Alert archive / Louisiana / Tornado Watches in 2012

Tornado Watch 692

December 25, 201225 parishes in Louisiana

The Storm Prediction Center issued this tornado watch at Dec 25, 2012, 7:28 AM CST for 25 parishes in Louisiana. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Dec 25, 2012, 7:28 AM CST (13:28 UTC)
Expired: Dec 25, 2012, 12:58 PM CST
In force: 6 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1 in
Strongest gust expected: 60 kt

All 25 counties

Acadia Parish, LA, Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson 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 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

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 60%
One or more EF2 to EF5 tornadoes: 30%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 30%
Ten or more severe hail reports: 40%
One or more hailstones of 2 inches or more: 30%
Six or more combined severe hail and wind reports: 70%

Warnings issued inside it

2 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Dec 25, 12:37 PM CST	Severe Thunderstorm Warning	LCH	Allen, Avoyelles, Beauregard, Evangeline, Rapides, Saint Landry and 1 more	53 min
Dec 25, 12:51 PM CST	Severe Thunderstorm Warning	LCH	Acadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline and 3 more	54 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 1.5 hours before the alert went out and 139 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: 790 J/kg
Mixed-layer CIN: -14 J/kg
Mixed-layer LCL: 576 m above ground
0-6 km bulk shear: 46 kt
0-1 km storm-relative helicity: 181 m²/s²
0-3 km storm-relative helicity: 237 m²/s²
Significant tornado parameter: 1.1
Supercell composite: 10.0

Open this sounding in Storm Lab

The text

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

922 
WWUS20 KWNS 251326
SEL2
SPC WW 251326
LAZ000-CWZ000-251900-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 692
NWS STORM PREDICTION CENTER NORMAN OK
725 AM CST TUE DEC 25 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

       SOUTHERN LOUISIANA
       COASTAL WATERS

EFFECTIVE THIS TUESDAY MORNING AND AFTERNOON FROM 725 AM UNTIL
100 PM CST.

TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 50 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 5 MILES NORTHWEST OF
LAFAYETTE LOUISIANA TO 5 MILES SOUTH SOUTHEAST OF SLIDELL
LOUISIANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

OTHER WATCH INFORMATION...CONTINUE...WW 691...

DISCUSSION...TSTMS HAVE RECENTLY INTENSIFIED OVER S-CNTRL
LA...APPARENTLY IN RESPONSE TO A LOW-LATITUDE PERTURBATION
TRANSLATING ENEWD ALONG THE IMMEDIATE COAST.  12Z LCH/LIX SOUNDINGS
SHOWED THE PRESENCE OF A MOIST AND MODERATELY UNSTABLE AIR MASS WITH
A WEAKENING CAP WITH EWD EXTENT ACROSS THE WATCH AREA.  GIVEN THE
PRESENCE OF ALREADY SUFFICIENT LOW-LEVEL AND DEEP-LAYER SHEAR FOR
SUPERCELLS...A RISK FOR TORNADOES AND LOCALLY DAMAGING WINDS WILL
EXIST WITH ANY SUSTAINED STORMS.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500.
MEAN STORM MOTION VECTOR 23030.


...MEAD

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 25, 1:01 AM CST	Mesoscale Discussion	SPC	Allen, Beauregard, Sabine, Vernon	59 min
Dec 25, 1:37 AM CST	Severe Thunderstorm Watch	SPC	Acadia, Allen, Avoyelles, Beauregard, Calcasieu, De Soto and 9 more	7 hr
Dec 25, 5:56 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Avoyelles, Beauregard, Calcasieu, De Soto and 10 more	94 min
Dec 25, 7:00 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Beauregard, Calcasieu and 24 more	60 min
Dec 25, 8:46 AM CST	Mesoscale Discussion	SPC	Allen, Avoyelles, Beauregard, Bienville, Calcasieu, Caldwell and 21 more	59 min
Dec 25, 9:02 AM CST	Severe Thunderstorm Watch	SPC	Bienville, Bossier, Caddo, Caldwell, Catahoula, Claiborne and 20 more	7 hr
Dec 25, 9:17 AM CST	Tornado Watch	SPC	Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 10 more	8 hr
Dec 25, 12:19 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, Beauregard and 35 more	71 min
Dec 25, 12:23 PM CST	Mesoscale Discussion	SPC	Bienville, Caldwell, Catahoula, Concordia, East Carroll, Franklin and 13 more	67 min
Dec 25, 12:58 PM CST	Tornado Watch PDS	SPC	Ascension, Assumption, Catahoula, Concordia, East Baton Rouge, East Feliciana and 20 more	9 hr
Dec 25, 3:22 PM CST	Mesoscale Discussion	SPC	Caldwell, East Carroll, Morehouse, Richland, West Carroll	53 min
Dec 25, 3:44 PM CST	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, East Feliciana, Iberia, Iberville and 19 more	91 min

Nearby

Tornado Watches in Louisiana, 2012 Every tornado watch 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.