MESOSCALE DISCUSSION 1684
   NWS STORM PREDICTION CENTER NORMAN OK
   0244 PM CDT THU AUG 02 2012
   
   AREAS AFFECTED...ERN MT/WRN ND/NERN WY/WRN SD
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 021944Z - 022015Z
   
   PROBABILITY OF WATCH ISSUANCE...80 PERCENT
   
   SUMMARY...A SEVERE TSTM WATCH WILL LIKELY BE NEEDED PRIOR TO 20Z
   ACROSS MUCH OF FAR ERN MT...NERN WY INTO WRN ND AND NWRN SD. 
   PRIMARY THREATS WILL BE DAMAGING WINDS AND LARGE HAIL.
   
   DISCUSSION...AFTERNOON SURFACE ANALYSIS SHOWED AN AREA OF LOW
   PRESSURE CENTERED OVER EAST CENTRAL MT WITH A DRY LINE/LEE TROUGH
   EXTENDING SWD THROUGH SERN MT INTO ERN WY.  REGIONAL RADAR IMAGERY
   INDICATED A FEW TSTMS HAVE ALREADY DEVELOPED ALONG THE DRY LINE IN
   CUSTER AND POWDER RIVER COUNTIES MT AND NERN JOHNSON AND CAMPBELL
   COUNTIES WY.  DESPITE MARGINAL MOISTURE /SURFACE DEWPOINTS IN THE
   UPPER 40S TO LOWER 50S/...OBJECTIVE ANALYSES INDICATED THE AIR MASS
   HAS BECOME MODERATELY UNSTABLE WITH MLCAPE UP TO 1500 J/KG ALONG AND
   E OF THE DRY LINE.
   
   THE PRIMARY THREAT AREA IS EXPECTED TO BE OVER ERN MT TO NERN WY
   WITH ACTIVITY SPREADING EWD INTO WRN ND AND NWRN SD.  OTHER ONGOING
   STORMS OVER EAST CENTRAL MT INTO WRN/SWRN ND ARE ATTENDANT TO LOW
   LEVEL WAA AND ARE NOT EXPECTED TO BECOME SEVERE DUE TO LIMITED
   INSTABILITY WITH EWD EXTENT.  THUS...ADDITIONAL SURFACE HEATING E OF
   THE DRY LINE WILL FURTHER DESTABILIZE THE AIR MASS.  THIS COMBINED
   WITH MORE THAN SUFFICIENT BULK SHEAR AROUND 35 KT...MULTICELLS AND A
   FEW SUPERCELLS WILL BE POSSIBLE. DAMAGING WINDS WILL BE A THREAT
   GIVEN THE DEEPLY MIXED BOUNDARY LAYER...STEEP LOW LEVEL LAPSE RATES
   AND LARGE DCAPE OF 1000-2000 J/KG.  STEEP MIDLEVEL LAPSE RATES WILL
   INCREASE THE HAIL THREAT.
   
   ..PETERS/WEISS.. 08/02/2012
   
   
   ATTN...WFO...ABR...BIS...UNR...BYZ...GGW...RIW...
   
   LAT...LON   44210605 45540581 47280671 48320666 48600472 48530296
               48110233 46400184 45680156 44250306 43950443 44210605