Alert archive / Louisiana / Tornado Watches in 2012
Tornado Watch 71
The Storm Prediction Center issued this tornado watch at Mar 11, 2012, 11:55 AM CDT for 24 parishes in Louisiana; 22 counties in Texas. It was in force for 7 hr.
The area
The outline as issued.
The facts
- Issued
- Mar 11, 2012, 11:55 AM CDT (16:55 UTC)
- Expired
- Mar 11, 2012, 7:00 PM CDT
- In force
- 7 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 46 counties
Allen Parish, LA, Beauregard Parish, LA, Bienville Parish, LA, Bossier Parish, LA, Caddo Parish, LA, Calcasieu Parish, LA, Caldwell Parish, LA, Cameron Parish, LA, Claiborne Parish, LA, De Soto Parish, LA, Grant Parish, LA, Jackson Parish, LA, Jefferson Davis Parish, LA, LaSalle Parish, LA, Lincoln Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Red River Parish, LA, Sabine Parish, LA, Union Parish, LA, Vernon Parish, LA, Webster Parish, LA, Winn Parish, LA, Angelina County, TX, Chambers County, TX, Galveston County, TX, Gregg County, TX, Hardin County, TX, Harrison County, TX, Jasper County, TX, Jefferson County, TX, Liberty County, TX, Marion County, TX, Nacogdoches County, TX, Newton County, TX, Orange County, TX, Panola County, TX, Polk County, TX, Rusk County, TX, Sabine County, TX, San Augustine County, TX, San Jacinto County, TX, Shelby County, TX, Trinity County, TX, Tyler County, TX
The radar
The Shreveport radar (KSHV), 88 km from the middle of the area, began a volume at 16:56 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
- 50%
- One or more gusts of 65 knots or more
- 10%
- 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
5 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 11, 2:12 PM CDT | Tornado Warning | SHV | Sabine, San Augustine, Shelby | 48 min |
| Mar 11, 3:01 PM CDT | Severe Thunderstorm Warning | SHV | Sabine | 44 min |
| Mar 11, 3:55 PM CDT | Tornado Warning | SHV | Sabine | 50 min |
| Mar 11, 4:05 PM CDT | Tornado Warning | SHV | De Soto, Natchitoches, Red River | 40 min |
| Mar 11, 4:38 PM CDT | Severe Thunderstorm Warning | SHV | Natchitoches, Sabine | 49 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
Shreveport, LA (KSHV), launched 12:00Z, 4.9 hours before the alert went out and 93 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.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 419 m above ground
- 0-6 km bulk shear
- 50 kt
- 0-1 km storm-relative helicity
- 328 m²/s²
- 0-3 km storm-relative helicity
- 390 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 1.0
The text
As transmitted, in the capitals the NWS used until 2016.
978
WWUS20 KWNS 111700
SEL1
SPC WW 111700
LAZ000-TXZ000-CWZ000-120000-
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 71
NWS STORM PREDICTION CENTER NORMAN OK
1155 AM CDT SUN MAR 11 2012
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
SOUTHWEST AND NORTHERN LOUISIANA
EAST TEXAS
COASTAL WATERS
EFFECTIVE THIS SUNDAY MORNING AND EVENING FROM 1155 AM UNTIL 700
PM CDT.
TORNADOES...HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 75 STATUTE
MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH NORTHEAST OF
SHREVEPORT LOUISIANA TO 25 MILES SOUTH OF PORT ARTHUR TEXAS. 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...STORMS ARE GRADUALLY INCREASING IN INTENSITY OVER SERN
TX AS THE SRN END OF A SHORT WAVE TROUGH ROTATES NEWD ACROSS CENTRAL
TX. STRONG SOUTHERLY LOW LEVEL WINDS ARE TRANSPORTING MOISTURE NWD
TOWARD THE ARKLATEX REGION...WITH SUBSEQUENT DESTABILIZATION
EXPECTED THROUGH THE AFTERNOON. LATEST KHGX VWP INDICATES STRONG
LOW- AND DEEP LAYER SHEAR ASSOCIATED WITH A CLOCKWISE TURNING
HODOGRAPH FAVORABLE FOR SUPERCELLS AND A THREAT FOR A FEW TORNADOES
TO DEVELOP. ACTIVITY WILL DEVELOP NEWD WITH ADDITIONAL RISK FOR
DAMAGING WIND GUSTS WITHIN SMALL-SCALE BOWING LINE SEGMENTS.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 23035.
...WEISSSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 11, 11:31 AM CDT | Mesoscale Discussion | SPC | Bossier, Caddo, De Soto, Red River, Sabine | 89 min |
| Mar 11, 2:47 PM CDT | Mesoscale Discussion | SPC | Allen, Beauregard, Bienville, Calcasieu, De Soto, Grant and 10 more | 118 min |
| Mar 11, 5:36 PM CDT | Mesoscale Discussion | SPC | Avoyelles, Caldwell, Catahoula, Concordia, East Carroll, Franklin and 12 more | 84 min |
| Mar 11, 6:42 PM CDT | Tornado Watch | SPC | Acadia, Allen, Avoyelles, Caldwell, Cameron, Catahoula and 20 more | 8 hr |
| Mar 11, 7:56 AM CDT | Mesoscale Discussion | SPC | Angelina, Brazoria, Chambers, Fort Bend, Galveston, Hardin and 15 more | 3 hr |
Nearby
Tornado Watches in Louisiana, 2012Tornado Watches in Texas, 2012Every 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; radar from the NEXRAD Level II archive.