WATCHES: Severe Thunderstorm Watch Number 538

WWUS20 KWNS 021743
SEL8
SPC WW 021743
MTZ000-SDZ000-WYZ000-030100-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 538
NWS STORM PREDICTION CENTER NORMAN OK
1145 AM MDT THU JUL 2 2009

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

SOUTHEAST MONTANA
WESTERN SOUTH DAKOTA
NORTHEAST WYOMING

EFFECTIVE THIS THURSDAY MORNING AND EVENING FROM 1145 AM UNTIL
700 PM MDT.

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 80
STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES SOUTHWEST OF
RAPID CITY SOUTH DAKOTA TO 60 MILES NORTH NORTHWEST OF MILES CITY
MONTANA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).

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...THUNDERSTORMS ARE ALREADY INCREASING ACROSS S-CENTRAL
MT/N-CENTRAL WY AND THE BLACK HILLS OF SD LATE THIS MORNING. THESE
WILL LIKELY CONTINUE INCREASING/INTENSIFYING THROUGH THE DAY AHEAD
OF SHORTWAVE TROUGH CRESTING UPPER RIDGE AS AIR MASS DESTABILIZES
OVER THE PLAINS. MODEST WLY FLOW ALOFT WILL SUSTAIN SUFFICIENT DEEP
LAYER SHEAR FOR SUPERCELLS...ALONG WITH PERSISTENT CLUSTERS/SMALL
LINES OF STORMS SPREADING ESEWD. LARGE HAIL AND DAMAGING WINDS WILL
BE PRIMARY SEVERE THREATS...ALTHOUGH AN ISOLATED TORNADO COULD OCCUR
WITH ANY PERSISTENT SUPERCELL.

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 28015.

...EVANS

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