Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 1843

August 31, 201212 parishes in Louisiana; Orange County, Texas

The Storm Prediction Center issued this mesoscale discussion at Aug 31, 2012, 4:14 AM CDT for 12 parishes in Louisiana; Orange County, Texas. It was in force for 91 min.

The area

The outline as issued.

The facts

Issued: Aug 31, 2012, 4:14 AM CDT (09:14 UTC)
Expired: Aug 31, 2012, 5:45 AM CDT
In force: 91 min
Issued by: the Storm Prediction Center
Chance of a watch: 5%

Counties Allen Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Calcasieu Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Evangeline Parish, LA, Grant Parish, LA, Jefferson Davis Parish, LA, LaSalle Parish, LA, Rapides Parish, LA, Vernon Parish, LA, Orange County, TX

The nearest sounding before it

Lake Charles Mun, LA (KLCH), launched 00:00Z, 9.2 hours before the alert went out and 93 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: 371 J/kg
Mixed-layer CIN: -20 J/kg
Mixed-layer LCL: 953 m above ground
0-6 km bulk shear: 21 kt
0-1 km storm-relative helicity: 22 m²/s²
0-3 km storm-relative helicity: 46 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.

485 
ACUS11 KWNS 310914
SWOMCD
SPC MCD 310914 
LAZ000-TXZ000-311045-

MESOSCALE DISCUSSION 1843
NWS STORM PREDICTION CENTER NORMAN OK
0414 AM CDT FRI AUG 31 2012

AREAS AFFECTED...LA AND PARTS OF SRN AR...WRN MS

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 310914Z - 311045Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...VIGOROUS ONGOING STORM DEVELOPMENT ACROSS SOUTHWEST
THROUGH CENTRAL LOUISIANA MAY PERSIST ANOTHER COUPLE OF
HOURS...BEFORE BEGINNING TO DIMINISH BY 11-13Z.  SEVERE
WIND/ISOLATED TORNADO POTENTIAL APPEARS LOW...BUT MAY NOT BE
COMPLETELY NEGLIGIBLE.

DISCUSSION...A RELATIVELY DEEP LAYER...NEAR SURFACE CONFLUENCE ZONE
TO THE SOUTH OF THE REMNANTS OF ISAAC HAS BEEN THE FOCUS FOR THE
MOST VIGOROUS CONVECTIVE DEVELOPMENT DURING THE PAST FEW HOURS. 
ACTIVITY HAS BEEN SUPPORTED BY INFLOW OF MOISTURE CHARACTERIZED BY
MID/UPPER 70S SURFACE DEW POINTS...WHICH MAY BE CONTRIBUTING TO AT
LEAST MODEST CAPE.  BENEATH THE MID/UPPER DRY SLOT TO THE SOUTH OF
THE CIRCULATION CENTER OF ISAAC...NOW OVER WEST CENTRAL
ARKANSAS...THERMODYNAMIC PROFILES HAVE BEEN CONDUCIVE TO
THUNDERSTORM ACTIVITY WITH OCCASIONALLY FREQUENT CLOUD TO GROUND
LIGHTNING STRIKES...IN ADDITION TO LOCALLY VERY HEAVY RAINFALL...
LIKELY AT RATES WELL IN EXCESS OF 2 INCHES PER HOUR.  AS THE SURFACE
LOW CENTER ASSOCIATED WITH THE REMNANTS OF ISAAC CONTINUES TO SLOWLY
DEVELOP NORTHWARD TOWARD THE FAYETTEVILLE/ HARRISON AREA...AND
GRADUALLY WEAKEN...THROUGH 11-13Z...WEAKENING WIND FIELDS AND
LOW-LEVEL CONVERGENCE ACROSS SOUTHWEST THROUGH CENTRAL LOUISIANA MAY
RESULT IN DIMINISHING CONVECTIVE TRENDS.

..KERR/THOMPSON.. 08/31/2012

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

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

LAT...LON   30749372 31569290 32129213 31829145 30879200 30029314
            30099392 30479393 30749372

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 30, 9:05 PM CDT	Mesoscale Discussion	SPC	Washington	55 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.