MESO: Mesoscale Discussion 0637

ACUS11 KWNS 132035
SWOMCD
SPC MCD 132035
WAZ000-ORZ000-132230-

MESOSCALE DISCUSSION 0637
NWS STORM PREDICTION CENTER NORMAN OK
0335 PM CDT MON MAY 13 2013

AREAS AFFECTED...PORTIONS OF WRN WA AND FAR NWRN ORE

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 132035Z - 132230Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...THUNDERSTORMS MAY PRODUCE AN ISOLATED SVR WIND GUST OR TWO
THIS AFTERNOON...BUT THE ISSUANCE OF A WW IS NOT NEEDED.

DISCUSSION...THE LEADING EDGE OF STRONGER FORCING FOR ASCENT
PRECEDING AN APPROACHING PACIFIC SHORTWAVE TROUGH IS ADVANCING
INLAND OVER THE PACIFIC NW. SCATTERED THUNDERSTORMS HAVE DEVELOPED
ALONG A N/S-ORIENTED LINE ACROSS PARTS OF THE WILLAMETTE VALLEY TO
THE LOWER ELEVATIONS E OF PUGET SOUND. THIS IS IN RESPONSE TO THE
AFOREMENTIONED ASCENT HAVING OVERSPREAD AREAS OF MARGINAL
INSTABILITY -- I.E. MLCAPE OF 200-400 J/KG -- DRIVEN BY POCKETS OF
PRECEDING INSOLATION AMIDST UPPER 40S/LOWER 50S SFC DEWPOINTS.
UNIDIRECTIONAL FLOW THROUGH MUCH OF THE CLOUD-BEARING LAYER...WITH
AROUND 35 KT OF 0-6-KM BULK SHEAR...AND MODEST DIRECTIONAL LOW-LEVEL
SHEAR PER ATX VWP DATA MAY SUPPORT A FEW STRONGER QUASI-LINEAR
CONVECTIVE SEGMENTS. STRONG WIND GUSTS...WITH PERHAPS A MARGINALLY
SVR WIND GUST OR TWO...MAY ACCOMPANY THE MOST INTENSE STORMS.
HOWEVER...THE LIMITED DEGREE OF INSTABILITY/WEAK MID-LEVEL LAPSE
RATES SHOULD BE DETRIMENTAL IN SUPPORTING MORE ROBUST CONVECTIVE
UPDRAFTS. AS SUCH...ANY SVR THREAT SHOULD BE MARGINAL...BRIEF...AND
SPORADIC.

..COHEN/WEISS.. 05/13/2013

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

ATTN...WFO...PDT...SEW...PQR...

LAT...LON 46672279 48502248 48932216 48872106 47342131 45822184
45422224 45372277 45742298 46672279

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