MESOSCALE DISCUSSION 0669
   NWS STORM PREDICTION CENTER NORMAN OK
   0537 PM CDT SAT MAY 21 2016

   AREAS AFFECTED...ERN MT...N-CNTRL/NERN WY

   CONCERNING...SEVERE THUNDERSTORM WATCH 188...

   VALID 212237Z - 212330Z

   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 188
   CONTINUES.

   SUMMARY...LARGE HAIL AND DMGG WINDS REMAIN THE PRIMARY THREATS
   ACROSS WW 188...AND A BRIEF TORNADO CANNOT BE RULED
   OUT...PARTICULARLY WITH A LONGER-LIVED SUPERCELL ACROSS NWRN ROSEBUD
   COUNTY IN MT. ADDITIONAL TSTMS MAY DEVELOP IN THE NEXT 1-2 HRS NEAR
   SHERIDAN COUNTY WY INTO SERN MT.

   DISCUSSION...FORCING FOR ASCENT ASSOCIATED WITH A STRONG UPPER JET
   NOSING INTO ERN MT CONTINUES TO INCREASE ALONG A MERIDIONALLY
   ORIENTED COLD FRONT. THE DOMINANT STORM IS CURRENTLY A LONG-LIVED
   SUPERCELL NE OF BILLINGS...MOVING ACROSS NWRN ROSEBUD COUNTY
   MT...WITH A HISTORY OF PRODUCING LARGE HAIL. A BROAD AREA OF SFC
   PRESSURE FALLS WAS OCCURRING AHEAD OF THE COLD FRONT...WHERE THE
   ENVIRONMENT ALSO REMAINS FAVORABLE FOR MAINTAINING SUPERCELL OR
   ORGANIZED CLUSTER CONVECTIVE MODES WITH BACKED SELY FLOW AND
   WIDESPREAD MID-UPPER 50S F DEWPOINTS OBSERVED. AN ACCOMPANYING SVR
   THREAT WILL CONTINUE SPREADING N-NEWD ACROSS NERN MT IN THE NEXT 1-2
   HRS.

   ACROSS S-CNTRL MT INTO FAR N-CNTRL WY...AN AREA OF HIGH-BASED
   CONVECTION IS APPROACHING THE DRYLINE AND SYNOPTIC SFC LOW CENTERED
   JUST N OF KSHR. A FEW STRONGER/SUSTAINED TSTMS COULD EVOLVE OUT OF
   THIS AREA AS THE ENVIRONMENT BECOMES MORE FAVORABLE FOR DEEP
   CONVECTION FARTHER N...AND MAY AFFECT SERN PORTIONS OF WW 188 WITH
   AN ACCOMPANYING LARGE-HAIL/WIND THREAT POSSIBLE.

   ..ROGERS.. 05/21/2016


   ATTN...WFO...UNR...BYZ...GGW...RIW...TFX...

   LAT...LON   44950569 44140643 44080693 44670780 45370842 45670865
               46080900 47010906 47600888 49000823 49000769 49000736
               49000650 49000637 49000611 48550580 48220580 44950569