Damaging Wind in Washington, June 9, 2018

Area Forecast Discussion
National Weather Service Portland OR
309 PM PDT Sat Jun 9 2018

.SYNOPSIS...Showers and a few thunderstorms will continue through
this afternoon, with thunderstorms coming to an end this evening.
Snow levels will continue to fall overnight tonight, dropping to
around pass level Sunday morning (~4500 feet).	Only minor slushy
accumulations expected on the passes, with little to no impact to
travel through the Cascades. Otherwise, snow levels rise back up
through the day on Sunday as showers continue. High pressure builds
back early next week, bringing back drier and seasonably warmer
weather Monday and Tuesday. Another system may bring more showers
back midweek.

&&

.SHORT TERM...Today through Tuesday...Showers with a few
thunderstorms, mainly east of I-5 this afternoon.  Satellite shows
the deep, upper-level trough over the area.  With the base of the
trough swinging through this afternoon, the coolest air is moving
over the area aloft, steepening the lapse rates and destabilizing the
atmosphere.  This is what is causing the thunderstorms this
afternoon.  As we get later this evening, westerly flow kicks in
aloft, starting to gradually increase temperatures aloft.  This will
help to stabilize the airmass enough to bring an end to the
thunderstorm threat, though showers should continue though decrease
in coverage overnight.

By Sunday morning, due to overnight cooling and the cold air still in
place aloft, snow levels fall to around 4500 feet, which could mean
some slushy snow falling down on the passes, and perhaps 1-3 inches
of snow could fall above 4500 feet, with higher amounts up around
6000 ft or higher. This should not impact travel through the
Cascades, but hikers and campers planning trips up into the Cascades
above 4500 feet should be aware and prepared to encounter some snow
Sunday morning. Snow levels will be rising through the day on Sunday
as we get farther on the back side of this upper-level trough and a
ridge starts to build in. With this ridge building in, showers should
start to taper off late Sunday into early Monday.

This ridge will bring the return of seasonably warmer temperatures
and dry weather to the Pacific Northwest Monday and Tuesday.
-McCoy

.LONG TERM...Tuesday night through Saturday...The ridge that
dominates the early part of the week, moves out of the area on Tue
night. Wed a trough moves into the area. The 12z GFS and 12z Euro
while in disagreement on how deep the trough will be, both
agree that PoPs will increase for the middle of the week. The models
continue to diverge later in the week. The GFS is showing what looks
like a secondary trough swinging through around Thu morning. That
same time, the Euro has the leading edge of a ridge starting to build
over the eastern Pacific. Fri through Sat the GFS has the backside of
the trough hanging over the Cascades, as the ridge starts to build
along the Coast. The Euro Fri through Sat has this same ridge a bit
farther east. /42

&&

.AVIATION...Post frontal showers will continue through the next
24 hours. VFR conditions are expected to prevail with a mix of
MVFR at times. Scattered thunderstorms will continue to develop
across the Willamette Valley through this evening and could
produce brief IFR vis with +RA. If showers taper off tonight,
MVFR conditions become more likely, but right now it looks like
showers will stick around and VFR should prevail.

KPDX AND APPROACHES...VFR expected to prevail in post frontal shower
regime into Sunday. Occasional MVFR and possible brief IFR vis
with heavier showers or thunderstorms. Will see continuing
thunder chances through this evening, but hard to say if the
terminal or vicinity will be impacted. Could see some MVFR
overnight, but VFR seems more likely. Bowen

&&

.MARINE...Wind and seas remain below advisory criteria today and
tonight as a weak ridge of high pressure builds over the waters.
Seas have should remain around 6 ft through the weekend and drop
a foot or two early next week.

A surface low pressure system will approach the southern
Oregon/northern California coast Sunday, which is further south
than models previously showed it. As such, don't expect much
impact locally, but could see a brief period of southerly wind
gusts around 20 kt over the waters off the central Oregon coast. High
pressure begins to build Monday with no significant marine
concerns through midweek next week. Bowen

&&

.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.