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Mesoscale Discussion 666
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   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


   ATTN...WFO...BYZ...GGW...RIW...TFX...

   LAT...LON   44820908 45830928 46720928 47620930 48780912 48960883
               48960763 48730740 47910729 46750736 45750762 44910802
               44620886 44820908 

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Page last modified: May 21, 2016
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