Sunday, September 23, 2007

WATCHES: Severe Thunderstorm Watch Number 685

WWUS20 KWNS 232025
SEL5
SPC WW 232025
NDZ000-NEZ000-SDZ000-240400-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 685
NWS STORM PREDICTION CENTER NORMAN OK
325 PM CDT SUN SEP 23 2007

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

PARTS OF CENTRAL NORTH DAKOTA
MUCH OF WESTERN NEBRASKA
MUCH OF CENTRAL AND PARTS OF WESTERN SOUTH DAKOTA

EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 325 PM UNTIL
1100 PM CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 85
STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES NORTHEAST OF
BISMARCK NORTH DAKOTA TO 65 MILES SOUTH OF MULLEN NEBRASKA. FOR
A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU5).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...STRONG COLD FRONT CURRENTLY MOVING INTO WRN SD/NEB
PANHANDLE WILL INITIATE STRONG/SEVERE THUNDERSTORMS AS IT ENCOUNTERS
AN UNSTABLE DEEPLY MIXED AIR MASS. STRONG DEEP LAYER SHEAR AHEAD OF
EJECTING TROUGH FROM THE ROCKIES WILL ENHANCE ALONG WITH STEEP LOW
LEVEL LAPSE RATES...DAMAGING WIND POTENTIAL AS STORMS MOVE/DEVELOP
RAPIDLY NE/NNEWD THRU THE EVENING.

AVIATION...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 500. MEAN STORM
MOTION VECTOR 21035.


..HALES

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