SPC MESOSCALE DISCUSSION 1899 FOR PORTIONS OF AZ...SRN UT
   CONCERNING...SEVERE THUNDERSTORM POTENTIAL...
   
   VALID 071501Z - 071800Z
   
   ONGOING ELEVATED CONVECTION OVER WRN AZ/SRN UT MAY BECOME SURFACE
   BASED BY EARLY AFTERNOON. BEFORE THEN...ISOLATED MARGINALLY SEVERE
   HAIL WILL BE POSSIBLE. HOWEVER...THE OVERALL SEVERE THREAT APPEARS
   TOO MINIMAL OVER THE NEXT SEVERAL HOURS TO REQUIRE WW ISSUANCE.
   
   ANALYSIS OF 12Z RAOB DATA SUGGESTS THAT CONVECTION OVER WRN AZ/FAR
   SWRN UT DEVELOPED IN REGION OF STRONG ASCENT AHEAD OF A VORTICITY
   CENTER OVER SRN CA AND WAS BASED AROUND 700 MB. RELATIVELY WEAK
   INSTABILITY /MUCAPE FROM 500 AND 1000 J/KG/ AND CLOUD BEARING SHEAR
   AROUND 40 KTS WOULD FAVOR SOME ROTATING UPDRAFTS AND THE POTENTIAL
   FOR SEVERE HAIL WITH THIS CONVECTION OVER THE NEXT SEVERAL HOURS.
   HOWEVER...RELATIVELY HIGH WBZ HEIGHTS /AROUND 12 KFT/ SUGGEST THAT
   THE OVERALL HAIL THREAT WILL REMAIN ISOLATED AND MARGINAL. RECENT
   VISIBLE SATELLITE IMAGERY/SURFACE ANALYSIS INDICATED A WELL DEFINED
   CLOUD LINE/BOUNDARY OVER FAR SWRN AZ. MODIFIED 12Z PHX/FLG
   SOUNDINGS SUGGESTS THAT SURFACE BASED CONVECTION WILL BE POSSIBLE
   ALONG THIS BOUNDARY AS IT MOVES EWD ONCE TEMPERATURES WARM INTO THE
   LOWER 90S. ADDITIONAL SURFACE BASED CONVECTIVE INITIATION MAY OCCUR
   OVER THE HIGHER TERRAIN OF CENTRAL AZ BY EARLY AFTERNOON...WHERE
   MODERATE SLY UPSLOPE FLOW WILL AID IN ENHANCED LOW LEVEL
   CONVERGENCE. AS LOW LEVEL LAPSE RATES/SURFACE BASED INSTABILITY
   INCREASE AND CONVECTION BECOMES ROOTED IN THE BOUNDARY LAYER...AN
   INCREASING SEVERE THREAT SHOULD OCCUR OVER CNTRL/ERN AZ AND SERN UT
   AFTER 07/18Z. 
   
   ..CROSBIE.. 09/07/02