MESOSCALE DISCUSSION 1071

        MESOSCALE DISCUSSION 1071     NWS STORM PREDICTION CENTER NORMAN OK     0154 PM CDT TUE JUN 05 2012          AREAS AFFECTED...SWRN/S-CNTRL MT...NWRN WY...PARTS OF SERN ID          CONCERNING...SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY           VALID 051854Z - 052100Z          PROBABILITY OF WATCH ISSUANCE...95 PERCENT          SUMMARY...THE THREAT FOR SVR THUNDERSTORMS WILL INCREASE THIS     AFTERNOON AS A POTENT PACIFIC STORM SYSTEM AFFECTS THE NRN     ROCKIES...WITH DAMAGING WINDS AND SEVERE HAIL OF CONCERN ACROSS     PARTS OF THE AREA. THE SVR THREAT WILL BE GREATEST ACROSS     S-CNTRL/SWRN MT...WHERE A SEVERE THUNDERSTORM WATCH WILL BE NEEDED     BY 20Z-21Z.          DISCUSSION...VISIBLE SATELLITE IMAGERY INDICATES THAT TOWERING     CUMULUS CONTINUES TO DEVELOP OVER THE MOUNTAINS OF SWRN MONTANA AND     ADJACENT PARTS OF WRN WY AND SERN ID...INCLUDING THE     GALLATIN...ABSAROKA...AND TETON RANGES. THIS IS PARTLY IN RESPONSE     TO DESTABILIZATION IN ASSOCIATION WITH /1/ INCREASING LARGE-SCALE     ASCENT IN ADVANCE OF A POTENT PACIFIC TROUGH...WITH 500-MB HEIGHT     FALLS IN EXCESS OF 90 GEOPOTENTIAL METERS PER 12 HRS...ALONG WITH     /2/ WIDESPREAD INSOLATION/DIABATIC HEATING. IN ADDITION TO     OROGRAPHICALLY-INDUCED ASCENT...MESOSCALE ASCENT IS ALSO BEING     SUPPORTED BY A COLD FRONT CROSSING THE REGION IN ASSOCIATION WITH     THE TROUGH...ROUGHLY EXTENDING FROM A SFC LOW NEAR BOZEMAN MT SWD     TOWARD SALT LAKE CITY UT. A WEAKENING STATIONARY FRONT EXTENDS ENE     OF THE SFC LOW INTO E-CNTRL MT...WITH A DEVELOPING WARM FRONT INTO     N-CNTRL MT.          ADDITIONAL DIURNAL HEATING...COMBINED WITH MODEST LOW-LEVEL MOISTURE     SOUTH OF THE STATIONARY FRONT/DEVELOPING WARM FRONT -- SFC DEWPOINTS     PRIMARILY IN THE MID 30S TO THE 40S -- WILL YIELD MLCAPE VALUES OF     400-1000 J/KG. THE HIGHEST OF THESE VALUES WILL BE IN     MONTANA...WHERE VERTICAL MIXING HAS NOT BEEN AS STRONG AS FARTHER     SOUTH ACROSS WY/ID AS WY/ID DEWPOINTS HAVE MIXED OUT INTO THE 30S.          CONVECTION IS FORECAST TO EVOLVE/INTENSIFY FROM THE AFOREMENTIONED     MOUNTAIN RANGES AS FORCING FOR ASCENT INCREASES...WITH AN INCREASING     SVR THREAT AS WELL. STRONG MERIDIONAL FLOW IN ASSOCIATION WITH THE     TROUGH -- E.G. SAMPLED BY THE SALT LAKE CITY UT AND POCATELLO ID     SITES INDICATING 30-50 KT OF SLY FLOW WITHIN THE 2-4-KM-AGL LAYER --     WILL LIKELY BE MIXED TO THE SFC VIA CONVECTIVE MASS TRANSPORT     PROCESSES AS LOW-LEVEL LAPSE RATES CONTINUE TO STEEPEN WITH     SUBSTANTIAL DEWPOINT DEPRESSIONS. EFFECTIVE BULK SHEAR MAGNITUDES OF     40-50 KT WILL SUPPORT ORGANIZED STORM STRUCTURES INCLUDING LINE     SEGMENTS AND PERHAPS SOME SUPERCELLS...WHICH WILL LIKELY BE     ACCOMPANIED BY SVR WIND GUSTS. AND...WITH 7-8.5 C/KM LAPSE RATES     WITHIN THE 700-500-MB LAYER COMBINED WITH THE STRONG DEEP     SHEAR...SVR HAIL WILL BE OF CONCERN...PARTICULARLY WITH SUPERCELL     STRUCTURES.          ..COHEN/MEAD.. 06/05/2012               ATTN...WFO...BYZ...RIW...TFX...PIH...