Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 310403
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
903 PM PDT Mon May 30 2016

.SYNOPSIS...An upper level ridge will persist over the Pacific
Northwest, bringing clearing skies and drying weather to
southwest Washington and northwest Oregon through Tuesday. The ridge
will produce warming temperatures over the next couple of days with
light offshore flow pushing inland temps close to 90 on Tuesday.
Onshore flow will start to develop Wednesday as a weak disturbance
approaches the region, with the remains of a surface front clipping
Southwest Washington. Another upper ridge builds over the region at
the end of the week.

&&

.UPDATE...Scattered to broken cirrus across the area. No significant
cloud cover means temps will cool down into the 40s to lower 50s
across most of the area. No changes to the forecast. Previous
discussion follows. -McCoy

.SHORT TERM...(Tonight through Thursday)...Latest visible satellite
imagery reveals cirrus continuing to spread across portions of the
area this afternoon, but otherwise mostly sunny skies along with
temperatures warming into the lower 70s with a few more degrees of
warming expected through the rest of the afternoon. Expect the upper
ridge to continue a slow shift eastward to the coast tonight and
inland over the Pacific NW by early Tuesday. Meanwhile, thermal low
pressure will continue to build up the coast, before pushing inland
later in the day Tuesday. With good offshore flow, abundant
sunshine, and 850 mb temperatures around 16-19 degrees C, expect a
very warm day across the region with temperatures well into the 70s
at the coast and into the upper 80s to perhaps around 90 in the
Willamette Valley. By late Tuesday evening or Tuesday night, models
suggest the thermal trough will move east towards the Cascades as
the flow aloft becomes more zonal. This will enable a decent push of
marine air into the coastal areas, and perhaps also along the lower
Columbia and into the northern Willamette Valley. As a result, have
increased cloud cover and decreased temperatures for Wednesday for
the coast.
Temperatures will also cool slightly inland, but with the air mass
remaining warm, temperatures will still remain in the 80s.
Temperatures cool a bit more on Thursday with more widespread clouds
expected as a weak front, or at least the remnants of one, brush the
northern portions of the region. Have retained and expanded slight
chance PoPs across the extreme northwestern portion of the forecast
area later Wednesday and Thursday, though some uncertainty in just
how much moisture will actually fall to the surface remains.

The upper ridge continues to advance inland Tuesday night and
Wednesday and flattens out a bit, and the low-level flow will turn
more onshore as the surface trough pushes east of the Cascades.
Expect low stratus or fog to return to the coast Tuesday night as the
cooler marine air returns. This should noticeably modify temperatures
Wednesday along the coast, but temperatures inland will remain well
above normal and only cool a few degrees. The remnants of a weak
shortwave passing well to the north could bring some light showers
across the far northern and coastal portions of the area late
Wednesday through Thursday. Heights continue to fall just a bit, but
expect temperatures to remain around 80 inland on Thursday.   /Cullen

.LONG TERM...(Thursday night through Sunday)...Good agreement
continues in the forecast models with respect to the end of the week
with a strong ridge developing over the southwestern U.S. Thursday
night and amplifying into the weekend. With 850 mb temperatures over
the area climbing to 18-22 degrees C, another stretch of warmth on
Friday and Saturday is expected. Given the latest trends, have
increased temperatures across the interior on Saturday and Sunday to
reflect the lower 90s Saturday and perhaps around 90 on Sunday. Of
note, a handful of record highs on Saturday are in the 89 to 91
degree range, so it is possible that new daily records could be set
at a few area stations. By later Sunday, the upper ridge migrates
eastward as an upper low over northern California begins to lift
north towards the region. With additional moisture pushed into the
region and decent instability, have expanded the chance of
thunderstorms, though still primarily restricted to the Cascades and
foothills.

&&

.AVIATION...Expect VFR conditions to continue through Tue evening.
Breezy northwesterly winds will diminish later this evening
through Tue morning, then become breezy again Tue afternoon and
evening.

PDX AND APPROACHES...VFR conditions expected through Tue night.
Breezy NW winds to subside overnight, then increase again Tue
afternoon and evening. Pyle

&&

.MARINE...A high pressure center is located off the Washington
coast while a thermally induced pressure trough over n Calif into
southern Oregon. This combination is leading to gusty winds along
Oregon marine waters. The gustier winds will become increasingly
confined to the outer waters overnight. Will keep a Small Craft
Advisory out through Tue evening for the outer waters. The
advisory for the inner waters will expire at 5 AM, but winds will
increase again Tue afternoon and evening, so another advisory will
likely be need. Winds weaken Tue night into Wed as high pressure
off the coast weakens and the thermal low shifts east of the
Oregon Cascades.

A similar thermal low setup will strengthen marine winds Saturday
through Monday with small craft strength winds likely. In
addition, expect this long duration northerly fetch to increase
seas to the 7 foot range. Given the primarily wind wave
dominated/fresh swell seas, expect relatively short periods could
bring square seas concerns during this period. Otherwise, seas
expected to remain between 3 and 6 feet through the remainder of
this week. Pyle/Bentley

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 11 PM PDT Tuesday for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 nm.

     Small Craft Advisory for winds until 5 AM PDT Tuesday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     10 nm.

&&


$$

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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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