

129 

WWUS20 KWNS 151923

SEL4

SPC WW 151923

IAZ000-MNZ000-SDZ000-160100-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 664

NWS STORM PREDICTION CENTER NORMAN OK

220 PM CDT WED SEP 15 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       NORTHWEST IOWA

       SOUTHWEST MINNESOTA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 220 PM UNTIL

800 PM CDT.



TORNADOES...HAIL TO 2 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 NORTH AND SOUTH OF A LINE FROM 15 MILES WEST NORTHWEST OF

MITCHELL SOUTH DAKOTA TO 50 MILES EAST SOUTHEAST OF MANKATO

MINNESOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).



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...A SURFACE LOW WAS SITUATED ACROSS SERN SD WITH A

OUTFLOW REINFORCED WARM FRONT EXTENDING EAST TO ALONG IA/MN BORDER

AREA. STRONG DEVELOPMENT/INTENSIFICATION IS INDICATED IN LATEST

MODEL GUIDANCE AS SHORT WAVE TROUGH AMPLIFIES ACROSS THE REGION

THROUGH TONIGHT. AS DEVELOPING CONVECTION TAPS GREATER SURFACE-BASED

INSTABILITY COINCIDENT WITH LOW DEVELOPMENT AND STRENGTHENING LARGE

SCALE FORCING...EXPECT THE CHANCE FOR SEVERE WEATHER TO INCREASE.

INITIALLY DISCRETE STORMS WILL HAVE SOME POTENTIAL FOR DEEP ROTATION

AND HAIL PRODUCTION...WHILE ACTIVITY NEAR THE DEEPENING LOW AND

ALONG THE WARM FRONT WILL BE FAVORED FOR STRONGER LOW LEVEL ROTATION

AND TORNADIC POTENTIAL. WITH TIME...WIND DAMAGE THREAT MAY INCREASE

AS STORM COVERAGE INCREASES AMIDST STRENGTHENING DEEP-LAYER WIND

FIELDS.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

450. MEAN STORM MOTION VECTOR 27025.





...CARBIN

