Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 250936

Area Forecast Discussion
National Weather Service Portland OR
236 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 through today and 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)...The models continue to show
that a weak upper trough will be over the Pacific Northwest today and
Tuesday into early Wednesday under light westerly flow aloft as a
series of weak short waves move through. The main effect will be
continued onshore flow for night and morning low clouds clearing back
to near the coast in the afternoons.

After a day of less low clouds and more sunshine on Sunday that was
warmer than we had seen in a while, early this morning satellite
imagery showed deepening low clouds were solid along the coast and
were banked up against the west slopes of the coastal mountains as
they try to push inland. The low clouds were trying to shoot through
all the coastal gaps, including the Columbia River and the gaps
southwest and west of Eugene. Thus expect more coverage in both the
south and north valley areas this morning, clearing back to near the
coast in the afternoon, but probably not clearing offshore. The main
effect will be to drop temps in the inland valleys 5 to 7 degrees
today as compared to those Sunday. Expect some cooling at the coast
as well, where near the beaches it may be closer to 60 than 70. There
may also be some patchy drizzle this morning near the coast as well.

The pattern will not change much on Tuesday as the low clouds return
inland again later tonight and Tuesday morning. The models suggest
the low clouds will be more solid inland on Tuesday morning, with
more in the central Willamette Valley than expected today. This
should cause clearing to be a bit slower Tuesday than today, and drop
temperatures inland a couple of more degrees, near or perhaps a
couple of degrees below normal.

The low clouds will probably return inland on Wednesday morning but
be a little less extensive than on Tuesday as they favor the north
more than the south interior areas, then burn off a bit earlier. The
low level air mass is starting to warm a bit Wednesday afternoon as
the onshore flow starts to ease and the surface ridge axis shifts a
little north of the area, allowing temps to warm inland back into the
mid to upper 80s. Tolleson

.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.

.AVIATION...With a deepening marine layer tonight and more moisture
present, should see areas of MVFR ceilings inland late tonight
through about mid to late Monday morning then improving to VFR by
late morning. Expect coastal areas to mainly remain MVFR through the
TAF period.

KPDX AND APPROACHES...MVFR ceilings return Monday morning by about
14Z, clearing around 17Z or 18z. Bowen/TJ

.MARINE...There is a persistent summer-time weather pattern as high
pressure holds over the waters and low pressure remains over N CA and
S OR. The thermal trough over CA will expand north in the afternoons
and evenings for increased gusty winds. The winds have eased across
the waters so have dropped all advisories at this point. Models still
indicating very marginal small craft conditions Monday evening, but
will not issue an advisory at this point because it just doesn`t look
like winds will be consistent enough to warrant it. Seas remain very
choppy under the influence of very short period fresh swell, but
dominant periods are expected to lengthen late today to a more
comfortable 10-11 seconds. Winds look like they will strengthen
further starting late Tuesday afternoon through much of the rest of
the week. Seas are expected to come up a bit to 6-7 ft starting late
today, then remain in that range through at least Thursday. Could see
some higher seas towards the end of the week. Bowen/TJ




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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.