Alert archive / Louisiana / Tornado Watches in 2015

Tornado Watch 549

November 17, 201512 parishes in Louisiana

The Storm Prediction Center issued this tornado watch at Nov 17, 2015, 3:33 PM CST for 12 parishes in Louisiana. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Nov 17, 2015, 3:33 PM CST (21:33 UTC)
Expired: Nov 17, 2015, 8:00 PM CST
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 0.5 in
Strongest gust expected: 60 kt

Counties Acadia Parish, LA, Allen Parish, LA, Avoyelles Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Evangeline Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Rapides Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Vermilion Parish, LA

The radar

The Lake Charles radar (KLCH), 55 km from the middle of the area, began a volume at 21:32 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: 40%
One or more EF2 to EF5 tornadoes: 20%
Ten or more severe wind reports: 30%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 10%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Nov 17, 6:08 PM CST	Severe Thunderstorm Warning	LCH	Avoyelles, Evangeline, Rapides, Saint Landry	37 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, 9.6 hours before the alert went out and 54 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: 1295 J/kg
Mixed-layer CIN: -2 J/kg
Mixed-layer LCL: 475 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 230 m²/s²
0-3 km storm-relative helicity: 307 m²/s²
Significant tornado parameter: 1.4
Supercell composite: 7.5

Open this sounding in Storm Lab

The text

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

060 
WWUS20 KWNS 172126
SEL9  
SPC WW 172126
LAZ000-CWZ000-180200-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 549
NWS STORM PREDICTION CENTER NORMAN OK
325 PM CST TUE NOV 17 2015

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* TORNADO WATCH FOR PORTIONS OF 
  SOUTHWEST INTO CENTRAL LOUISIANA
  COASTAL WATERS

* EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 325 PM UNTIL
  800 PM CST.

* PRIMARY THREATS INCLUDE...
  A COUPLE TORNADOES POSSIBLE
  ISOLATED DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

SUMMARY...THE SOUTHERN EXTENT OF A SQUALL LINE ONGOING OVER THE
LOWER MISSISSIPPI VALLEY WILL SLOWLY PROGRESS EAST ACROSS THE WATCH
AREA LATE THIS AFTERNOON AND THIS EVENING.  WHILE DAMAGING
STRAIGHT-LINE WINDS WILL BE THE PRIMARY HAZARD...A COUPLE OF
TORNADOES ARE POSSIBLE.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 45 STATUTE
MILES EAST AND WEST OF A LINE FROM 35 MILES SOUTHEAST OF LAKE
CHARLES LOUISIANA TO 5 MILES NORTHWEST OF ALEXANDRIA LOUISIANA. 
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU9).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 545...WW 546...WW
547...WW 548...

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
500. MEAN STORM MOTION VECTOR 22035.


...MEAD

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Nov 17, 8:24 AM CST	Mesoscale Discussion	SPC	Beauregard, Bienville, Bossier, Caddo, Claiborne, De Soto and 5 more	66 min
Nov 17, 8:55 AM CST	Tornado Watch	SPC	Acadia, Allen, Avoyelles, Beauregard, Bienville, Bossier and 25 more	7 hr
Nov 17, 12:19 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Avoyelles, Beauregard, Bienville and 40 more	116 min
Nov 17, 12:36 PM CST	Tornado Watch	SPC	Ascension, Catahoula, Concordia, East Baton Rouge, East Carroll, East Feliciana and 12 more	7 hr
Nov 17, 2:51 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Caldwell and 20 more	84 min
Nov 17, 5:54 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Avoyelles, Calcasieu, Cameron, Evangeline and 6 more	96 min

Nearby

Tornado Watches in Louisiana, 2015 Every tornado watch in 2015

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.