

942 

WWUS20 KWNS 251929

SEL4

SPC WW 251929

MTZ000-SDZ000-WYZ000-260300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 684

NWS STORM PREDICTION CENTER NORMAN OK

130 PM MDT MON JUL 25 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHEAST MONTANA

       WESTERN SOUTH DAKOTA

       NORTHEAST WYOMING



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 130 PM UNTIL 900

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 75

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 75 MILES NORTH

NORTHWEST OF SHERIDAN WYOMING TO 55 MILES EAST NORTHEAST OF RAPID

CITY SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).



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 683...



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

INTENSITY THIS AFTERNOON INTO EVENING ALONG FAVORED TERRAIN AND

SYNOPTIC FRONT AS LARGE-SCALE FORCING IS AUGMENTED BY VORTICITY

MAXIMUM MOVING OUT OF WY.  AMBIENT AIR MASS IS HOT AND RELATIVELY

MOIST WITH MLCAPE VALUES OF 1500-2500 J/KG.  THOUGH MIDLEVEL WIND

FIELD IS NOT PARTICULARLY STRONG...AREA VAD AND FORECAST SOUNDING

DATA SHOW PRONOUNCED VEERING OF WINDS WITH HEIGHT WITH 35-40 KT OF

DEEP-LAYER SHEAR.  AS SUCH...GIVEN ENVIRONMENT WILL SUPPORT

SUPERCELL STORM MODES WITH A RISK FOR DAMAGING WINDS AND LARGE HAIL.



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 28020.





...MEAD

