MESOSCALE DISCUSSION 1051

        MESOSCALE DISCUSSION 1051     NWS STORM PREDICTION CENTER NORMAN OK     0149 PM CDT MON JUN 04 2012          AREAS AFFECTED...ERN WA...PARTS OF NRN/WRN/CNTRL ID...NERN     ORE...NWRN MT          CONCERNING...SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY           VALID 041849Z - 042015Z          PROBABILITY OF WATCH ISSUANCE...95 PERCENT          SUMMARY...THE THREAT FOR SEVERE THUNDERSTORMS WILL INCREASE THIS     AFTERNOON ACROSS PARTS OF THE NRN GREAT BASIN AND NRN ROCKIES. LARGE     HAIL AND DAMAGING WINDS WILL BE THE PRIMARY CONCERNS WITH THIS     ACTIVITY...AND A SVR TSTM WATCH WILL BE ISSUED BY 2000Z.          DISCUSSION...LARGE-SCALE ASCENT CONTINUES TO INCREASE OVER THE NRN     GREAT BASIN IN ADVANCE OF AN ERN PACIFIC SHORTWAVE     TROUGH...CURRENTLY IN THE PROCESS OF BECOMING NEGATIVELY     TILTED...WITH 500-MB HEIGHT FALLS IN EXCESS OF 60 GEOPOTENTIAL     METERS PER 12 HOURS OVERSPREADING THE AREA. ACCOMPANYING THIS     TROUGH...A BROAD RIBBON OF ASCENT INFERRED FROM WATER VAPOR IMAGERY     LIES ACROSS WRN WA AND WRN ORE INTO NRN CA AND IS ASSOCIATED WITH A     N-S-ORIENTED SHIELD OF MULTI-LAYERED CLOUDS. INSOLATION/DIABATIC     HEATING EAST OF THIS SHIELD IS CONTRIBUTING TO A DIFFERENTIAL     HEATING ZONE/EFFECTIVE FRONT ALONG WHICH LOW-LEVEL ASCENT OWING TO     BAROCLINIC CIRCULATIONS AUGMENTED BY OROGRAPHIC CIRCULATIONS WILL     CONTRIBUTE TO THE INITIATION OF CONVECTION THIS AFTERNOON. THIS     INITIATION MAY OCCUR AS EARLY AS 2100Z OVER THE MOUNTAINS FROM NERN     ORE INTO SERN WA INCLUDING THE WALLOWA AND BLUE MOUNTAINS.          ALONG THE EFFECTIVE FRONT LIES A SFC LOW...EAST OF WHICH A WARM     FRONT EXTENDS FARTHER EAST TOWARD SERN MT. AS THE SFC LOW     INTENSIFIES THROUGH THE DAY...THE WARM FRONT WILL ADVANCE     NORTHWARD...WHILE AMPLE PACIFIC MOISTURE -- PW VALUES IN EXCESS OF     0.9 INCH -- MOVES ACROSS THE AREA...SERVING TO MAINTAIN SFC     DEWPOINTS IN THE MIDDLE 40S TO THE LOWER 50S WITH VERTICAL MIXING.     THIS MOISTURE...ALONG WITH INSOLATION/DIABATIC HEATING AND STEEP     MID-LEVEL LAPSE RATES /E.G. 8.0 C PER KM ACCORDING TO 12Z BOISE ID     RAOB/...WILL SUPPORT THE DEVELOPMENT OF MLCAPE VALUES OF 500-1250     J/KG -- LARGEST WITHIN THE WARM SECTOR. GIVEN 50-100 KT OF SLY/SSWLY     MID/HIGH-LEVEL FLOW...DEEP SHEAR SHOULD BE MORE THAN SUFFICIENT FOR     CONVECTIVE ORGANIZATION INCLUDING BOWING LINE SEGMENTS...LINE ECHO     WAVE PATTERNS...AND PERHAPS ONE OR TWO TRANSIENT SUPERCELL     STRUCTURES OCCURRING INTO THE EVENING HOURS.          POTENTIAL CONVECTIVE HAZARDS WITH THESE FAST/NNEWD-NWD-MOVING STORMS     INCLUDE SVR WIND GUSTS AND SVR HAIL. SOME FORECAST SOUNDINGS ACROSS     THE AREA...PARTICULARLY NEAR THE WARM FRONT...SUGGEST RELATIVELY     BACKED SFC WINDS CONTRIBUTING TO MARKED HODOGRAPH CURVATURE IN THE     LOW LEVELS -- POTENTIALLY AUGMENTED BY LOCAL FLOW CHANNELING -- AND     A TORNADO THREAT CANNOT BE COMPLETELY RULED OUT. HOWEVER...THE ZONE     OF STRONGEST EFFECTIVE STORM-RELATIVE HELICITY WILL BE ACROSS PARTS     OF NRN/CNTRL ID AND ERN WA WHERE THE ELY COMPONENT OF THE LOW-LEVEL     FLOW WOULD FOLLOW DOWNSLOPE TRAJECTORIES YIELDING REDUCED     INSTABILITY. FURTHERMORE...RELATIVELY HIGH LFC/LCL HEIGHTS AND AT     LEAST MODEST SFC TEMPERATURE-DEWPOINT SPREADS...WILL ALSO ACT TO     LIMIT THE TORNADO POTENTIAL.          ..COHEN/CARBIN.. 06/04/2012               ATTN...WFO...PIH...MSO...BOI...OTX...PDT...