Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251629

Area Forecast Discussion
National Weather Service Portland OR
927 AM PDT Thu May 25 2017

.SYNOPSIS...An upper level trough will reside over the Pacific
Northwest through Thursday. There remains a slim threat of late day
thunderstorms Thursday near the crest of the North Oregon and South
Washington Cascades. High pressure returns Friday for drier,
sunnier, and warmer weather. Warm and dry conditions continue through
the holiday weekend and early next week. There is a slim threat of
late-afternoon and evening thunderstorms over the higher Cascades
Monday through Wednesday.


.SHORT TERM...Today through Saturday...Only a few minor adjustments
to sky cover portion of the forecast this morning to better reflect
trends. Some pockets of lower clouds remain in the valleys northern
Cascade foothills, along the Long Beach Peninsula south to Youngs
Bay, around the Portland metro area, and south of Eugene. Otherwise,
skies largely remain clear this morning and the locations still in
clouds will see gradually clearing skies by late this morning. Have
maintained a slight chance of an afternoon thunderstorm near the
crest of the Cascades from about Mt. Hood northward. Models continue
to indicate a decent amount of instability, but somewhat limited
moisture so confidence remains on the lower side that coverage will
be anything other than extremely isolated.  Remainder of previous
discussion remains valid and follows below.   Cullen

Models are in agreement with 850 mb temps warming to around 9-10 deg
C this afternoon, which is a little bit warmer than previous runs, so
warmed high temperatures a degree or two. Models keep inland areas
generally clear tonight into Friday morning with some clouds along
the coast. With an additional 3 to 5 deg C of warming at 850 mb
Friday, expect temperatures to continue to warm, likely into the 80s

Models continue to suggest a south stratus surge up the coast
beginning Fri evening and continuing into Sat morning, which will
keep temperatures along the coast, particularly south of about
Tillamook, cooler during the day Saturday. Outside of the stratus
surge, temperatures will warm another few degrees with the upper
ridge axis overhead, and potentially into the mid 80s in some inland
areas. Bowen

.LONG TERM...No Changes. Previous discussion follows...Saturday night
through Wednesday. The models are in general agreement through about
Mon or Mon night with an upper ridge dominating the weather and
keeping surface conditions warm and dry. Will see above-normal
daytime temperatures potentially approaching 90 degrees again inland
Sun and Memorial Day. Removed thunder from the Cascade crest Sunday
afternoon as models are backing off on instability. However, kept
thunder threat Mon with better instability and model QPF showing
indications of a convective pattern.

Models start to diverge Mon night and Tue. The GFS shows a short-wave
disturbance reaching the area Tue, which would bring a deeper marine
layer and result in a more stable air mass. But the ECMWF holds the
500 mb ridge axis over the area Tue, for a continued slim threat of
Cascade thunderstorms. Kept the threat of thunderstorms south of Mt.
Jefferson Tue as the ECMWF seems to have done better recently with
the timing of the ridge breaking down. By Wednesday, both the GFS and
ECMWF show the ridge axis over the Rockies and locally south to
southwesterly 500 mb flow, which may support more thunder along the
Cascade crest, so added a slight chance of thunder Wednesday
afternoon and evening, mainly from about Mt. Jefferson south. Bowen


.AVIATION...Stratocumulus deck is beginning to thin out over the
north Willamette Valley and VFR conditions should prevail by 17Z
or 18Z at most TAF sites.  The Cascades will likely see some
showers or thunderstorms develop and spread north to south this
afternoon and evening but should miss all TAF sites. Conditions
tonight will be mostly VFR, with any fog or low clouds inland
patchy and forming late. Along the coast there could be some low
stratus and fog later tonight with local IFR conditions.

KPDX AND APPROACHES...MVFR cigs lift to VFR in the next hour or
two and VFR conditions will remain through the period. /Bentley


.MARINE...Winds have eased below Small Craft Advisory thresholds
early this morning and will decrease more this morning. The
pattern of higher pressure over the NE Pacific and lower
pressure inland will persist into early next week, and winds
should stay below Small Craft Advisory thresholds through that
time period. Next modest front looks to be around the middle of
next week at the earliest.

Steep, choppy seas continue to run 1-2 ft above model guidance
early this morning, and thus don`t expect seas to drop below and
stay below 10 ft until later today. Have extended the Small Craft
Advisory for Hazardous Seas as a result. Seas then stay below 10
ft for at least the next week. pt


PZ...Small Craft Advisory for hazardous seas until 3 PM PDT this
     afternoon for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 4 PM
     this afternoon to 7 PM PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 4 AM to
     8 AM PDT Friday.



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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.