MESO: Mesoscale Discussion 1731

ACUS11 KWNS 161940
SWOMCD
SPC MCD 161940
IDZ000-ORZ000-WAZ000-162215-

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

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

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

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

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