MESOSCALE DISCUSSION 1218
   NWS STORM PREDICTION CENTER NORMAN OK
   0302 PM CDT WED JUN 20 2007
   
   AREAS AFFECTED...PORTIONS OF CNTRL ID...SWRN MT
   
   CONCERNING...SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY 
   
   VALID 202002Z - 202100Z
   
   CLUSTERS OF STRONG TO SEVERE TSTMS ARE EXPECTED TO DEVELOP THIS
   AFTERNOON IN ASSOCIATION WITH A MID-LEVEL IMPULSE IMPINGING UPON THE
   WRN CONUS RIDGE. ALTHOUGH INSTABILITY SHOULD REMAIN MODEST...STRONG
   DEEP-LAYER SHEAR SHOULD RESULT IN SOME SUPERCELLS WITH LARGE HAIL
   AND GUSTY OUTFLOW WINDS AS THE PRIMARY THREATS. A SEVERE TSTM WATCH
   ISSUANCE IS LIKELY BY 21Z.
   
   A MID-LEVEL IMPULSE /EVIDENT IN WATER VAPOR IMAGERY/ HAS NOW REACHED
   THE NRN GREAT BASIN. 12Z MODEL GUIDANCE RESOLVED THIS FEATURE QUITE
   WELL AND TRACK IT ATOP THE WRN CONUS RIDGE AXIS TOWARDS THE NRN
   ROCKIES BY THIS EVENING. LIFT ASSOCIATED WITH THIS IMPULSE HAS AIDED
   IN SMALL CB/TCU DEVELOPMENT ACROSS THE ID SAWTOOTHS AND MT SWRN MTNS
   /PER RECENT VISIBLE SATELLITE AND LIGHTNING IMAGERY/. LATEST RUC
   OBJECTIVE ANALYSIS INDICATES MODEST SURFACE-BASED INSTABILITY WITH
   SBCAPES APPROACHING 1000 J/KG. THIS IN COMBINATION WITH 30 TO 40 KTS
   OF SWLY MID-LEVEL FLOW WILL SUPPORT SUPERCELL DEVELOPMENT. IN
   ADDITION TO A LARGE HAIL THREAT...STEEP LOW-LEVEL LAPSE RATES WILL
   AID IN GUSTY DOWNDRAFT WINDS.
   
   ..GRAMS.. 06/20/2007
   
   
   ATTN...WFO...BYZ...RIW...TFX...PIH...MSO...BOI...
   
   46311540 47011470 47281352 47141184 46441074 45101058
   44371274 44191344 44471439 45111539