Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 2147

December 10, 201229 parishes in Louisiana; 25 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Dec 10, 2012, 4:07 AM CST for 29 parishes in Louisiana; 25 counties in Mississippi. It was in force for 113 min.

The area

The outline as issued.

The facts

Issued
Dec 10, 2012, 4:07 AM CST (10:07 UTC)
Expired
Dec 10, 2012, 6:00 AM CST
In force
113 min
Issued by
the Storm Prediction Center
Chance of a watch
40%
All 54 counties

Acadia Parish, LA, Allen Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, Cameron Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Vermilion Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Claiborne County, MS, Copiah County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, Hinds County, MS, Jasper County, MS, Jefferson County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Newton County, MS, Pearl River County, MS, Pike County, MS, Rankin County, MS, Scott County, MS, Simpson County, MS, Smith County, MS, Walthall County, MS, Wilkinson County, MS

The watches that followed

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

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 10.1 hours before the alert went out and 155 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-pSkew-T log-p diagram, Slidell Radar S, LA at 00:00Z on 2012-12-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 622 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Slidell Radar S, LA at 00:00Z on 2012-12-10The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 188 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
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
622 J/kg
Mixed-layer CIN
-3 J/kg
Mixed-layer LCL
645 m above ground
0-6 km bulk shear
50 kt
0-1 km storm-relative helicity
188 m²/s²
0-3 km storm-relative helicity
151 m²/s²
Significant tornado parameter
0.6
Supercell composite
4.4

Open this sounding in Storm Lab

The text

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

448 
ACUS11 KWNS 101007
SWOMCD
SPC MCD 101007 
MSZ000-LAZ000-TXZ000-101200-

MESOSCALE DISCUSSION 2147
NWS STORM PREDICTION CENTER NORMAN OK
0407 AM CST MON DEC 10 2012

AREAS AFFECTED...SRN LA INTO SRN MN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 101007Z - 101200Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...THUNDERSTORMS WILL CONTINUE TO AFFECT THE AREA THIS
MORNING...WITH LOCALLY STRONG TO SEVERE WIND GUSTS POSSIBLE. A
BRIEF/WEAK TORNADO COULD ALSO OCCUR.

DISCUSSION...A LINE OF THUNDERSTORMS LOCATED ALONG THE COLD FRONT
CONTINUES TO SHIFT EWD ACROSS LA AND INTO WRN MS. AREA WIND
PROFILERS SHOW STRONG FLOW ORIENTED PARALLEL TO THE FRONT...AND
RADAR SHOWS SOME TENDENCY FOR BOWING STRUCTURES. WITH UPPER 60S F
DEWPOINTS AHEAD OF THE LINE...INSTABILITY IS SUFFICIENT FOR
CONTINUED STRONG STORMS...AND ISOLATED SEVERE WIND GUSTS MAY OCCUR.

AHEAD OF THE LINE...SURFACE ANALYSIS INDICATES RELATIVELY HIGHER
PRESSURE FALLS WHERE UNSTABLE AIR IS MOVING NWD. SCATTERED
THUNDERSTORMS ARE ALSO FORMING AHEAD OF THE FRONT...AND THESE COULD
POSE AN ISOLATED/WEAK TORNADO THREAT BEFORE MERGING WITH THE FRONT.
LOW LEVEL SHEAR IS NOT PARTICULARLY STRONG...BUT SUFFICIENT FOR
STORMS TO ACQUIRE ROTATION.

..JEWELL/THOMPSON.. 12/10/2012

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

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

LAT...LON   29679387 30879264 32109113 32439043 32488944 32398894
            32078875 31508874 30168994 29159133 29429241 29649330
            29679387

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Dec 9, 8:38 PM CSTMesoscale DiscussionSPCBeauregard, Bienville, Bossier, Caddo, Caldwell, Claiborne and 15 more67 min
Dec 9, 9:59 PM CSTMesoscale DiscussionSPCConcordia, East Carroll, Franklin, Madison, Tensas61 min
Dec 9, 11:24 PM CSTMesoscale DiscussionSPCCaldwell, Catahoula, East Carroll, Franklin, Grant, LaSalle and 6 more66 min
Dec 10, 5:44 AM CSTTornado WatchSPCAscension, Assumption, East Baton Rouge, East Feliciana, Iberia, Iberville and 10 more5 hr
Dec 10, 7:31 AM CSTMesoscale DiscussionSPCAscension, Assumption, Iberia, Jefferson, Lafourche, Livingston and 11 more119 min
Dec 10, 8:51 AM CSTTornado WatchSPCJefferson, Orleans, Plaquemines, Saint Bernard, Saint Charles, Saint John the Baptist and 1 more6 hr
Dec 10, 10:24 AM CSTMesoscale DiscussionSPCOrleans2 hr

Nearby

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