MESOSCALE DISCUSSION 1099 NWS STORM PREDICTION CENTER NORMAN OK 0352 PM CDT FRI JUN 08 2012 AREAS AFFECTED...NERN MT CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 082052Z - 082145Z PROBABILITY OF WATCH ISSUANCE...40 PERCENT SUMMARY...A GRADUAL INCREASE IN TSTM COVERAGE IS EXPECTED THROUGH LATE AFTERNOON ACROSS NERN MT. THE ENVIRONMENT WILL BECOME INCREASINGLY FAVORABLE FOR LARGE HAIL AND ISOLATED DMGG WIND GUSTS...AND CONVECTIVE TRENDS WILL BE MONITORED FOR POTENTIAL WW ISSUANCE LATER THIS AFTERNOON AND EVENING. DISCUSSION...RECENT VISIBLE SATELLITE LOOP SHOWS INCREASING TOWERING CU FIELD /PRIMARILY ANCHORED TO THE HIGHER TERRAIN/ OVER PORTIONS OF CNTRL MT. ONE EXCEPTION IS A PERSISTENT/REGENERATING STORM OVER BLAINE COUNTY...WHICH HAS SHOWN RADAR INDICATIONS FOR POTENTIALLY SUB-SEVERE HAIL. STRONG SFC HEATING /TEMPS IN THE UPPER 70S AT 20Z/ ...UPSLOPE E-SELY LOW-LEVEL FLOW...AND INCREASING LARGE-SCALE ASCENT/HEIGHT FALLS ASSOCIATED WITH A POWERFUL NWRN CONUS UPPER TROUGH...SHOULD SUPPORT AN INCREASE IN TSTM COVERAGE DURING THE NEXT 2-3 HRS. THE EXACT EVOLUTION OF CONVECTION IS SOMEWHAT UNCERTAIN...BUT RECENT CONVECTION-ALLOWING GUIDANCE /INCLUDING THE 18Z WRF-HRRR/ INDICATES DISCRETE STORMS OR SMALL CLUSTERS SHOULD EVENTUALLY MOVE OFF THE HIGHER TERRAIN EWD TOWARDS THE HIGH PLAINS OF ERN MT. ALTHOUGH INSTABILITY APPEARS RATHER MARGINAL /MLCAPE VALUES AOB 500 J/KG PER MODIFIED 20Z GGW SOUNDING/...FURTHER HEATING AND MOISTURE ADVECTION FROM THE SE WILL CONTINUE TO DESTABILIZE THE ENVIRONMENT THROUGH THIS EVENING...BECOMING MORE FAVORABLE FOR SUSTAINING STRONG UPDRAFTS. ADDITIONALLY...ESELY LOW-LEVEL FLOW BENEATH MODERATE MIDLEVEL SWLYS WILL YIELD EFFECTIVE SHEAR VALUES OF 50-60 KTS. THIS ENVIRONMENT WILL BE FAVORABLE FOR SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND DMGG WIND GUSTS...AND MAY NECESSITATE ISSUANCE OF A WW BY THE EARLY EVENING. ..ROGERS/MEAD.. 06/08/2012 ATTN...WFO...BYZ...GGW...TFX...
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