Nov 12, 2012, 4:45 AM CST
In force: 63 min
Issued by: the Storm Prediction Center
Chance of a watch: 5%

Counties Saint Tammany Parish, LA, Washington Parish, LA, Hancock County, MS, Pearl River County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 9.7 hours before the alert went out and 42 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: 32 J/kg
Mixed-layer CIN: -9 J/kg
Mixed-layer LCL: 888 m above ground
0-6 km bulk shear: 42 kt
0-1 km storm-relative helicity: 152 m²/s²
0-3 km storm-relative helicity: 184 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

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

742 
ACUS11 KWNS 120943
SWOMCD
SPC MCD 120942
MSZ000-LAZ000-121045-

MESOSCALE DISCUSSION 2120
NWS STORM PREDICTION CENTER NORMAN OK
0342 AM CST MON NOV 12 2012

AREAS AFFECTED...PARTS OF SERN LA AND FAR SRN MS

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 120942Z - 121045Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...RECENT INCREASE IN UPDRAFT INTENSITY HAS BEEN OBSERVED
OVER PARTS OF SERN LA.  THE PEAK IN STORM STRENGTH IS EXPECTED OVER
THE NEXT HR OR SO WITH WEAKENING EXPECTED THEREAFTER.  A WATCH WILL
NOT BE NEEDED.

DISCUSSION...SURFACE MESOANALYSIS SHOWS A MOISTURE AXIS EXTENDING
FROM S-CNTRL LA NNEWD INTO S-CNTRL MS.  A COLD FRONT IS PROGRESSING
SEWD FROM E-CNTRL MS INTO S-CNTRL LA AND WILL MOVE THROUGH THIS
REGION OVER THE NEXT SEVERAL HOURS.  A LOW LEVEL CONFLUENCE ZONE HAS
PREFERENTIALLY FAVORED A BROKEN BAND OF DEEP MOIST CONVECTION DURING
MOST OF THE NIGHT...WITH UPDRAFTS STRENGTHENING RECENTLY AND
RESULTING IN AN UPTICK IN LIGHTNING ACTIVITY FROM MAINLY I-10 NWD TO
THE LA/MS BORDER.  THE LAST HR WDSS-II 9 KM CAPPI AND ECHO TOP DATA
ARE COINCIDENT WITH THE TREND IN INTENSIFYING UPDRAFTS.  GIVEN THE
STRONG LOW LEVEL SHEAR PROFILE PER KLIX VWP AND DEEP MOIST BOUNDARY
LAYER CHARACTERIZED BY DEWPOINTS IN THE MID 60S...A ROGUE STRONG
WIND GUST CANNOT BE RULED OUT GIVEN MORE ORGANIZED NATURE OF
QUASI-BANDED CELLULAR ACTIVITY.  THE ENVIRONMENT WILL BECOME LESS
FAVORABLE FOR AN ISOLD WIND GUST AS STORMS 1) CONTINUE EWD AND
ENTRAIN PARCELS EMANATING FROM THE DRIER SERN U.S. SURFACE RIDGE AND
2) COLD FRONT UNDERCUTS ONGOING STORMS.

..SMITH/CORFIDI.. 11/12/2012

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

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

LAT...LON   30169066 31118988 31178934 30928906 30398938 30219035
            30169066

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Nov 11, 6:32 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Avoyelles, Bienville, Bossier, Caddo and 27 more	58 min

Nearby

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