

377 

WWUS20 KWNS 162058

SEL7

SPC WW 162058

MTZ000-NDZ000-SDZ000-170400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 487

NWS STORM PREDICTION CENTER NORMAN OK

255 PM MDT MON JUL 16 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EXTREME SOUTHEAST MONTANA

       SOUTHWEST NORTH DAKOTA

       NORTHWEST SOUTH DAKOTA



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 255 PM UNTIL

1000 PM MDT.



HAIL TO 2.5 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 55

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 50 MILES SOUTH

SOUTHWEST OF BAKER MONTANA TO 30 MILES EAST NORTHEAST OF MOBRIDGE

SOUTH DAKOTA.  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.



DISCUSSION...SEVERE STORMS ARE EXPECTED TO INCREASE AND DEVELOP EAST

OFF THE HIGHER TERRAIN OF SERN MT AND WRN SD OVER THE NEXT COUPLE OF

HOURS. DOWNSTREAM AIR MASS IS CHARACTERIZED BY STRONG INSTABILITY

WHERE MOIST POST-FRONTAL LOW LEVEL ELY FLOW IS TOPPED BY 25-30KT

SWLY FLOW ALOFT. RESULTING SHEAR AND THERMODYNAMIC REGIME SHOULD

SUPPORT SUPERCELLS IF STORMS CAN PERSIST AND OVERCOME REMAINING

INHIBITION EAST OF THE HIGHER TERRAIN. DESPITE WARM TEMPERATURES

ALOFT...PERSISTENT LOW LEVEL CONVERGENCE ALONG THE FRONT AND

THERMAL/TRIPLE-POINT LOW...AND MAGNITUDE OF HEATING ALONG AND SOUTH

OF THE FRONTAL ZONE...SHOULD ACT TO OVERCOME REMAINING INHIBITION

AND FAVOR AT LEAST A FEW SEVERE STORMS PRODUCING LARGE HAIL AND HIGH

WINDS SPREADING EAST NEAR THE SD/ND BORDER AREA INTO THIS EVENING.



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

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 27025.





...CARBIN

