

000 

WWUS20 KWNS 091902

SEL7

SPC WW 091902

MTZ000-NDZ000-SDZ000-WYZ000-100200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 497

NWS STORM PREDICTION CENTER NORMAN OK

100 PM MDT MON JUL 9 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EASTERN MONTANA

       WESTERN NORTH DAKOTA

       WESTERN SOUTH DAKOTA

       NORTHEAST WYOMING



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 100 PM UNTIL 800

PM MDT.



HAIL TO 1.5 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 60 MILES NORTH

NORTHWEST OF WILLISTON NORTH DAKOTA TO 60 MILES SOUTH SOUTHEAST

OF MOORCROFT WYOMING.  FOR A COMPLETE DEPICTION OF THE WATCH SEE

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).



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.



OTHER WATCH INFORMATION...CONTINUE...WW 494...WW 495...WW 496...



DISCUSSION...A STRONG SHORTWAVE TROUGH AND ASSOCIATED SURFACE

LOW/COLD FRONT WILL SURGE EWD/SEWD ACROSS MT INTO THE WRN DAKOTAS BY

LATE EVENING.  A RETURN FLOW OF UPPER 50 DEWPOINTS AND SURFACE

TEMPERATURES AOA 80F WILL CONTRIBUTE TO SUFFICIENT WARM SECTOR

INSTABILITY FOR SEVERE THUNDERSTORM DEVELOPMENT ALONG THE SURFACE

BOUNDARIES.  DEEP LAYER  SHEAR VECTOR MAGNITUDE AND ORIENTATION

SHOULD FAVOR SUPERCELL DEVELOPMENT INITIALLY...WHILE LATER THIS

EVENING STORMS MAY TEND TO GROW UPSCALE INTO A MORE LINEAR MCS ALONG

THE FRONT.  LARGE HAIL AND DAMAGING WINDS CAN BE EXPECTED WITH THE

STRONGER STORMS.  WHILE SUPERCELLS ARE EXPECTED...RELATIVELY MODEST

LOW-LEVEL MOISTURE/SHEAR SUGGEST THAT ANY TORNADO THREAT SHOULD BE

SOMEWHAT LIMITED.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 29030.





...THOMPSON

