MESOSCALE DISCUSSION 1731
   NWS STORM PREDICTION CENTER NORMAN OK
   0240 PM CDT FRI AUG 16 2013

   AREAS AFFECTED...PORTIONS OF CNTRL/NRN ORE AND SRN WA...A SMALL PART
   OF WRN ID

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 161940Z - 162215Z

   PROBABILITY OF WATCH ISSUANCE...20 PERCENT

   SUMMARY...THERE WILL EXIST AN ISOLATED SEVERE THUNDERSTORM POTENTIAL
   INTO THE EVENING HOURS...THOUGH LIMITED COVERAGE OF SUCH POTENTIAL
   IS CURRENTLY EXPECTED TO PRECLUDE WW ISSUANCE.

   DISCUSSION...THE PRESENCE OF ANY SALIENT MECHANISMS FORCING DEEP
   ASCENT WITHIN A BROAD SW/NE-ORIENTED MOIST PLUME DOWNSTREAM OF AN
   E-PACIFIC TROUGH ARE RATHER AMBIGUOUS PER RECENT WATER VAPOR LOOPS.
   REGARDLESS...RELATIVELY ENHANCED TROPOSPHERIC MOISTURE CONTENT
   WITHIN THIS PLUME -- CHARACTERIZED BY GPS PW VALUES AROUND 0.8-1.2
   INCHES -- OVERLIES THE AREA...AND SFC OBS INDICATE DEWPOINTS ONLY
   HAVING MIXED OUT INTO THE UPPER 40S TO THE MIDDLE 50S. DIURNAL
   HEATING IS PROMOTING BOTH AN INCREASE IN SFC-BASED BUOYANCY AMIDST
   THIS MOISTURE...ALONG WITH DEEPENING/STRENGTHENING OROGRAPHIC
   CIRCULATIONS.

   CUMULUS DEVELOPMENT HAS BEEN NOTED INVOF THE CASCADES AND ENEWD OVER
   THE HIGHER ELEVATIONS TOWARD THE COLUMBIA PLATEAU. PRESENT
   INDICATIONS ARE THAT TROPOSPHERIC MOISTURE WILL BE SUFFICIENTLY
   ADEQUATE IN THE PRESENCE OF MLCAPE OF AROUND 300-1000 J/KG FOR
   ISOLATED THUNDERSTORMS TO EVOLVE FROM THIS INITIAL CONVECTIVE
   DEVELOPMENT DURING THE NEXT FEW HOURS.

   AROUND 25-40 KT OF SSWLY/SWLY MID-LEVEL FLOW WERE SAMPLED BY THE
   MEDFORD AND SALEM ORE 12Z RAOBS...AND SIMILAR MAGNITUDES WILL LIKELY
   REMAIN PRESENT INTO THE EVENING OWING TO LITTLE OVERALL CHANGE IN
   THE MID-LEVEL HEIGHT GRADIENT. CORRESPONDING MODERATE DEEP SHEAR MAY
   SUPPORT ONE OR TWO ORGANIZED STORM STRUCTURES/POSSIBLE SUPERCELLS
   INTO THE EVENING HOURS. SVR HAIL/WIND MAY OCCUR WITH THE MOST
   INTENSE STORMS. HOWEVER...THE LACK OF STRONGER FORCING FOR ASCENT
   WILL LIKELY MITIGATE THE COVERAGE OF THE SVR POTENTIAL. WHILE TRENDS
   WILL BE MONITORED...THE ISSUANCE OF A WW IS CURRENTLY UNLIKELY.

   ..COHEN/KERR.. 08/16/2013


   ATTN...WFO...MSO...BOI...OTX...PDT...MFR...

   LAT...LON   46721611 45601670 43471980 42702197 43532188 45272132
               46282040 47211826 47361662 46721611