

080 

WWUS20 KWNS 292033

SEL8

SPC WW 292033

MTZ000-WYZ000-300400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 818

NWS STORM PREDICTION CENTER NORMAN OK

235 PM MDT MON AUG 29 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EASTERN MONTANA

       NORTHEAST WYOMING



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 235 PM UNTIL

1000 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 75

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES NORTH OF

BILLINGS MONTANA TO 75 MILES EAST SOUTHEAST OF BROADUS 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.



OTHER WATCH INFORMATION...CONTINUE...WW 816...WW 817...



DISCUSSION...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND

INTENSITY THIS AFTERNOON IN ADVANCE OF MIDLEVEL VORTICITY MAXIMUM

TRANSLATING ACROSS MT.  AMBIENT AIR MASS IS CHARACTERIZED BY STEEP

LAPSE RATES...BOUNDARY LAYER DEWPOINTS IN THE MID 50S TO LOWER 60S

AND A GRADUALLY STRENGTHENING DEEP-LAYER WIND FIELD.  AS SUCH...THE

POTENTIAL WILL EXIST FOR ORGANIZED STORM MODES...INCLUDING

SUPERCELLS AND BOWS WITH ATTENDANT THREATS FOR DAMAGING WINDS AND

LARGE HAIL.



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 27030.





...MEAD

