June 17 Severe Weather Blog

Tornado Watch has been issued south of the Twin Cities metro area until 1 AM.



URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 449
NWS STORM PREDICTION CENTER NORMAN OK
700 PM CDT WED JUN 17 2009

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

NORTH CENTRAL AND NORTHEAST IOWA
SOUTH CENTRAL AND SOUTHEAST MINNESOTA

EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 700 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 60 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 15 MILES WEST SOUTHWEST OF
FAIRMONT MINNESOTA TO 25 MILES SOUTH OF LA CROSSE WISCONSIN. 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 439...WW 440...WW
441...WW 442...WW 443...WW 445...WW 444...WW 446...WW 447...WW
448...

DISCUSSION...A VERY UNSTABLE ENVIRONMENT IS PRESENT ACROSS S/SE MN
INTO NRN IA...ALONG AND S OF A SURFACE WARM FRONT AND WEAK SURFACE
WAVE IN SRN MN. BOUNDARY LAYER DEWPOINTS IN THE 70S AND
TEMPERATURES IN THE 80S ARE CONTRIBUTING TO MLCAPE VALUES OF
3000-4000 J/KG...AND EFFECTIVE BULK SHEAR OVER THIS AREA IS AOA 50
KTS. THE ENVIRONMENT STRONGLY FAVORS DISCRETE SUPERCELL
DEVELOPMENT...WHILE THE RICH LOW-LEVEL MOISTURE AND 0-1 KM SRH AOA
200 M2/S2 WILL FAVOR TORNADIC SUPERCELLS. GIVEN THESE ENVIRONMENTAL
CONDITIONS...AN ISOLATED STRONG TORNADO MAY OCCUR. OTHERWISE...VERY
LARGE HAIL AND ISOLATED DAMAGING WINDS WILL BE POSSIBLE.

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
550. MEAN STORM MOTION VECTOR 29025.

...THOMPSON