MESOSCALE DISCUSSION 0778
   NWS STORM PREDICTION CENTER NORMAN OK
   0607 PM CDT SAT MAY 12 2007
   
   AREAS AFFECTED...PARTS OF WRN AND CNTRL MT
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 267...
   
   VALID 122307Z - 130030Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 267
   CONTINUES.
   
   SCATTERED THUNDERSTORM ACTIVITY IS ONGOING...MOSTLY WITHIN A BELT OF
   BROAD ISENTROPIC ASCENT EXTENDING DOWNSTREAM OF SHORT WAVE TROUGH
   NOW PROGRESSING INTO THE PACIFIC NORTHWEST COAST.  LOW BOUNDARY
   LAYER MOISTURE LEVELS AND LOWER/MID TROPOSPHERIC WARMING APPEAR TO
   BE INHIBITING CONVECTIVE DEVELOPMENT...EXCEPT NEAR STRONGER
   OROGRAPHIC FORCING ASSOCIATED WITH THE MOUNTAINS OF WESTERN INTO
   CENTRAL MONTANA.  HOWEVER...MODELS ARE SUGGESTIVE THAT CONVECTIVE
   TEMPERATURES WILL BE REACHED IN THE PEAK HEATING...WITH INCREASING
   POTENTIAL FOR SCATTERED SURFACE BASED STORMS ACROSS THE GREAT
   FALLS/HAVRE/LEWISTOWN AREAS WITHIN THE NEXT HOUR OR TWO.  IF THIS
   OCCURS...SHEAR PROFILES BENEATH MODERATE WESTERLY 500 MB FLOW WILL
   BE SUFFICIENT FOR SUPERCELLS...ENHANCING SEVERE
   THREAT...PARTICULARLY FOR LARGE HAIL/DAMAGING DOWNBURSTS.
   
   OTHERWISE...IT SEEMS THAT A STRENGTHENING DIVERGENT UPPER FLOW FIELD
   WILL OVERSPREAD WESTERN MONTANA INTO THE NORTH CENTRAL INTERNATIONAL
   BORDER AREA OF MONTANA BY 00-03Z...MUCH AS SUGGESTED BY MODEL
   GUIDANCE.  AS THIS OCCURS...ONGOING HIGH BASED STORMS MAY
   CONSOLIDATE INTO A LARGER CONVECTIVE CLUSTER.  AND...EVAPORATIVE
   COOLING ASSOCIATED WITH SIZABLE TEMPERATURE/DEW POINTS SPREADS IN
   THE LOWER/MID-LEVELS WILL SUPPORT INCREASING DOWNBURST POTENTIAL.
   
   ..KERR.. 05/12/2007
   
   
   ATTN...WFO...BYZ...GGW...TFX...MSO...
   
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