MESOSCALE DISCUSSION 1476, AREAS AFFECTED...PORTIONS NRN SD...SRN ND...EXTREME SERN MT...EXTREME NERN WY. CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

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MESOSCALE DISCUSSION 1476 NWS STORM PREDICTION CENTER NORMAN OK 0307 PM CDT MON JUL 16 2012 AREAS AFFECTED...PORTIONS NRN SD...SRN ND...EXTREME SERN MT...EXTREME NERN WY. CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 162007Z - 162200Z PROBABILITY OF WATCH ISSUANCE...40 PERCENT SUMMARY...SVR POTENTIAL INCREASING IN CORRIDOR FROM NWRN SD/EXTREME SERN MT DOWNSHEAR ACROSS SD/ND BORDER REGION THROUGH REMAINDER AFTERNOON. DAMAGING GUSTS AND OCNL HAIL ARE POSSIBLE. 20Z CONVECTIVE OUTLOOK HAS BEEN UPGRADED CATEGORICALLY FOR THIS REGIME. DISCUSSION...SFC MESOANALYSIS SHOWED PRIMARY LOW OVER CENTRAL SD NEAR PIR...ALONG QUASISTATIONARY FRONT EXTENDING NEWD BETWEEN ABR-ATY AND WSWWD OVER NRN RIM OF BLACK HILLS. SECONDARY LOW-LEVEL CIRCULATION WAS EVIDENT IN REFLECTIVITY IMAGERY NEAR STURGIS SD...WITH BOUNDARY EXTENDING NWWD ACROSS DEVILS TOWER AREA OF WY TO SWRN CARTER COUNTY SD. VIS IMAGERY SHOWS INCREASING COVERAGE/DEPTH OF CONVECTIVE ELEMENTS ALONG AND E OF BOUNDARY FROM SERN MT TO BLACK HILLS...AND OTHER CONVECTION DEEPENING OVER BIGHORNS FARTHER WSW. ENHANCED LOW-LEVEL ELY/NELY FLOW OVER W-CENTRAL/NWRN SD...AROUND NRN PORTION OF SECONDARY CYCLONE...SHOULD CONTRIBUTE BOTH LOW-LEVEL THETAE ADVECTION AND ENHANCEMENT TO STORM-RELATIVE INFLOW FOR ANY SUSTAINED CONVECTION MOVING OFF BLACK HILLS OR WRN SEGMENT OF BOUNDARY. LAPSE RATES ALOFT ARE NOT PARTICULARLY STG...PER MORNING UNR RAOB AND MODIFIED MODEL SOUNDINGS. HOWEVER...PROGRESSIVELY HIGHER THETAE WITH EWD EXTENT N OF BOUNDARY WILL CONTRIBUTE TO MLCAPE RANGING FROM AROUND 1000 J/KG OVER NERN WY TO 3500 J/KG ALONG CENTRAL-ERN PORTIONS ND/SD BORDER WHERE SFC MOISTURE IS GREATEST. WELL-MIXED SUBCLOUD LAYERS WILL SUPPORT STG-SVR GUST THREAT...AND RISK OF LARGE HAIL WILL BE ENHANCED IN ANY SUPERCELLS. 40-50 KT EFFECTIVE SHEAR MAGNITUDES ARE EVIDENT OVER THIS CORRIDOR IN SUPPORT OF SUPERCELL POTENTIAL. ..EDWARDS/CARBIN.. 07/16/2012 ATTN...WFO...ABR...BIS...UNR...BYZ... LAT...LON 44640190 44400358 44450443 44870592 45790489 46230377 46650125 46680054 46529951 45609893 44739999 44480118 44640190