Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 129

February 18, 20126 parishes in Louisiana; Harrison County, Jackson County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Feb 18, 2012, 2:21 PM CST for 6 parishes in Louisiana; Harrison County, Jackson County, Mississippi. It was in force for 24 min.

The area

The outline as issued.

The facts

Issued
Feb 18, 2012, 2:21 PM CST (20:21 UTC)
Expired
Feb 18, 2012, 2:45 PM CST
In force
24 min
Issued by
the Storm Prediction Center

Counties Jefferson Parish, LA, Lafourche Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, St. Mary Parish, LA, Terrebonne Parish, LA, Harrison County, MS, Jackson 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 12:00Z, 8.4 hours before the alert went out and 84 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 12:00Z on 2012-02-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 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 12:00Z on 2012-02-18The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 160 square meters per square second.1939587897117Sfc1 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
449 m above ground
0-6 km bulk shear
57 kt
0-1 km storm-relative helicity
160 m²/s²
0-3 km storm-relative helicity
177 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.

538 
ACUS11 KWNS 182022
SWOMCD
SPC MCD 182021
MSZ000-LAZ000-182045-

MESOSCALE DISCUSSION 0129
NWS STORM PREDICTION CENTER NORMAN OK
0221 PM CST SAT FEB 18 2012

AREAS AFFECTED...SERN LA...FAR SRN MS

CONCERNING...TORNADO WATCH 28...

VALID 182021Z - 182045Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 28 CONTINUES.

WW 28 IS SCHEDULED TO EXPIRE AT 21Z. A REPLACEMENT WW OR WFO
TEMPORAL EXTENSION WILL BE COORDINATED SHORTLY.

TRAILING PART OF LEAD LINE-SEGMENT IN FAR SRN MS MAY REMAIN WITHIN
THE FAR ERN PORTIONS OF WW 28 PRIOR TO THE 21Z WW EXPIRATION.
UPSTREAM...INTENSIFICATION OF TSTMS OFF THE SWRN LA COAST APPEARS
POSSIBLE GIVEN THE PRESENCE OF A WEAKLY UNSTABLE/NOT YET OVERTURNED
AIR MASS OVER FAR SERN LA. WITH 0-1 KM SHEAR AOA 35 KT...POTENTIAL
FOR EMBEDDED ROTATING UPDRAFTS APPEARS LIKELY TO PERSIST BEYOND 21Z
ACROSS FAR SERN LA/SRN MS...CAPABLE OF PRODUCING ISOLATED DAMAGING
WINDS/TORNADOES.

..GRAMS.. 02/18/2012

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

ATTN...WFO...LIX...LCH...

LAT...LON   28989099 29259159 29539179 29659174 29779149 29649073
            29759029 30358936 30668878 30588844 30388843 29218877
            28968908 28929063 28989099

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Feb 18, 4:35 AM CSTMesoscale DiscussionSPCCalcasieu, Cameron, Jefferson Davis, Vermilion55 min
Feb 18, 4:46 AM CSTSevere Thunderstorm WatchSPCAcadia, Calcasieu, Cameron, Jefferson Davis, Vermilion5 hr
Feb 18, 8:29 AM CSTMesoscale DiscussionSPCAcadia, Assumption, Cameron, Iberia, Iberville, Jefferson Davis and 4 more31 min
Feb 18, 9:31 AM CSTMesoscale DiscussionSPCAscension, Assumption, East Baton Rouge, Iberia, Iberville, Jefferson and 16 more59 min
Feb 18, 9:55 AM CSTTornado WatchSPCAscension, Assumption, East Baton Rouge, Iberia, Iberville, Jefferson and 15 more7 hr
Feb 18, 11:21 AM CSTMesoscale DiscussionSPCAscension, Assumption, Jefferson, Lafourche, Livingston, Orleans and 10 more54 min
Feb 18, 1:03 PM CSTMesoscale DiscussionSPCOrleans, Saint Bernard, Saint Charles57 min
Feb 18, 3:41 PM CSTMesoscale DiscussionSPCJefferson, Plaquemines, Saint Bernard64 min
Feb 18, 4:29 PM CSTMesoscale DiscussionSPCJefferson, Lafourche, Orleans, Plaquemines, Saint Bernard, Saint Charles and 1 more31 min
Feb 18, 4:48 PM CSTTornado WatchSPCLafourche, Plaquemines, Terrebonne4 hr
Feb 18, 11:49 AM CSTTornado WatchSPCGeorge, Stone5 hr
Feb 18, 2:02 PM CSTMesoscale DiscussionSPCGeorge, Harrison, Jackson58 min

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.