Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 091213
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
413 AM PST Fri Dec 9 2016

.SYNOPSIS...East winds will remain strong enough this morning to keep
areas near and west of the Columbia River Gorge below freezing.
Light showers will continue to add a light glaze across the north
where temperatures remain sub-freezing. Temperatures will gradually
warm above freezing today except for areas in and near the Columbia
River Gorge. Showers will increase this afternoon and bring a
threat for major icing in the Western Gorge through tonight. A series
of low pressure systems will maintain cool and showery weather into
next week.

&&

.SHORT TERM...Today through Monday...The upper trough axis has
pushed well north of the area bringing southwest flow aloft but the
surface winds remain rather light. Exception is in and downstream of
the Gorge where brisk east winds continue. With the surface low
remaining well offshore and cold high pressure east of the Cascades,
do not expect the cold outflow from the Gorge to give up so easily
today. Unfortunately, this will keep reinforcing the sub-freezing
air this morning for a large part of the Metro area and the northern
half of the Willamette valley largely west of I-5. Should see a
gradual rise to the low land temperatures today with temperatures
rising above freezing by late morning, but there is a chance it will
take into early afternoon. Meanwhile, light showers continue to
stream across the region and are bringing measurable freezing rain
to the aforementioned sub-freezing areas this morning. This will
largely fall as snow for the North Oregon/South Washington Cascades,
The Upper Hood River Valley, and the Central Columbia River Gorge
where the cold pool remains deep.

Another short-wave will brush the region this afternoon and bring an
intensification to the showers...particularly along the Cascades,
Foothills, and the Gorge. This will likely bring just enough mixing
to elevate temperatures in most of the cold air trapped locations
west of the Cascades. Unfortunately, the cold east flow through the
Gorge will dominate leaving the Western Gorge susceptible for
significant ice accumulations later this afternoon and tonight. Am
expecting up to 0.75" of new ice to be deposited and have replaced
the Winter Storm Warning with an Ice Storm Warning there. Have also
extended the Winter Storm Warning for the North Oregon Cascades
through this afternoon as the threat for pockets of freezing rain
will continue, especially for the travel corridors. Will need to
consider extending the Winter Storm Warning for the Cascades, but
really want to see how the vertical temperature profiles and
resulting snow levels respond to today`s action first.

Saturday and Sunday, another low pressure area will brush north of
the region Saturday afternoon. It does appear there will be enough
influence to shift the area of relatively higher pressure from east
of the Cascades to Southwest Oregon. This should be enough to pinch
off the east winds and allow a light westerly flow to develop
through the Gorge by early Saturday morning. It`s still a little
iffy to say it will be strong enough to end the freezing rain threat
right away. Have modest confidence, however, as have seen widespread
acceptance among the mesoscale models and their higher resolution
variants. Snow levels will lower to around 3000 feet but QPF amounts
imply there will only be a handful of inches of new snow
accumulations over the course of the day. Lower elevations will
continue to see a rather cold rain. /JBonk

.LONG TERM...Sunday night through Thursday...No changes. Previous
discussion follows...Onshore flow for the start of next week when
maintain shower chances across the region early next week. The
overall weather pattern remains rather progressive, with several
impulses passing across the region and providing for increased
precipitation chances. Snow levels remain around 2,500 feet through
the start of next week, so expect continued snow to pile up in the
Cascades, and a chance for some additional snowfall down in the
higher Cascade foothills and the highest parts of the Coast Range.
Forecast models are in good agreement in bringing a plume of enhanced
moisture to the West Coast around midweek, but still some significant
uncertainty in the strength and timing of the upper trough. This may
result in a dry time of a day or so later in the week, but given
significantly different solutions, will continue to utilize a blend
of model solutions and the previous forecast to generalize decreasing
PoPs across the north but higher across the southern portion of the
CWA for midweek with the idea that the core of moisture will stay in
southern Oregon and northern California. There is some potential for
a much colder air mass in place by the end of the week that could
bring lowering snow levels, but will wait for more continuity in the
overall pattern before moving too far this direction. Cullen
&&

.AVIATION...Rotten day for flying, unless training for IFR flight.
Considerable MVFR stratus over interior this am, with areas of IFR
here and there. Widespread mtn obscurations through this evening.
Best conditions on the coast, with VFR and pockets of MVFR cigs.
Not much change today in the overall pattern, as onshore flow will
maintain scattered showers. Cold air will still seep westward into
the lowlands via the Columbia River Gorge. Expect mix of sleet
and/or freezing rain in the interior lowlands between Wilsonville
and Kalama through about 20Z, and in the Columbia Gorge all day.

KPDX AND APPROACHES...Generally MVFR cigs will persist today,
though will see occasional brief IFR stratus this am. Main problem
is continued cold outflow from Gorge. This keeping temperatures at
or just below freezing this am, so expect continued occasional
freezing rain. East winds will continue to weaken late today into
tonight, and will probably turn more southeast at that time.
Either way, still think temperatures will moderate enough to end
freezing rain threat between 18z and 21Z.              rockey.

&&

.MARINE...Overall, not a lot of change. Breezy south to southwest
winds of 15 to 25 kt will continue today through tonight. Have
decided to push back onset of Gales until later Sat am, as am
waiting for the surface low to push across the northeast Pacific
and into southern British Columbia on Sat. Gradients not all that
impressive until later Sat am, so that is main reason for the
delay.

Seas running 7 to 10 ft this am, but will gradually build through
tonight and Sat. Likely to build back into the lower teens range
this afternoon, and hold in the 13 to 15 ft range tonight. As
winds pick up on Sat, will see the seas build further, running 17
to 20 ft by afternoon. Highest seas will be over Washington
waters, with strongest winds. Winds as seas both subside rather
quickly Sat night, as front will push onshore early Sat evening.
Then will get a respite, with somewhat benign conditions for
Sunday into early next week.                           Rockey.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Ice Storm Warning until 4 am Saturday for...
        Western Columbia River Gorge.

     Winter Storm Warning until 4 PM today for...
       Central Columbia River Gorge
       Upper Hood River Valley
       North Oregon Cascades.

     Freezing Rain Advisory until 10 am today for...
        North Willamette Valley, including Greater Portland Metro
        Central Willamette Valley, including Salem Area
        Lower Columbia
        Coast Range of Northwest Oregon
        Foothills of the North Oregon Cascades.

WA...Ice Storm Warning until 4 am Saturday for...
        Western Columbia River Gorge.

     Winter Storm Warning until 4 PM today for...
        Central Columbia River Gorge
        South Washington Cascades.

     Freezing Rain Advisory until 10 AM today for...
        Clark County, including Greater Vancouver Area
        I-5 Corridor in Cowlitz County
        South Washington Cascade Foothills
        Willapa Hills.

PZ...Small Craft Advisory for winds and seas today through 10 am
        Saturday on all coastal waters.

     Gale Warning from 10 AM Saturday through Sat evening on all
        coastal waters.

     Small Craft Advisory for Rough Columbia River Bar from 10 AM
        this morning to noon 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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