Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 222209

Area Forecast Discussion
National Weather Service Portland OR
209 PM PST Wed Nov 22 2017

.SYNOPSIS...A series of fronts will continue periods of wet weather
into next week. Snow levels will remain above the Cascade passes
through Thursday morning. Snow levels will then lower to near the
Cascade passes Thursday afternoon and night, but the precipitation
will be light. There is a better chance for snow to impact the passes
Sunday and Monday.


.SHORT TERM...Today through Saturday..A front associated with a low
currently around 400 miles off of the Oregon coast will produce 1 to 2
inches of rain for the coast, coast range, and northern Cascades
tonight through Thursday night. The interior valleys including the
Willamette Valley can expect 0.5 to 0.75 inch of rain for the same
time period. Snow levels will remain high (at or above 8000 feet
through Thursday morning.  Snow levels will lower  down to near the
Cascade passes behind the front Thursday afternoon and evening as the
rain tapers off. There will be an increase of winds with the front
tonight and Thursday with 40 mph gusts possible along the coast and
higher terrain, and 30 mph gusts possible for the interior valleys.

A warm front passing by to the north will likely generate showers
along the coast and SW Washington Friday morning, but precipitable
water values lower considerably (~0.5 inch) and the rain totals
should be fairly light (<0.15 in). Areas away from the coast south of
Salem will be mostly dry late Friday morning into early Saturday

Another low will approach from the SW Friday night with a frontal
system producing rain across NW Oregon and SW Washington on Saturday.
Models are varying quite a bit on the strength and position of the
low, but are fairly consistent that it will generate rain over the
area.  The forecast for the strength and direction of the winds are
highly dependent on how the low plays out, and may vary the next few
forecast cycles as we get a better idea of how the low will track.
Snow levels will rise back to above 8000 feet late Saturday morning,
and do not have any winter weather concerns. Current rainfall
expectations from Saturday morning through Saturday night is between
0.5 to 0.75 inch. ~TJ

.LONG TERM...Saturday night through Wednesday...Snow levels will
lower down to the Cascade passes late Saturday night or early Sunday
morning behind a front. The front should move east of the Cascades
late Sunday morning, but will be followed by another front Sunday
night into Monday. A cold upper trough will help keep snow levels
down to near or just below the Cascade passes through Monday
evening. The models vary on when the Upper trough will move east, but
agree that an upper ridge will replace the upper trough by Tuesday.
This will favor increasing snow levels and decreasing rain chances
Tuesday and Wednesday. ~TJ


.AVIATION...A mix of VFR and MVFR at the coast and mostly VFR
inland this afternoon. As the cold front offshore slowly moves
toward the coast, rain will gradually increase this evening.
Expect cigs to lower to MVFR this evening as well with increasing
rain. Will see increasing southerly winds around midnight at the
coast, and early Thursday morning inland. Will likely continue to
see predominantly MVFR cigs through at least midday Thursday.

KPDX AND APPROACHES...Predominantly VFR through this evening,
with easterly winds 8 to 15 kt. Rain increasing this evening,
with cigs lowering to MVFR this evening around 03-06Z.
Predominantly MVFR cigs to continue through midday Thursday.


.MARINE...Expansive low pressure system offshore generating a
fairly good pressure gradient over the coastal waters today.
Already seeing wind gusts to 33 kt at our buoys, and will likely
see these winds increase to gusts to 35 to 38 kt later this
afternoon ahead of the cold front that will move across our
waters this evening. Models are bringing it in a sooner than
previously forecast, so shortened the gale warning, to end around
midnight tonight. Behind the front, winds will turn southwesterly
and ease back down to 20 to 30 kt. Will finally get a break from
the gales Thursday and Friday as we get a break in the active
weather pattern.

Seas generally 11 to 14 ft right now will build more into the
mid teens this afternoon as winds increase ahead of the front.
With increasing seas, expect choppy steep seas to continue.
Behind the front as winds start to ease, expect seas will subside
as well, gradually dropping through the day on Thursday. Seas
should drop below 10 ft by Thursday night and stay around 7 to 9
ft on Friday, apart from out near buoy 89 which may stay up
around 10 ft.

Lots of uncertainty surrounding the weather this weekend as
models keep shifting the track and intensity of the systems
moving through Saturday and Sunday. In any case, southerly gales
seem likely to return again Saturday into Sunday. -McCoy


.HYDROLOGY...The heavier rain over the S WA coastal mountains Tuesday
night resulted in the Grays River rising above flood stage. The river
is receding this afternoon, but additional moderate over the Willapa
hills expected tonight may keep the river above flood level through
Thursday morning. ~TJ

PZ...Gale Warning until midnight PST tonight for Coastal Waters from
     Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until
     midnight PST tonight.

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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.