Alert archive / Louisiana / Tornado Watches in 2007

Tornado Watch 741

December 20, 200736 parishes in Louisiana; 8 counties in Mississippi

The Storm Prediction Center issued this tornado watch at Dec 20, 2007, 9:15 AM CST for 36 parishes in Louisiana; 8 counties in Mississippi. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: Dec 20, 2007, 9:15 AM CST (15:15 UTC)
Expired: Dec 20, 2007, 3:58 PM CST
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1 in
Strongest gust expected: 60 kt

All 44 counties

Acadia Parish, LA, Allen Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Jefferson Parish, LA, Lafayette Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Pointe Coupee 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 Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Vermilion Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Amite County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Pearl River County, MS, Pike County, MS, Walthall County, MS, Wilkinson County, MS

The radar

The Lake Charles radar (KLCH), 118 km from the middle of the area, began a volume at 15:15 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What SPC expected

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

Two or more tornadoes: 30%
One or more EF2 to EF5 tornadoes: 10%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 30%
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: 70%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Dec 20, 9:25 AM CST	Severe Thunderstorm Warning	LCH	Calcasieu, Cameron	65 min
Dec 20, 9:30 AM CST	Severe Thunderstorm Warning	LIX	Walthall	30 min
Dec 20, 9:58 AM CST	Severe Thunderstorm Warning	LCH	Calcasieu	62 min
Dec 20, 10:31 AM CST	Severe Thunderstorm Warning	LCH	Jefferson Davis	29 min
Dec 20, 12:27 PM CST	Severe Thunderstorm Warning	LIX	Harrison, Jackson	33 min
Dec 20, 1:06 PM CST	Severe Thunderstorm Warning	LIX	Jackson	24 min
Dec 20, 3:01 PM CST	Tornado Warning	LIX	Orleans	19 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

Lake Charles Mun, LA (KLCH), launched 12:00Z, 3.3 hours before the alert went out and 116 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: 775 J/kg
Mixed-layer CIN: -6 J/kg
Mixed-layer LCL: 578 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 211 m²/s²
0-3 km storm-relative helicity: 252 m²/s²
Significant tornado parameter: 1.1
Supercell composite: 4.5

Open this sounding in Storm Lab

The text

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

978 
WWUS20 KWNS 201522
SEL1  
SPC WW 201522
LAZ000-MSZ000-CWZ000-202200-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 741
NWS STORM PREDICTION CENTER NORMAN OK
915 AM CST THU DEC 20 2007

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

       SOUTHERN LOUISIANA
       FAR SOUTHERN MISSISSIPPI
       COASTAL WATERS

EFFECTIVE THIS THURSDAY MORNING AND AFTERNOON FROM 915 AM UNTIL
400 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 70 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 45 MILES SOUTHWEST OF LAKE
CHARLES LOUISIANA TO 30 MILES EAST SOUTHEAST OF SLIDELL
LOUISIANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).

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.

DISCUSSION...UPPER TROUGH MOVING THROUGH AREA WILL MAINTAIN
THUNDERSTORMS ACROSS THE WATCH AREA INTO THE AFTERNOON HOURS.
DESPITE STORMS CURRENTLY BEING SLIGHTLY ELEVATED...SOME WARMING MAY
RESULT IN SOME STORMS BECOMING SURFACE BASED BY LATE MORNING.
INCREASING WLY WINDS ALOFT...PER 55 KT 1-2 KM ABOVE THE SURFACE AT
POE...INDICATE A  THREAT FOR WIND DAMAGE INTO THE AFTERNOON HOURS.
INSTABILITY WILL NOT BE PARTICULARLY STRONG...SBCAPES AROUND 500
J/KG...BUT WEAK SURFACE BOUNDARY FROM LCH TO SOUTH OF MSY AND STRONG
LOW/DEEP SHEAR MAY BE SUPPORTIVE OF AN ISOLATED TORNADO OR TWO.

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 400.
MEAN STORM MOTION VECTOR 25045.


...IMY

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 19, 10:12 PM CST	Mesoscale Discussion	SPC	Allen, Beauregard, Calcasieu, Sabine, Vernon	93 min
Dec 20, 3:30 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Beauregard, Bienville, Bossier, Caddo and 14 more	90 min
Dec 20, 8:48 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Avoyelles, Beauregard, Calcasieu and 19 more	57 min
Dec 20, 11:21 AM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, Beauregard and 30 more	84 min
Dec 20, 1:06 PM CST	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, East Feliciana, Iberia, Iberville and 21 more	84 min
Dec 20, 10:01 AM CST	Tornado Watch	SPC	Clarke, Covington, Forrest, George, Greene, Jasper and 6 more	5 hr
Dec 20, 1:03 PM CST	Mesoscale Discussion	SPC	Jackson	57 min

Nearby

Tornado Watches in Louisiana, 2007 Tornado Watches in Mississippi, 2007 Every tornado watch in 2007

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; radar from the NEXRAD Level II archive.