

393 

WWUS20 KWNS 112156

SEL0

SPC WW 112156

MTZ000-NDZ000-SDZ000-120500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 410

NWS STORM PREDICTION CENTER NORMAN OK

450 PM CDT THU JUL 11 2013



THE NWS STORM PREDICTION CENTER HAS ISSUED A



* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

  FAR EASTERN MONTANA

  WESTERN NORTH DAKOTA

  NORTHWEST SOUTH DAKOTA



* EFFECTIVE THIS THURSDAY AFTERNOON FROM 450 PM UNTIL MIDNIGHT

  CDT.



* PRIMARY THREATS INCLUDE...

  SEVERAL DAMAGING WIND GUSTS WITH A FEW SIGNIFICANT GUSTS TO 75

    MPH POSSIBLE

  SEVERAL LARGE HAIL EVENTS WITH A FEW VERY LARGE HAIL EVENTS TO 2

    INCHES IN DIAMETER POSSIBLE

  A FEW TORNADOES POSSIBLE



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 75

STATUTE MILES EAST AND WEST OF A LINE FROM 65 MILES NORTH

NORTHEAST OF WILLISTON NORTH DAKOTA TO 40 MILES SOUTH OF BUFFALO

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

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).



PRECAUTIONARY/PREPAREDNESS ACTIONS...



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...TSTM DEVELOPMENT IS UNDERWAY OVER ERN MT AT THE

INTERSECTION OF AN EWD-MOVING COLD FRONT AND A QUASI-STATIONARY

BOUNDARY WHERE A LOCAL EROSION OF THE CAP HAS OCCURRED.  THE

PRESENCE OF STEEP LAPSE RATES AND A RELATIVELY MOIST PBL --NAMELY

ALONG AND E OF THE QUASI-STATIONARY BOUNDARY-- HAVE CONTRIBUTED TO A

MODERATE TO STRONGLY UNSTABLE AIR MASS WITH MLCAPE VALUES OF

2000-4000 J/KG.  WHEN COUPLED WITH A VERTICALLY VEERING WIND PROFILE

WITH 35-45 KT OF EFFECTIVE BULK SHEAR...THE SETUP WILL BE SUPPORTIVE

OF SUPERCELLS AS THE INITIAL STORM MODE WITH A RISK FOR PRIMARILY

LARGE HAIL AND DAMAGING WIND GUSTS.  THE GREATEST RISK FOR A TORNADO

WILL EXIST WITH ANY MATURE SUPERCELLS WHICH CROSS THE NNW-SSE

ORIENTED STATIONARY FRONT INTO WRN ND WHERE A LOWER LCL-STRONGER

LOW-LEVEL SHEAR ENVIRONMENT EXISTS.  OTHERWISE...EXPECT UPSCALE

GROWTH OF STORMS INTO CLUSTERS WITH A DAMAGING WIND AND HAIL THREAT

SPREADING EWD ACROSS WRN ND THIS EVENING INTO TONIGHT.



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

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 65

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 24020.





...MEAD

