Alert archive / Louisiana / Tornado Watches in 2015

Tornado Watch 101

April 24, 201512 parishes in Louisiana

The Storm Prediction Center issued this tornado watch at Apr 24, 2015, 3:15 PM CDT for 12 parishes in Louisiana. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Apr 24, 2015, 3:15 PM CDT (20:15 UTC)
Expired: Apr 24, 2015, 7:48 PM CDT
In force: 5 hr
Issued by: the Storm Prediction Center
Largest hail expected: 3 in
Strongest gust expected: 60 kt

Counties Ascension Parish, LA, Assumption Parish, LA, Iberville Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Terrebonne Parish, LA

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: 20%
Ten or more severe wind reports: 20%
One or more gusts of 65 knots or more: 20%
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: 60%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Apr 24, 3:27 PM CDT	Severe Thunderstorm Warning	LIX	Iberville	48 min
Apr 24, 4:03 PM CDT	Severe Thunderstorm Warning	LIX	Ascension, Assumption, Iberville	42 min
Apr 24, 4:38 PM CDT	Severe Thunderstorm Warning	LIX	Ascension, Assumption, Lafourche, Saint James, Saint John the Baptist	52 min
Apr 24, 5:22 PM CDT	Severe Thunderstorm Warning	LIX	Lafourche, Saint Charles, Saint James, Saint John the Baptist	38 min
Apr 24, 5:57 PM CDT	Severe Thunderstorm Warning	LIX	Jefferson, Lafourche, Plaquemines, Saint Charles	48 min
Apr 24, 6:41 PM CDT	Severe Thunderstorm Warning	LIX	Jefferson, Plaquemines, Saint Bernard	34 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, 8.3 hours before the alert went out and 123 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: 107 J/kg
Mixed-layer CIN: -406 J/kg
Mixed-layer LCL: 763 m above ground
0-6 km bulk shear: 44 kt
0-1 km storm-relative helicity: 130 m²/s²
0-3 km storm-relative helicity: 114 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

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

809 
WWUS20 KWNS 242013
SEL1  
SPC WW 242013
LAZ000-250100-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 101
NWS STORM PREDICTION CENTER NORMAN OK
315 PM CDT FRI APR 24 2015

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* TORNADO WATCH FOR PORTIONS OF 
  SOUTHEAST LOUISIANA

* EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 315 PM UNTIL
  800 PM CDT.

* PRIMARY THREATS INCLUDE...
  A COUPLE TORNADOES POSSIBLE
  SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 3
    INCHES IN DIAMETER POSSIBLE
  ISOLATED DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

SUMMARY...INTENSE SUPERCELL SHOULD TRACK EAST-SOUTHEAST ACROSS
SOUTHEAST LOUISIANA THROUGH EARLY EVENING.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 45 STATUTE
MILES EAST AND WEST OF A LINE FROM 20 MILES NORTHEAST OF BATON
ROUGE LOUISIANA TO 25 MILES SOUTH OF HOUMA LOUISIANA.  FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU1).

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 99...WW 100...

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
550. MEAN STORM MOTION VECTOR 29020.


...GRAMS/MEAD

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 24, 10:29 AM CDT	Mesoscale Discussion	SPC	Allen, Beauregard, Calcasieu, Jefferson Davis	91 min
Apr 24, 11:53 AM CDT	Mesoscale Discussion	SPC	Acadia, Allen, Assumption, Beauregard, Calcasieu, Cameron and 7 more	97 min
Apr 24, 12:18 PM CDT	Tornado Watch	SPC	Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 10 more	5 hr
Apr 24, 1:58 PM CDT	Mesoscale Discussion	SPC	Acadia, Ascension, Assumption, Cameron, East Baton Rouge, Iberia and 15 more	92 min
Apr 24, 3:58 PM CDT	Mesoscale Discussion	SPC	Bienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 15 more	92 min
Apr 24, 4:45 PM CDT	Tornado Watch	SPC	Bienville, Bossier, Caddo, Claiborne, De Soto, Jackson and 7 more	5 hr

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.