Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 240346 AAA

Area Forecast Discussion
National Weather Service Portland OR
846 PM PDT Mon Apr 23 2018

Updated Aviation section

.SYNOPSIS...High pressure over the region will bring lots of
sun and warm temps to much of the region through mid week. Cooling
along the coast begins Wed, and spreads inland Thu and Fri. An upper
level low approaching the north CA coast late in the week will
spread a chance for showers and maybe even a few thunderstorms to
the region late Thu and Thu night. Low pres will stick around
through the weekend keeping chances for showers going along with
seasonably cool temps.


.SHORT TERM...Tonight through Thursday...An upper level ridge seen
in water vapor pictures Mon afternoon along 130W, will move inland
over the Pacific NW tonight, then linger through Wed. With a thermal
induced trough along the coast, most inland areas will see an
offshore flow that will help to keep skies mostly clear through Wed.
Models indicating 850 mb temps continue to warm Tue and Wed, reaching
close to 15C by Wed, which should be good for highs into the lower
80s inland valleys, and which may also challenge some of our high
temp records. Along the coast onshore flow appears likely to develop
late Tue, then again Wed as the surface trough begins to shift
onshore. The turn to onshore flow, earliest along the central OR
coast, will cut off the diurnal temp rise along the coast earlier
each day.

By Thu models develop a sse flow over the region as a large upper
level low approaches the north CA coast. As the upper heights begin
to come down and the surface trough moves inland, a developing
onshore flow will begin to bring temps down over the interior as
early as Thu, although some areas may not see much cooling Thu. The
se flow and some diffluence aloft may begin to destabilize the
atmosphere enough Thu afternoon to introduce a slight chance for
thunderstorms to the Lane County Cascades.

.LONG TERM...Thursday night through Monday...While models agree on
the upper low off the north CA and south OR coast eventually moving
inland, models diverge some on how quickly that happens, and what
happens afterwards at the end of the weekend. As the low level flow
likely remains onshore through the extended period, the differing
models wind up yielding nearly the same forecast; a chance for
showers each day with temps near seasonal normals.


.AVIATION...06z TAFs: VFR conditions expected tonight and
Tuesday. Offshore flow will continue through early Tuesday before
easing Tuesday afternoon.

KPDX AND APPROACHES...VFR conditions through Tuesday. Fairly
strong easterly wind gusts of 20-30 kt will continue through
18z-20z Tuesday, then ease off.


.MARINE...Surface thermal trough along the coast will drift
offshore tonight. This will result in winds becoming increasingly
offshore with wind gusts of 15 to 20 kts. Some isolated gusts
near 25 kts possible downwind of the coastal river gaps
including the mouth of the Columbia River tonight.

A longer period westerly swell arrives later tonight into
Tuesday, but wave heights remain below 10 ft. During the latter
half of the week, a southerly wind reversal may develop along the
coast bringing some fog and low clouds. Seas likely will remain
below 10 ft. Small craft advisory level winds could return
towards the weekend, as a front moves into the north Oregon and
south Washington waters. /tw



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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 CWA or forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.