Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 162302

Area Forecast Discussion
National Weather Service Portland OR
301 PM PST Sat Dec 16 2017

.SYNOPSIS...Cool cloudy weather will continue into Monday. Light rain
and Cascade snow is expected, but mainly north of a Tillamook to
Mt Hood line. Snow levels will rise to near or slightly above the
Cascade passes Sunday afternoon. Rain and Cascade snow becomes more
widespread Tuesday and Wednesday as a cold front moves across the
area. Dry and cold weather is expected after Wednesday.


.SHORT TERM...Today through Tuesday...Most areas will be dry this
afternoon and evening with the best chance for light rain across
extreme SW Washington. A warm front is approaching Washington State
this afternoon and will bring increased chances for precipitation
(mostly north of Salem) late tonight through Sunday. Snow levels
will remain around 3000 feet through tonight then rise to above 5500
feet Sunday afternoon.

Showers will linger mainly over southwest Washington and along the
coast Sunday night through Monday as the warm front stalls across
Washington State. Most of the precipitation will be along the coast
and the higher terrain, and expect very little rain for the interior
valleys. Rain totals will be 0.50 to 0.75 for the higher terrain of
SW Washington tonight through Monday morning with less than 0.50 inch
for the north Oregon higher terrain, and less than 0.10 inch for the
interior low lands.

A low pressure approaches Monday night with another warm front across
Washington State. This will continue rain north of Salem Monday night
through Tuesday morning. There is more moisture with this front, with
the bulk of the moisture being directed north of the Portland
forecast area. However, the rain will pick up for the south
Washington coast, Willapa Hills, and the south Washington Cascades.
Expect an additional 0.25 to 0.5 inch of rain in these favored
Washington ares Monday night through Tuesday morning.

A cold front will then bring widespread rain to the region late
Tuesday morning or early Tuesday afternoon with gusty south winds.
Expect 0.75 to 1.5 inch of rain with this front Tuesday through
Tuesday night, and 4 to 8 inches of snow  above 4500 feet. ~TJ

.LONG TERM...Tuesday night through Saturday...We will see our first
widespread rain in a while with this system starting Tuesday morning
and continuing through Wednesday morning, with rainfall amounts
around an inch for most of the area. Snow levels will be falling
through this event, falling to around 1500-2000 ft by Wednesday
morning. Showers will be tapering off midday Wednesday. Good news
for skiers is that with ~1 inch of liquid equivalent, and snow
levels starting around 5500 ft, the resorts could see a foot of snow
with this system Tuesday into Wednesday.

Little change in the GEFS ensembles between yesterday and today in
the extended with regards to the uncertainty in the positioning of
the ridge axis. In any case, dry weather looks to return through the
weekend, with east winds funneling cooler air into the Willamette
Valley. Expect more of what we saw last week as we go into next
weekend, with the GFS and the ECMWF suggesting a building pressure
gradient across the Cascades Friday night into Saturday suggesting
increasing winds through the Columbia River Gorge and east Portland
Metro. -McCoy

.AVIATION...Flat high pressure will continue to nose over the
PacNW this evening with a warm front bringing rain to the
northern terminals later this evening and early Sunday. Rain
looks to continue along the north coast and north Cascades
through 18/00z. Wide mix of conditions currently across the
north interior will continue through the evening until the warm
frontal rain brings cigs/vsbys back down to IFR, and maybe LIFR
fog/low stratus in the case of KHIO and KEUG. Expect poor
conditions to continue through 18z Sunday, before improving with
time during the afternoon. KHIO appears to be the last to lift
out of LIFR as late as 17/23z.

PDX AND APPROACHES...Currently MVFR cigs are impacting visual
approaches however, an advancing warm front may keep cigs
bouncing down to MVFR at times through 17/05z. Then have higher
confidence cigs will lower to 005-010 around or shortly after
05z as rain pushes over the field overnight tonight through early
Sunday. Expect low cigs will continue through roughly 20z but
still MVFR and impacting visual approaches through 18/00z.


.MARINE...High pressure offshore will back southerly tonight and
increase as a cold front approaches late this evening. Pushed the
start time of the SCA for winds ahead by a few hours based on
latest model data. Also decided to include the northern inner
waters as there will be enough coastal jet in place to focus the
wind gusts above 20 kt. Seas appear to hold just shy of 10 ft and
have not issued a SCA for seas, but do have some concerns they
may square up again as the winds peak.

A stronger front is modeled to arrive on Tue, and looks like it
is highly probable to bring gale force winds. Another front may
arrive Wed. Then weak offshore flow is expected to develop in the
late week time period. The stronger Tue front will likely push
seas into the low to mid teens before they drop off again during
the second half of the week. JBonk/mh


PZ...Small Craft Advisory for winds from 10 PM this evening to 10 AM
     PST Sunday for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 6 PM
     PST this evening.

     Small Craft Advisory for Rough Columbia River Bar from 2 AM to
     5 AM PST Sunday.


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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.