MESOSCALE DISCUSSION 1854
   NWS STORM PREDICTION CENTER NORMAN OK
   0252 PM CDT SUN OCT 18 2015

   AREAS AFFECTED...PORTIONS OF SOUTHERN AND CENTRAL ARIZONA

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 181952Z - 182215Z

   PROBABILITY OF WATCH ISSUANCE...5 PERCENT

   SUMMARY...THERE WILL BE AN INCREASING POTENTIAL FOR STRONG
   THUNDERSTORM DEVELOPMENT DURING THE NEXT FEW HOURS...AND AN ISOLATED
   SVR TSTM OR TWO CANNOT BE RULED OUT. WW ISSUANCE IS NOT ANTICIPATED.

   DISCUSSION...VISIBLE SATELLITE LOOPS IMPLY AN INCREASE IN SHALLOW
   CONVECTIVE VIGOR WITH INCREASINGLY AGITATED CUMULUS FIELDS OVER THE
   SRN AZ HIGHER TERRAIN AND SURROUNDING DESERT FLOOR...FROM WHICH
   DEEPER CONVECTION IS BEGINNING TO ARISE IN PIMA COUNTY WEST OF
   TUCSON. WITH OVERALL TEMPORAL NEUTRALITY IN MIDLEVEL HEIGHT
   TENDENCIES THROUGH PRESENT...AND SOME POTENTIAL FOR HEIGHT FALLS TO
   OCCUR IN THE NEXT FEW HOURS WELL IN ADVANCE OF A WRN-CONUS
   TROUGH...CONVECTION SHOULD INCREASE IN COVERAGE AND INTENSITY DURING
   THE NEXT FEW HOURS -- CONTINUING INTO THE LATE AFTERNOON AND EARLY
   EVENING.

   MODEST LOW-LEVEL MOISTURE CONTINUES TO RESIDE S OF THE MOGOLLON
   RIM...WITH SFC DEWPOINTS IN THE 50S COMBINING WITH
   WIDESPREAD-INSOLATION-ENCOURAGED SFC HEATING TO RESULT IN MLCAPE ON
   THE ORDER OF 1000-1500 J/KG AND LITTLE MLCIN BASED ON THE MODIFIED
   12Z TUS RAOB AND FORECAST SOUNDINGS. FURTHERMORE...THE PHOENIX AND
   TUCSON VWPS ARE SAMPLING AROUND 20-30 KT OF FLOW IN THE 2-3-KM-AGL
   LAYER. GIVEN A MODEST INCREASE IN MIDLEVEL FLOW IN ASSOCIATION WITH
   THE HEIGHT FALLS FROM THE W...A FEW ORGANIZED/SUSTAINED TSTM
   STRUCTURES MAY ENSUE. STRONG WIND GUSTS -- AIDED BY 1000-1200 J/KG
   OF DCAPE -- AND SMALL HAIL WILL BE THE PRIMARY CONCERNS...AND AN
   ISOLATED SVR TSTM OR TWO MAY EVOLVE PARTICULARLY IF CONVECTION WERE
   TO BE SUSTAINED WHILE MIDLEVEL FLOW INCREASES INTO THE LATE
   AFTERNOON/EARLY EVENING. HOWEVER...WITH ONLY MODEST MIDLEVEL LAPSE
   RATES IN PLACE...AND GIVEN THE LIMITED NATURE OF LARGE-SCALE ASCENT
   AND LACK OF EVEN STRONGER DEEP SHEAR...CONFIDENCE IN A MORE
   SUBSTANTIAL SVR RISK IS NEGATED.

   ..COHEN/MEAD.. 10/18/2015


   ATTN...WFO...TWC...FGZ...PSR...

   LAT...LON   32001079 32571252 33301274 33811223 33681106 33400968
               32800921 32150950 32001079