Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 1785

August 18, 20124 parishes in Louisiana; 4 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2012, 10:56 AM CDT for 4 parishes in Louisiana; 4 counties in Mississippi. It was in force for 94 min.

The area

The outline as issued.

The facts

Issued: Aug 18, 2012, 10:56 AM CDT (15:56 UTC)
Expired: Aug 18, 2012, 12:30 PM CDT
In force: 94 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

Counties East Carroll Parish, LA, Madison Parish, LA, Richland Parish, LA, West Carroll Parish, LA, Hinds County, MS, Issaquena County, MS, Sharkey County, MS, Warren County, MS

The radar

The Jackson/Brandon,MS radar (KDGX), 111 km from the middle of the area, began a volume at 15:57 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Jackson, MS (KJAN), launched 12:00Z, 3.9 hours before the alert went out and 101 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: 1913 J/kg
Mixed-layer CIN: -49 J/kg
Mixed-layer LCL: 828 m above ground
0-6 km bulk shear: 19 kt
0-1 km storm-relative helicity: 52 m²/s²
0-3 km storm-relative helicity: 42 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.2

Open this sounding in Storm Lab

The text

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

491 
ACUS11 KWNS 181556
SWOMCD
SPC MCD 181556 
MSZ000-LAZ000-181730-

MESOSCALE DISCUSSION 1785
NWS STORM PREDICTION CENTER NORMAN OK
1056 AM CDT SAT AUG 18 2012

AREAS AFFECTED...PARTS OF NERN LA INTO W CNTRL MS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 181556Z - 181730Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...SEVERE WEATHER POTENTIAL STILL APPEARS RELATIVELY LOW IN
THE NEAR TERM...BUT MAY SLOWLY INCREASE THROUGH THE EARLY AFTERNOON
HOURS ACROSS PARTS OF NORTHEASTERN LOUISIANA INTO CENTRAL
MISSISSIPPI.  IT IS NOT CERTAIN THAT A WW WILL BE NEEDED...BUT
TRENDS ARE BEING MONITORED.

DISCUSSION...THUNDERSTORMS HAVE RECENTLY FORMED AND INTENSIFIED
WITHIN A NORTH-SOUTH BAND...ROUGHLY ALONG A LINE FROM EAST OF EL
DORADO AR SOUTHWARD INTO AREAS EAST OF NATCHITOCHES LA.  THIS IS
GENERALLY WELL SOUTH OF THE STRONGER WESTERLIES...WITHIN CONVECTIVE
LAYER MEAN FLOW THAT APPEARS GENERALLY ON THE ORDER OF 10-15 KTS OR
LESS.  THERMODYNAMIC PROFILES ARE CHARACTERIZED BY MODEST LAPSE
RATES...AT BEST...BUT HIGH MOISTURE CONTENT /UP TO AROUND 2 INCHES/
IS CONTRIBUTING TO SIZABLE CAPE SUPPORTIVE OF INTENSE UPDRAFTS WITH
HEAVY RAIN AND HAIL.  GIVEN THE RELATIVELY WARM PROFILES...SEVERE
HAIL REACHING THE SURFACE APPEARS LOW.  HOWEVER ...HEAVY
PRECIPITATION LOADING COULD CONTRIBUTE TO DOWNBURSTS WITH LOCALIZED
STRONG SURFACE GUSTS.  THROUGH 17-19Z...THIS POTENTIAL APPEARS
HIGHEST WHERE LOW-LEVEL CONVERGENCE WILL BE ENHANCED NEAR THE
INTERSECTION OF THE EASTWARD ADVANCING CONVECTIVE LINE AND A
LINGERING EAST-WEST FRONTAL ZONE...EAST OF MONROE LA INTO THE
JACKSON MS AREA.

..KERR/MEAD.. 08/18/2012

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

ATTN...WFO...JAN...

LAT...LON   32929171 32969123 32859051 32359008 32139045 32219136
            32329186 32929171

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 17, 7:53 PM CDT	Mesoscale Discussion	SPC	Claiborne, East Carroll, Morehouse, Union, West Carroll	2 hr
Aug 18, 6:29 AM CDT	Mesoscale Discussion	SPC	Claiborne, East Carroll, Lincoln, Morehouse, Union, Webster and 1 more	2 hr

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; radar from the NEXRAD Level II archive.