Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 212041
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
140 PM PDT Thu Sep 21 2017

.SYNOPSIS...Much more tranquil today, even though still have a few
showers around through this evening. High pressure builds in over the
weekend and continues into early next week for some great late
September weather in store for the region, with cool nights with
patchy fog and mild mostly sunny days.

&&

.SHORT TERM...Today through Sunday...The upper level trough that
brought all this rain over the past several days is finally moving
off to the east, with the trough axis now over eastern Oregon. On the
back side of the trough, we are seeing northerly flow over western
Oregon and Washington, maintaining some threat for showers, mainly
over the Cascades and Coast Range. We are seeing this materialize
this afternoon, as showers are now starting to pop up. Showers should
wind down around sunset tonight, with maybe a stray shower or two
hanging around over the Cascade Crest overnight.

With the cool air mass and light winds tonight, we will see good
conditions for fog. With high pressure starting to build over the
area tonight, this will bring an end to the showers and clear skies
across the area. This will allow more extensive fog to develop
tonight, persisting into Friday morning. Expect pockets of denser fog
to develop as well, with visibilities possibly around 1/4 mile or
less. Motorists should be prepared to slow down tonight and Friday
morning. A cool night and extensive fog will give way to milder
daytime temperatures, with temps mostly around 60 along the coast and
in the mid 60s inland on Friday.

Not much change on Saturday and Sunday, as we maintain light winds
with high pressure over the region. Expect nighttime/morning fog, and
cool nights and mild days, though temps will be gradually getting
warmer over the weekend. -McCoy

.LONG TERM...Sunday night through Friday...High pressure continuing
build into the area. Snow levels will continue to rise as the week
progresses. Temperatures will also start warming back up near normal
during the week. -Bishop

&&

.AVIATION...The chances for showers decrease through tonight.
MVFR cigs are hanging around longer than expected this afternoon.
Satellite imagery shows clearing skies and drier air approaching
from the north, and think there will be mostly VFR conditions
early this evening. Any clearing will result in low stratus or
radiation fog late tonight into Saturday morning with MVFR or
IFR conditions likely late tonight into Saturday morning.

KPDX AND APPROACHES...A stray shower is possible late this
afternoon and early this evening, but the chances are dwindling.
Mostly VFR conditions expected this evening. Winds will remain
light through Saturday morning. Any clearing tonight will
provide the possibility for radiation fog and MVFR or IFR
conditions early Saturday morning. ~TJ

&&

.MARINE...No changes and previous discussion follows...A series
of lows off of the B.C. coast will maintain 8 to 9 ft NW seas for
the Washington and Oregon waters through tonight. The seas
should subside to below 6 ft Saturday morning with slight changes
in the swell direction (northwest to west) into next week.

The winds will be light and variable today as a weak low moves
north to south across the waters. Building high pressure will
return light (less than 15 kt) north-northwest winds tonight
through early next week. However, weak lows moving north of the
waters will result in light and variable winds at times, mainly
north of Cascade Head. The first period of these light winds will
be late Friday morning into early Friday afternoon, with another
one Friday night through Saturday. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for Rough Columbia River Bar from 5 PM
     this afternoon to 9 PM PDT this evening.

&&

$$


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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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