Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 100036
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
435 PM PST Fri Dec  9 2016

.SYNOPSIS...Frontal zone remains nearly stalled close to Salem this
afternoon, with near-freezing temperatures to the north and
temperatures well into the 40s to the south. This continues to set
the stage for some areas of freezing rain around the Portland Metro
area; particularly near the Columbia Gorge and in the West Hills.
However, temperatures are expected to climb above freezing for all
but the Columbia Gorge and Cascades this evening as the air mass
slowly moderates. Precipitation is increasing as the next disturbance
rides E-NE along the front, so significant additional snow and ice
accumulations are expected in the Gorge, with several inches of snow
for the Cascades. Winds are expected to turn west in the Columbia
Gorge Saturday, finally bringing an end to the snow and ice there.
Otherwise, a series of low pressure systems will maintain showery
weather into next week...with temperatures remaining near or below
normal.

&&

.SHORT TERM...Tonight through Monday...Temperatures continue to very
slowly moderate across the Portland and Vancouver metro area, with
both PDX and TTD climbing to 33 deg F over the past 1-2 hours. There
are still some pockets of subfreezing temperatures in the metro area,
where increasing rain is adding to the existing ice accumulations.
The existing freezing rain advisory looks good until it expires 6 PM;
at this point it appears unlikely we will need to extend it as our
slow thaw is expected to continue across the PDX metro area.

Currently, a nearly stationary front extends from around Estacada to
Salem. To the north of the front, cold Gorge outflow continues to
keep temperatures in the lower to mid 30s. However, sites below
freezing are becoming less and less numerous...likely due to slow
moderation and moistening of the air mass. This trend should continue
overnight. To the south of the front, temperatures are well into the
40s in a milder Pacific air mass and S-SW flow. Milder air has made
it up the coast to Tillamook, but even the cooler air to the north
has moderated into the lower 40s along the coast.

Increasing jet energy continues to push into the Pac NW, adding vigor
to the frontal zone and causing a general increase in precip across
the forecast area. Snow levels range from around 3000 feet or lower
north of Mount Hood, to as high as 5000 feet near Willamette Pass.
Precip is expected to remain fairly widespread tonight before
tapering to less numerous showers Sat morning. Have issued a snow
advisory for the Oregon Cascades, and extended the existing Winter
Storm Warning for the Central Gorge, S WA Cascades and Hood River
Valley to accommodate the 4-8 inches of snow expected tonight and
early Sat from this system. The Columbia Gorge west of Cascade Locks
will remain in the unfortunate spot where temperatures are warm
enough aloft to melt snow, but surface temps are below freezing...
leading to an additional 0.25-0.50 inch of ice on top of the 0.50 to
1.00 inch that has already accumulated. Overall this could end up a
very damaging event in the West Gorge that could take a couple days
to recover from. Areas near Troutdale will be precariously close to
getting in on this icing, but given the current 33 deg F reading at
KTTD, it appears the immediate PDX metro may be spared the worst
impacts.

A cold front is finally expected to push through SW WA/NW OR Sat
afternoon, bringing more showers but also switching the winds to
westerly through the Gorge. This should finally scour out the
low-level cold air and bring an end to the low elevation snow and ice
in and near the Gorge. By the time all is said and done, areas east
of Stevenson and Cascade Locks may end up with 10-18 inches of snow
since Thu.

Onshore flow should cause occasional rain and mountain snow showers
to continue into Sunday, with snow levels lowering to around 2000
feet. The next disturbance looks to enhance precip again Sunday and
we may need another snow advisory for the Cascades and potentially
the higher foothills. Another disturbance will likely bring more rain
and foothill/Cascade snow Monday, though the 18z GFS looks
interesting for potential lower elevation snow by developing another
weak surface low off the N OR Coast while another shot of cold air
pours through the Fraser River and into the Columbia Basin. Models
vary on the details here...so it is too early to tell whether or not
there is a legitimate shot for lower elevation precipitation type
issues Monday at this time.  Weagle

.LONG TERM...Monday night through Friday.  There will be a chance of
showers with valley rain and mountain snow to start the period as an
upper level trough of low pressure slips southward into northern
Calif. On tues, a fairly strong ridge of high pressure begins to
move southward from Canada into eastern Washington with an
accompanying cold airmass. This setup will bring offshore flow to
the region for the middle and latter part of the week. NWP models
indicate there will be a fairly dry period during the middle part of
the week. A fairly strong east-west pressure gradient sets up the
latter part of the week brining some strong easterly winds through
the Gorge by weeks end. tw

&&

.AVIATION...A moist onshore flow pattern will bring a mix of
vfr, mvfr and ifr conditions to most taf sites through 00z Sunday.
Most taf sites will likely hover between mvfr and ifr during this
time as winds weaken overnight and plenty of low level moisture
remains. Freezing rain and snow will become increasingly confined
to the Columbia River Gorge during this time as well.

KPDX AND APPROACHES...Temperatures have warmed to just barely
above freezing and should continue to moderate over the next
18-24 hours. Rain overrunning cold air blowing eastward out of the
Columbia River Gorge will bring a mix of vfr, mvfr and ifr
conditions through 00z Sunday. Mvfr conditions this evening may
temporarily give way to vfr conditions towards 06z Saturday, but
think enough low level moisture will linger that it will be short
lived and will likely only promote lifr/ifr conditions to develop
and linger until winds turn southerly towards 12-18z Saturday.
/Neuman


&&


.MARINE...Winds out of the southwest have decreased some this
afternoon, but still seeing gusts to 20 to 25 kt. Will continue
Small Craft Advisory for Winds as winds will start to come back
up this evening. Seas have come up as expected and are now around
12 ft. Adjusted the forecast a little bit such that seas steadily
climb and peak Saturday evening in the 14 to 16 ft range, which
looks like it will coincide with the highest winds. Winds and seas
both subside through Sunday. Then will get a respite, with
somewhat benign conditions into early next week. Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 4 AM PST Saturday for Central
     Columbia River Gorge-Upper Hood River Valley.

     Ice Storm Warning until 4 AM PST Saturday for Western Columbia
     River Gorge.

     Winter Weather Advisory until 6 AM PST Saturday for Cascades in
     Lane County-Northern Oregon Cascades.

     Winter Storm Warning until 4 PM PST this afternoon for Northern
     Oregon Cascades.

     Freezing Rain Advisory until 6 PM PST this evening for Greater
     Portland Metro Area.

WA...Winter Storm Warning until 4 AM PST Saturday for Central
     Columbia River Gorge-South Washington Cascades.

     Ice Storm Warning until 4 AM PST Saturday for Western Columbia
     River Gorge.

     Freezing Rain Advisory until 6 PM PST this evening for Greater
     Vancouver Area.

PZ...Small Craft Advisory for winds until 10 AM PST Saturday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

     Gale Warning from 10 AM Saturday to midnight PST Saturday night
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 nm.

     Small Craft Advisory for hazardous seas until 10 AM PST
     Saturday for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 5 PM
     PST Saturday.

&&

$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.



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