Alert archive / Louisiana / Tornado Watches in 2011

Tornado Watch 888

November 16, 201119 parishes in Louisiana; 6 counties in Mississippi

The Storm Prediction Center issued this tornado watch at Nov 16, 2011, 2:49 AM CST for 19 parishes in Louisiana; 6 counties in Mississippi. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: Nov 16, 2011, 2:49 AM CST (08:49 UTC)
Expired: Nov 16, 2011, 10:00 AM CST
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 0.5 in
Strongest gust expected: 60 kt

All 25 counties

Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, Iberville Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, George County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Pearl River County, MS, Stone County, MS

What SPC expected

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

Two or more tornadoes: 40%
One or more EF2 to EF5 tornadoes: 20%
Ten or more severe wind reports: 20%
One or more gusts of 65 knots or more: 5%
Ten or more severe hail reports: 20%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Nov 16, 3:33 AM CST	Tornado Warning	LIX	Livingston, Saint Helena, Tangipahoa	42 min
Nov 16, 4:09 AM CST	Tornado Warning	LIX	Washington	36 min
Nov 16, 4:18 AM CST	Tornado Warning	LIX	Jefferson, Saint Charles	42 min
Nov 16, 4:52 AM CST	Tornado Warning	LIX	Lafourche, Terrebonne	23 min
Nov 16, 4:53 AM CST	Tornado Warning	LIX	Jefferson, Orleans, Saint Charles	37 min
Nov 16, 5:21 AM CST	Tornado Warning	LIX	Lafourche, Saint Charles	39 min
Nov 16, 6:15 AM CST	Severe Thunderstorm Warning	LIX	Saint Tammany	60 min
Nov 16, 7:22 AM CST	Severe Thunderstorm Warning	LIX	Jefferson, Lafourche, Plaquemines	68 min
Nov 16, 7:34 AM CST	Tornado Warning	LIX	Hancock, Harrison	41 min

Discussions around it

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

Mesoscale Discussion 2329Nov 16, 5:33 AM CST

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 8.8 hours before the alert went out and 35 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: 1734 J/kg
Mixed-layer CIN: -8 J/kg
Mixed-layer LCL: 661 m above ground
0-6 km bulk shear: 58 kt
0-1 km storm-relative helicity: 116 m²/s²
0-3 km storm-relative helicity: 166 m²/s²
Significant tornado parameter: 1.4
Supercell composite: 8.1

Open this sounding in Storm Lab

The text

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

107 
WWUS20 KWNS 160851
SEL8
SPC WW 160851
LAZ000-MSZ000-CWZ000-161600-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 888
NWS STORM PREDICTION CENTER NORMAN OK
250 AM CST WED NOV 16 2011

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

       SOUTHEASTERN LOUISIANA
       FAR SOUTHERN MISSISSIPPI
       COASTAL WATERS

EFFECTIVE THIS WEDNESDAY MORNING FROM 250 AM UNTIL 1000 AM CST.

TORNADOES...HAIL TO 0.5 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 60 STATUTE
MILES EAST AND WEST OF A LINE FROM 30 MILES NORTH NORTHEAST OF
SLIDELL LOUISIANA TO 45 MILES WEST SOUTHWEST OF BOOTHVILLE
LOUISIANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).

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 887...

DISCUSSION...TSTMS MAY INCREASE IN COVERAGE/STRENGTH OVER SE LA OVER
THE NEXT SEVERAL HOURS AS VEERING OF LOW LVL FLOW FARTHER W ENHANCES
LOW LVL CONVERGENCE BENEATH WRN-MOST PORTION OF EJECTING UPR
IMPULSE.  STRENGTH OF SFC SSWLY FLOW OVER AND S OF WW AREA /PER SFC
DATA/...QUALITY OF MOISTURE...AND STRENGTH OF DEEP WIND FIELD
SUGGEST POSSIBILITY FOR SUSTAINED SUPERCELLS WITH LOW LVL
MESOCYCLONES/TORNADOES.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 22035.


...CORFIDI

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Nov 15, 8:59 PM CST	Mesoscale Discussion	SPC	Acadia, Ascension, Assumption, Avoyelles, Catahoula, Concordia and 25 more	2 hr
Nov 16, 2:20 AM CST	Tornado Watch	SPC	Livingston, Saint Helena, Tangipahoa, Washington	8 hr
Nov 16, 5:33 AM CST	Mesoscale Discussion	SPC	Jefferson, Lafourche, Orleans, Saint Bernard, Saint Charles, Saint James and 5 more	87 min
Nov 16, 1:35 AM CST	Mesoscale Discussion	SPC	Attala, Choctaw, Clarke, Clay, Copiah, Covington and 26 more	115 min

Nearby

Tornado Watches in Louisiana, 2011 Tornado Watches in Mississippi, 2011 Every tornado watch in 2011

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.