ZCZC SPCSWOMCD ALL ACUS11 KWNS 212010 SPC MCD 212010 MTZ000-WYZ000-212115- MESOSCALE DISCUSSION 0666 NWS STORM PREDICTION CENTER NORMAN OK 0310 PM CDT SAT MAY 21 2016 AREAS AFFECTED...CENTRAL MT...FAR NRN WY CONCERNING...SEVERE POTENTIAL...WATCH LIKELY VALID 212010Z - 212115Z PROBABILITY OF WATCH ISSUANCE...80 PERCENT SUMMARY...INTENSE THUNDERSTORM DEVELOPMENT IS POSSIBLE LATER THIS AFTERNOON WITH A THREAT FOR LARGE HAIL...DAMAGING WIND...AND A TORNADO OR TWO. WATCH ISSUANCE WILL LIKELY BE REQUIRED SOON. DISCUSSION...AT 20Z...CONVECTION IS ONGOING ON THE COLD SIDE OF A NEARLY STATIONARY SFC BOUNDARY DRAPED FROM NWRN WY INTO CENTRAL MT. A 998 MB SFC LOW IS LOCATED ON THE BOUNDARY ACROSS NWRN WY NEAR CODY...WITH A WELL-DEFINED RISE-FALL COUPLET NOTED IN CONJUNCTION WITH THE LOW. STRONG LOW-LEVEL SLY FLOW IS NOTED IN SFC OBS AND IN THE RIW/BLX VWPS...WITH WIND GUSTS IN EXCESS OF 50 KTS NOTED AT TBX AWAY FROM ANY CONVECTION. RELATIVELY STRONG HEATING IS UNDERWAY TO THE EAST OF THE SFC BOUNDARY...WITH MID/UPPER 50S DEWPOINTS NOTED ACROSS MUCH OF CNTRL/ERN MT. WHILE SOME MIXING/DRYING IS EXPECTED IN THE WARM SECTOR THIS AFTERNOON...STEEP MIDLEVEL LAPSE RATES WILL SUPPORT MODERATE INSTABILITY...WITH SBCAPE OF 1000-1500 J/KG ALREADY NOTED IN RECENT MESOANALYSIS ON THE WARM SIDE OF THE BOUNDARY. AS THE LOW PRESSURE MOVES NNEWD ALONG THE BOUNDARY...SFC-BASED STORM INITIATION WILL BE POSSIBLE. EFFECTIVE SHEAR OF 50-70 KTS UNDERNEATH VERY STRONG MIDLEVEL FLOW WILL BE MORE THAN SUFFICIENT FOR ORGANIZED STORM STRUCTURES. RECENT CAM GUIDANCE INDICATES THE POTENTIAL FOR AT LEAST A COUPLE OF SUPERCELLS MOVING NNEWD ALONG THE BOUNDARY...WHICH WOULD HAVE THE POTENTIAL FOR LARGE HAIL AND DAMAGING WIND. SOME TORNADO THREAT WILL ALSO EXIST GIVEN RELATIVELY STRONG LOW-LEVEL SHEAR AND THE POTENTIAL FOR BOUNDARY INTERACTION...THOUGH THE COLD NATURE OF THE AIRMASS WEST OF THE FRONT MAY TEMPER THIS THREAT TO SOME EXTENT. SOME POTENTIAL ALSO EXISTS FOR EVENTUAL UPSCALE GROWTH INTO BOWING LINE SEGMENTS WITH A GREATER THREAT FOR DAMAGING WIND. ..DEAN/HART.. 05/21/2016 ...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT... ATTN...WFO...BYZ...GGW...RIW...TFX... LAT...LON 44820908 45830928 46720928 47620930 48780912 48960883 48960763 48730740 47910729 46750736 45750762 44910802 44620886 44820908 NNNN