Area Forecast Discussion
Issued by NWS Portland, OR

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147
FXUS66 KPQR 191618
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
918 AM PDT Thu Apr 19 2018

Updated Aviation and Marine sections.

.SYNOPSIS...Dry and mild weather is expected today and Friday. A weak
frontal system will move across the region Friday night and Saturday
for light rain and Cascade snow. Dry and mild weather returns Sunday
and Monday.

&&

.SHORT TERM...Today through Sunday...Showers wrapping around an upper
low over Southern California are approaching the Oregon Cascades from
the east early this morning. Radar imagery shows these showers are
dissipating quickly once they reach the Cascades, and rainfall
measurements have been very unimpressive over the Cascades so have
decreased Pops.

An upper level ridge builds over the Pacific NW today and holds
through Friday for dry weather, mostly sunny skies, and warming
temperatures. Some high clouds will likely move over the region late
tonight and Friday as a frontal system approaches the coast.

A warm front will move well north of the area and have little impact
Friday morning, but the cold front will bring a chance of rain Friday
evening through Saturday morning with showers possibly lingering
across extreme SW Washington Saturday afternoon. The snow levels will
remain above the Cascade passes most of Friday then lower to around
3500 feet Saturday morning as the rain decreases and turns to
showers.  Rain and Cascade snow will be on the light side with the
highest 24 hour (Fri afternoon-Sat afternoon) totals around 0.20
inch along the north coast, north coastal mountains, and the south
Washington Cascades. The greatest chances for precipitation will be
along the coast late Friday night and over the Ces, and rainfall
measurements have been very unimpressive over ascades Saturday
morning. The Willamette Valley, especially south of Salem may not
see much if any rain.

Showers will end Saturday night for a dry Sunday. Dry weather is
expected Sunday with surface high pressure over the area and
low-level offshore winds. However a shortwave upper trough moving
over the area will likely keep some clouds around, and limit heating.
Inland temperatures will be around around 5 degrees above seasonal
normal (mid 60s) this weekend. ~TJ

.LONG TERM...Sunday night through Wednesday...An upper ridge
amplifies on Monday continuing dry weather, and raising temperatures
to near or slightly above 70, possibly resulting in the warmest
weather of the year so far. A weakening front approaches Monday night
with increasing clouds Tuesday morning, and slightly cooler
temperatures Tuesday afternoon. An upper level trough may generate
showers over the Oregon Cascades Tuesday afternoon with snow levels
well above the Cascade passes. The forecast for Wednesday is less
certain as the models diverge on the position of an upper trough near
the region. THe GFS brings the trough over the area for cloudier,
cooler and showery weather whereas the ECMWF forecasts the trough
will stay further offshore and the weather in NW Oregon will be dry
and warm. Have leaned towards the ECMWF since model verification
shows that it generally out performs the GFS in long term
forecasting. ~TJ

&&

.AVIATION...High pressure is bringing light winds and mainly
clear conditions to the majority of the forecast area this
morning. That said, there is a bit of fog in some valleys,
including in and around KEUG. This fog is fairly shallow and
should burn off by 18z. Otherwise, aside from the morning valley
fog and a few cumulus buildups and perhaps a shower or two over
the Cascade crest, VFR conditions should prevail through this
evening.

KPDX AND APPROACHES...VFR with light W-NW flow through this
evening.  Weagle

&&

.MARINE...High pressure will remain across the waters through
Friday, then give way to an approaching cold front Friday night.
Expect low-end Small Craft Advisory winds and seas associated
with this system Friday night and Saturday morning...mainly
across the northern waters. The front will be a fast mover, and
high pressure will already be rebuilding across the waters
Saturday. High pressure will then dominate the Pac NW and
adjacent waters through at least Monday. However, thermal low
pressure building up the Oregon Coast from NW California will
bring increasing northerlies to the Oregon waters Sunday and
Monday.  Weagle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

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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.



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