Tornado Watch 689

Issued

Jul 26, 2011, 5:21 PM CDT (22:21 UTC)

Expired

Jul 26, 2011, 10:26 PM CDT

In force

5 hr

Issued by

the Storm Prediction Center

Largest hail expected

2.5 in

Strongest gust expected

60 kt

The Aberdeen radar (KABR), 140 km from the middle of the area, began a volume at 22:21 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

50%

Six or more combined severe hail and wind reports

80%

• Mesoscale Discussion 1752Jul 26, 3:59 PM CDT
• Mesoscale Discussion 1759Jul 26, 8:10 PM CDT

889 
WWUS20 KWNS 262224
SEL9
SPC WW 262224
NDZ000-SDZ000-270600-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 689
NWS STORM PREDICTION CENTER NORMAN OK
525 PM CDT TUE JUL 26 2011

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

       SOUTH-CENTRAL NORTH DAKOTA
       CENTRAL SOUTH DAKOTA

EFFECTIVE THIS TUESDAY AFTERNOON AND WEDNESDAY MORNING FROM 525
PM UNTIL 100 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 75 STATUTE
MILES EAST AND WEST OF A LINE FROM 20 MILES WEST OF CHAMBERLAIN
SOUTH DAKOTA TO 85 MILES NORTH NORTHEAST OF MOBRIDGE SOUTH
DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED
WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).

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 686...WW 687...WW 688...

DISCUSSION...INCIPIENT SURFACE-BASED TSTM DEVELOPMENT IS UNDERWAY
FROM PIR-MBG...N OF SURFACE LOW AND ATTENDANT WARM FRONT.
MODIFICATION OF 20Z ABR SOUNDING FOR CURRENT SURFACE CONDITIONS NEAR
WARM FRONT SUGGESTS THAT CAP HAS BECOME QUITE WEAK WITH MLCAPE
VALUES AROUND 2000-3000 J/KG.  MOREOVER...STRENGTHENING MIDLEVEL
WIND FIELD ASSOCIATED WITH DE-AMPLIFYING SHORT WAVE TROUGH OVER THE
NRN HIGH PLAINS COUPLED WITH BACKED LOW-LEVEL FLOW N OF WARM FRONT
IS RESULTING IN A RATHER STRONGLY SHEARED ENVIRONMENT.  AS
SUCH...SETUP APPEARS FAVORABLE FOR SUPERCELL EVOLUTION WITH A RISK
FOR TORNADOES...LARGE HAIL AND LOCALLY DAMAGING WINDS.

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
600. MEAN STORM MOTION VECTOR 25020.


...MEAD

Tornado Watches in South Dakota, 2011Tornado Watches in North Dakota, 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.