Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 2007

September 30, 201219 parishes in Louisiana; 16 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Sep 30, 2012, 10:33 AM CDT for 19 parishes in Louisiana; 16 counties in Mississippi. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: Sep 30, 2012, 10:33 AM CDT (15:33 UTC)
Expired: Sep 30, 2012, 12:30 PM CDT
In force: 117 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 35 counties

Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberville Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Orleans 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 Martin Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Amite County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, Hancock County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Pearl River County, MS, Pike County, MS, Stone County, MS, Walthall County, MS, Wilkinson County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 3.6 hours before the alert went out and 97 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: 1360 J/kg
Mixed-layer CIN: -3 J/kg
Mixed-layer LCL: 552 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: 105 m²/s²
0-3 km storm-relative helicity: 178 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 2.9

Open this sounding in Storm Lab

The text

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

102 
ACUS11 KWNS 301533
SWOMCD
SPC MCD 301533 
MSZ000-LAZ000-301730-

MESOSCALE DISCUSSION 2007
NWS STORM PREDICTION CENTER NORMAN OK
1033 AM CDT SUN SEP 30 2012

AREAS AFFECTED...SERN LA THROUGH SRN MS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 301533Z - 301730Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...A FEW STORMS MIGHT BECOME CAPABLE OF ISOLATED DAMAGING
WIND GUSTS AND PERHAPS A COUPLE OF BRIEF TORNADOES FROM SERN LA
THROUGH SRN MS THIS AFTERNOON. AREA WILL CONTINUE TO BE
MONITORED...BUT ANY WW ISSUANCE WILL ULTIMATELY DEPEND ON CONVECTIVE
TRENDS AND ORGANIZATION.

DISCUSSION...A WARM FRONT EXTENDS FROM A SURFACE LOW IN WCNTRL LA
THROUGH SRN MS WHILE A PREFRONTAL TROUGH EXTENDS SWD FROM THE LOW
THROUGH SWRN LA. RICH GULF MOISTURE WITH LOW 70S DEWPOINTS HAS
SPREAD INLAND THROUGH WARM SECTOR...BUT INSTABILITY REMAINS MODEST
DUE TO WIDESPREAD CLOUDS AND WEAK MID LEVEL LAPSE RATES. PARTIAL
CLEARING EVIDENT ON VISIBLE IMAGERY IS SPREADING INTO SERN LA...AND
THIS SHOULD HELP BOOST MLCAPE TO 1500-2000 J/KG THIS AFTERNOON WHERE
SOME INCREASE IN INTENSITIES MIGHT OCCUR. LARGER 0-2 KM HODOGRAPHS
SHOULD REMAIN NORTH OF THE WARM FRONT WHERE INSTABILITY WILL BE MORE
LIMITED. HOWEVER...A SLY LLJ WILL SHIFT SLOWLY EWD THROUGH THE WARM
SECTOR IN ASSOCIATION WITH A VERY SLOW MOVING UPPER TROUGH. WHILE
SHEAR THROUGH A DEEPER LAYER IS EXPECTED TO REMAIN AOB 35 KT THIS
AFTERNOON...SUFFICIENT LOW LEVEL SHEAR WILL EXIST ALONG LLJ AXIS TO
MAINTAIN A THREAT FOR AT LEAST TRANSIENT UPDRAFT ROTATION AS WELL AS
LEWP/BOWING SEGMENTS. ANY TORNADO THREAT MAY BE SLIGHTLY HIGHER IN
SRN MS WHERE STORMS WILL HAVE POTENTIAL TO INTERACT WITH THE WARM
FRONT.

..DIAL/HART.. 09/30/2012

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

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

LAT...LON   30059225 31749094 31638910 30478909 29589016 30059225

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 30, 2:36 PM CDT	Tornado Watch	SPC	Ascension, East Baton Rouge, East Feliciana, Iberville, Livingston, Pointe Coupee and 6 more	3 hr
Sep 30, 5:09 PM CDT	Mesoscale Discussion	SPC	Saint Tammany, Washington	96 min
Sep 30, 5:50 PM CDT	Tornado Watch	SPC	Concordia, Madison, Orleans, Plaquemines, Saint Bernard, Saint Tammany and 3 more	8 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.