Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 250939
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
239 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 over the higher North Oregon and South
Washington Cascades. High pressure will return 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...A broad upper level trough
moved through the Pac NW Wednesday and is now east of the Rockies.
However, a shortwave on the backside of the trough is diving south
through the Pac NW and will continue to influence our weather today.

Onshore flow continues this morning, although not nearly as strong as
we experienced yesterday. Satellite imagery shows scattered clouds
around the area with little pattern. Still think it`s possible clouds
will backbuild from the Cascade foothills into at least the northern
Willamette Valley this morning, but clouds should clear by late this
morning.

Although the main upper low will move east into the northern Great
Plains Thu, the elongated trough axis on the backside of the low will
pinch off and hang back over the Pac NW. The GFS shows channeled 500
mb vorticity through the interior valleys of Washington and Northern
Oregon today in north flow aloft. The GFS, NAM, and ECMWF all hint at
some light QPF this afternoon, primarily over the S Washington
Cascades and N Oregon Cascades. The GFS continues to have surface
based LI values of -2 to -3 C from around Mt. Hood northward in the
afternoon, so left the slight chance of thunderstorms in the fcst
near the Cascade crest. 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 inland

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...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...Satellite imagery indicates a fairly decent shield
of stratocumulus across southwest Washington and northwest Oregon
early this morning, with some holes in the clouds noted. Cigs
are VFR except some MVFR along the coast. The clouds may tend to
fill in a bit more this morning. Expect clouds to break up west
of the Cascades this afternoon though some scattered clouds may
persist a while in the afternoon. The Cascades will likely see
some showers or thunderstorms develop and spread north to south
this afternoon and evening. Conditions tonight will be mostly
VFR, with any fog or low clouds inland patchy and forming late.
Along the coast there could be a little low stratus and fog later
tonight with local IFR conditions.

KPDX AND APPROACHES...VFR conditions today, with occasional VFR
cigs this morning. VFR conditions continuing tonight. pt

&&

.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

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
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 until 8 AM
     PDT this morning.

     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.



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