Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251632
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
931 AM PDT Mon Jul 25 2016

.SYNOPSIS...A weak upper trough near the coast this morning 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. A stronger 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 next weekend.

&&

.SHORT TERM...(Today through Wednesday)...Visible satellite imagery
depicts widespread marine stratus along the coast and into the Coast
Range, with some intrusion through the coastal gaps into the southern
Willamette Valley, as well as along the Columbia River as far as
Portland. The stratus inland remains a rather shallow layer per
observations and model data, so expect relatively quick clearing
inland. However, the low clouds may persist a bit longer along the
coast where a modest onshore gradient will keep the clouds in place.
Some light drizzle may continue for the next few hours along the
North Oregon Coast; a few 0.01 inch measurements have been recorded
at Astoria and a handful of sites in the northern Coast Range and
Willapa Hills. Thus, expect a slightly cooler day at the coast than
yesterday; however, the sparse clouds inland will not do much to
prevent another warm day inland with afternoon highs well into the
mid 80s.

Clouds will be slower to return tonight, but expect marine stratus to
again push into the Coast Range. However, 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 the morning. A
weak shortwave passing across northwestern Washington should bring
heights a little lower. Some clouds will likely enter the northern
valley along the Columbia River, but less confidence in seeing a
cloudy start south of around Aurora and 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 will be rather shallow again and relatively quick to
dissipate. Flow turning more northerly may Heights will rise again,
with 500 mb heights rising to around 588 dam and 850 mb temperatures
climbing to around 16C. Onshore flow will wane as the surface ridge
axis shifts north and temperatures should again warm into the upper
80s across the interior.    Cullen

.LONG TERM...(Wednesday night through Sunday)...No changes. Previous
discussion follows. Models continue to show weak upper level ridging
over the Pac NW late next week. This will bring the typical pattern
of morning clouds and afternoon sun, with temps in the interior
rising into the mid 90s on Friday. Onshore flow looks to increase
next weekend as an upper level trough moves over the region. This
will bring more clouds to the interior and provide for a slight
cooling trend on Saturday and Sunday.

The threat of showers through the long term period remains near zero.
However, the GFS continues to show the potential for some monsoonal
moisture streaming north on Saturday. This could produce some
isolated dry thunderstorms in the Cascades, but confidence is low.
/64

&&

.AVIATION...IFR cigs will likely remain along the coast through
the day. Gusty winds along the coast this afternoon may improve
conditions to mvfr briefly, but there is low confidence for
coastal clearing or improvement. Stratus forming in the
Willamette Valley this morning will clear by 18z for VFR
conditions inland through the early evening. If the coast does
manage to clear this afternoon it will be brief as the marine
clouds will quickly return. 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 Tuesday morning.

KPDX AND APPROACHES...MVFR cigs will clear around 18z this morning
for 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 this afternoon and evening will likely
gust to around 25 kt for a brief period 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 N OR/S WA 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 very 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.
WA...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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