Tornado Watch 257

Issued

Apr 30, 2011, 5:55 PM CDT (22:55 UTC)

Expired

May 1, 2011, 2:00 AM CDT

In force

8 hr

Issued by

the Storm Prediction Center

Largest hail expected

2.5 in

Strongest gust expected

60 kt

The Shreveport radar (KSHV), 161 km from the middle of the area, began a volume at 22:57 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.

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

30%

Ten or more severe hail reports

40%

One or more hailstones of 2 inches or more

40%

Six or more combined severe hail and wind reports

70%

• Mesoscale Discussion 670Apr 30, 4:58 PM CDT
• Mesoscale Discussion 674Apr 30, 9:26 PM CDT
• Mesoscale Discussion 675Apr 30, 11:39 PM CDT
• Mesoscale Discussion 676May 1, 1:14 AM CDT
• Mesoscale Discussion 677May 1, 1:16 AM CDT

239 
WWUS20 KWNS 302259
SEL7
SPC WW 302259
ARZ000-OKZ000-TXZ000-010700-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 257
NWS STORM PREDICTION CENTER NORMAN OK
555 PM CDT SAT APR 30 2011

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

       SOUTHWEST ARKANSAS
       SOUTHEAST OKLAHOMA
       NORTHEAST TEXAS

EFFECTIVE THIS SATURDAY AFTERNOON AND SUNDAY MORNING FROM 555 PM
UNTIL 200 AM CDT.

TORNADOES...HAIL TO 2.5 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 70 STATUTE
MILES EAST AND WEST OF A LINE FROM 10 MILES SOUTHWEST OF TYLER
TEXAS TO 25 MILES NORTH NORTHWEST OF DE QUEEN ARKANSAS.  FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU7).

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...INCIPIENT STORM DEVELOPMENT IS UNDERWAY ALONG COLD
FRONT OVER THE DALLAS-FT. WORTH AREA WITHIN A STRONGLY UNSTABLE AIR
MASS WITH MLCAPE VALUES OF 3000 J/KG. KINEMATIC ENVIRONMENT INVOF
COLD FRONT IS CHARACTERIZED BY A WEAK LOW-LEVEL WIND FIELD BUT 40-50
KT EFFECTIVE BULK SHEAR.  HOWEVER...AS STORMS MATURE...THEY WILL
ENCOUNTER STRONGER LOW-LEVEL SHEAR AND HIGHER BOUNDARY LAYER
MOISTURE CONTENT WITH EWD EXTENT.  AS SUCH...INITIAL HAZARDS WILL BE
LARGE HAIL AND LOCALLY DAMAGING WINDS WITH AN INCREASED TORNADO
THREAT AFTER 01/00Z.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 24030.


...MEAD

Tornado Watches in Texas, 2011Tornado Watches in Arkansas, 2011Tornado Watches in Oklahoma, 2011Every tornado watch in 2011

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.