Tornado Watch 155

Issued

Apr 21, 2007, 2:30 PM CDT (19:30 UTC)

Expired

Apr 21, 2007, 10:35 PM CDT

In force

8 hr

Issued by

the Storm Prediction Center

Largest hail expected

2.5 in

Strongest gust expected

50 kt

The Aberdeen radar (KABR), 97 km from the middle of the area, began a volume at 19:31 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

10%

Ten or more severe hail reports

95%

One or more hailstones of 2 inches or more

30%

Six or more combined severe hail and wind reports

95%

• Mesoscale Discussion 524Apr 21, 1:35 PM CDT
• Mesoscale Discussion 529Apr 21, 6:20 PM CDT
• Mesoscale Discussion 532Apr 21, 7:56 PM CDT
• Mesoscale Discussion 533Apr 21, 8:16 PM CDT

000
WWUS20 KWNS 211932
SEL5  
SPC WW 211932
SDZ000-220400-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 155
NWS STORM PREDICTION CENTER NORMAN OK
230 PM CDT SAT APR 21 2007

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

       CENTRAL AND EASTERN SOUTH DAKOTA

EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 230 PM UNTIL
1100 PM CDT.

TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 60 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE
MILES EAST AND WEST OF A LINE FROM 35 MILES NORTH NORTHEAST OF
ABERDEEN SOUTH DAKOTA TO 60 MILES SOUTH SOUTHWEST OF CHAMBERLAIN
SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).

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 154...

DISCUSSION...TSTMS/SUPERCELLS EXPECTED TO DEVELOP IN WW OVER THE
NEXT 2 HOURS OR SO...WITH ADDITIONAL ACTIVITY LIKELY SPREADING NE
INTO WW FROM NEB.  STRENGTHENING/DECOUPLING LLJ THIS EVENING COULD
ENHANCE LOW LEVEL STORM ROTATION/TORNADO POTENTIAL AS LARGE SCALE
ASCENT INCREASES WITH APPROACH OF NM UPR VORT.  IN THE
MEANTIME...AMPLE SHEAR/INSTABILITY IS IN PLACE FOR SUPERCELLS WITH
LARGE HAIL AND POSSIBLY ISOLATED TORNADOES...ONCE CAP IS BREACHED
WITH CONVERGENCE ALONG EXISTING FRONTAL SEGMENTS/OUTFLOW BOUNDARIES.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 50 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
450. MEAN STORM MOTION VECTOR 22030.


...CORFIDI

Tornado Watches in South Dakota, 2007Every tornado watch in 2007

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.