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Area forecast discussion 
National Weather Service Portland or
232 PM PDT Mon Jul 25 2016

Synopsis...a weak upper trough near the coast with a weak westerly
flow aloft over the Pacific northwest will continue through Tuesday.
Expect morning low clouds giving way to afternoon sunshine and
seasonable afternoon temperatures. An upper level ridge will build
for the second half of the week and bring inland highs well into the
90s Thursday and Friday, before the next trough arrives to moderate
temperatures and increase clouds next weekend.

&&

Short term...(today through thursday)...another warm and sunny
afternoon underway across the Pacific northwest with most inland
sites already in the lower 80s. Visible satellite imagery reveals
the few exceptions to the clear skies are some of the coastal sites,
which continue to have some varying degree of lower clouds hanging
on. The general clearing will continue this evening inland, and
clouds will generally be slower to return tonight to the areas that
clear out. However, expect marine stratus to return to the coast late
this evening and push up against the Coast Range. The surface pattern
appears less favorable to enable a push through the central Coast
Range gaps, so have cut back sky cover for the South Valley for
Tuesday morning. A weak shortwave passing across northwestern
Washington should bring heights a little lower and some clouds will
likely enter the northern valley along the Columbia River. The chance
is lower but non-zero that some clouds make it south of Aurora or
McMinnville. For these northern locations, a slightly stronger
surface gradient may keep clouds in place a bit longer, but the South
Coast will lie south of the surface ridge axis and thus may be clear
relatively early in the morning. Temperatures may be somewhat cooler
Tuesday from Portland to Kelso and Cathlamet (only in the lower 80s)
as a result of these clouds, but persistence (mid 80s) looks like a
good forecast for the Salem to Eugene stretch of the valley.

For Wednesday, clouds will again be favored in the northern area, but
likely again will be rather shallow again and relatively quick to
dissipate. Flow turning more northerly may keep the central Oregon
coast largely clear or only briefly cloudy. Heights will rise again,
with 500 mb heights rising to around 588 dam and 850 mb temperatures
climbing to around 16c as a strong high over the southern Great Basin
and Desert Southwest builds north and west into the Pacific
northwest. Onshore flow will wane as the surface ridge axis shifts
north and temperatures should again warm into the upper 80s across
the interior. The ridge begins to flatten out with heights steady
over the region by Thursday, but the air mass continues to warm, so
expect temperatures around 90 for the inland locations. Some morning
clouds possible for the northern coastal areas and along the Columbia
River, but these should be rather minimal so very warm and abundant
sunshine will be the rule for Thursday. Cullen

Long term...(thursday night through monday)...by Thursday night and
Friday, the 850 mb temperatures will continue to nudge a bit warmer
with 588-590 dam 500 mb heights remaining over the region. With
little in the way of significant early clouds and a very warm air
mass, coupled with a relatively warm start (overnight lows 60-65 f
for the interior), Friday remains on track for the warmest day of the
week as temperatures rise into the mid 90s. Of note, while the 12z
deterministic GFS suggests cooler temperatures than some of the other
model guidance, it does lie on the extreme cool side of the gefs
envelope. However, there does remain some uncertainty in just how
warm temperatures will be on Friday. By Saturday, the next upper
trough drops from the Gulf of Alaska into northwestern Washington or
southern b.C., With the associated surface front sweeping across the
region by Saturday night or earlier Sunday. As a result, the
temperature forecast for the transition days - particularly, Saturday
- remains rather tricky. For now, will maintain Saturday in the upper
80s ahead of the front and Sunday in the upper 70s to around 80s with
additional clouds moving into the area. The deterministic GFS is
again the quickest to cool things off, but with the gefs ensemble
mean and particularly the European model (ecmwf) transitioning the pattern at a more
moderate pace, will continue to keep the forecast in this direction
for now. Regardless, very limited deep moisture with this system
means that pops were maintained generally 10 percent or less through
the weekend period. Cullen

&&

Aviation...clouds have cleared rapidly this afternoon with just a
few patches of MVFR cigs near the coast. Marine clouds will fill
in along the coast and make its way inland late this evening
through Tue morning. There will be less of a southerly marine
push tonight, and do not expect the south Willamette Valley to
have much if any stratus. Onshore winds and a weak trough north of
the area will favor a northerly push and expect stratus to impact
areas around the Columbia River and parts of the northern and
central Willamette Valley Tue morning.

Kpdx and approaches...VFR conditions through the early evening.
MVFR cigs will return around 7z tonight and persist through Tue
morning. Tj

&&

Marine...there will be little change the next several days as
north winds persist over the waters and wind waves remaining the
primary sea influence. The thermal trough will expand slightly
north in the afternoons and evenings for an increase in gusty
winds. The surface pressure gradient will be tightest south of
Cascade Head. The winds late this afternoon and evening will
likely gust to around 25 kt for the south waters and have issued
a short-lived Small Craft Advisory. The thermal trough will expand
further north Wed through Fri for a better chance of small craft
winds for the north or/S Washington waters in the afternoons and evenings.
Until then the best chance for gusty winds near or above 25 kt
will remain south of Cascade Head.

Seas remain choppy under the influence of short-period (4 to 5
second) wind waves. A fresh swell should develop today due to a
locally generated fetch from the persistent north winds and swell
periods should increase to 10 or 11 seconds. There is also a very
small (1 ft or less) long-period south swell that the buoys will
occasionally detect. Tj

&&

Pqr watches/warnings/advisories...
or...none.
Washington...none.
Pz...Small Craft Advisory for winds from 5 PM this afternoon to 11
PM PDT this evening for coastal waters from Cascade Head
or to Florence or out 60 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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