FXUS66 KPQR 210339

Area Forecast Discussion
National Weather Service Portland OR
838 PM PDT Thu Jul 20 2017

.SYNOPSIS...Clouds will continue to dissipate across the area this
evening though a few may reform briefly late tonight and early
Friday. Otherwise high pressure will build in behind this system for
less clouds and warming temps Friday and Saturday. Strengthening
onshore flow is expected to bring a gradual cooling trend back to
near normal temps Monday and Tuesday. Longer range forecast models
hint at the potential for an upper trough with below normal temps
toward the middle of next week.

.SHORT TERM...Tonight through Sunday...After a few hundredths of an
inch of rain along the coast earlier today, and spotty light amounts
inland, skies were clearing this evening as the responsible system
was moving well east of our forecast area. The models indicate some
low clouds are possible late tonight and early Friday though they may
be overdone. Best chances could be near the coast and along the
Cascade foothills, but they may not be very solid. Some patchy fog is
possible also especially near the coast.

Otherwise sufficient higher pressure will build in for clearer skies
and warmer daytime temps. Temps will be around or just above normal
inland Friday, then close to 90 on Saturday. A system in the SE Gulf
of Alaska may give the north coast some clouds going into Saturday
but very little elsewhere.

Sunday will be an interesting day meteorologically as we will be in
between a passing system to our north across southern B.C. and a weak
low approaching the northern California coast. This will still be a
pretty warm day inland, and perhaps not bad at the coast as the
onshore flow may not increase until Sunday night and Monday. The low
to our south may get close enough for some late day thunder in our
southern Cascade forecast zones. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
Sunday night through Thursday...Models are starting to come into
better agreement in how to handle a weak upper low that is expected
to shear off from the tail end of today's cold front in the general
vicinity of 35N/135W, though there are still small differences in the
details. Both the GFS and ECMWF now show the upper low cutting off
west of the California coast and then lifting NE into Oregon by
Monday night. This will leave a slight chance of afternoon and
evening thunder Sunday and Monday for the Cascades south of around
Santiam Pass. Flow aloft generally remains S-SW ahead of the weak
upper low/trough, which should keep thunder chances limited to the
Cascade crest and points east. Troughing persists through the second
half of the week which will keep temperatures at or below normal.

.AVIATION...Expect VFR conditions to prevail over the interior
tonight and Fri. Over the coastal areas VFR conditions will
dominate through early tonight, but expect areas of IFR or low
end MVFR conditions to develop after 09z as some stratus and fog
develops, and continuing until midday Friday.

KPDX AND APPROACHES...VFR conditions tonight and Fri. The chance
for MVFR CIGs to redevelop Fri morning between 12z and 17z are
around 10 percent. Bowen

.MARINE...A ridge of high pres over the coastal waters will persist
into Sat. As a result, wind and sea conditions will remain benign
through Saturday. Northerly winds will increase with gusts into the
25 to 30 kt range Saturday night, and continue through Monday. Seas
will respond by building to 7 to 9 ft, with relatively short
periods, by late Sunday morning. Bowen




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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.
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