Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 091928
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
1128 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 and possibly the West Hills. Showers will increase this
afternoon and evening...bringing a threat for major icing in the
Western Gorge through tonight. A series of low pressure systems will
maintain showery weather into next week...with temperatures remaining
near or below normal.

&&

.SHORT TERM...Today through Monday...Temperatures are very slowly
moderating across much of the district this morning; however areas in
the West Hills of Portland, much of Clark County, and near the
Columbia Gorge remain very icy as temps persist in the 30-32 deg F
range. Decided to extend the Freezing Rain Advisory until 6 PM, but
added detail to the advisory which highlighted these areas for an
additional 0.10-0.20" of ice before temps finally rise decidedly
above freezing this evening. It appears temps are generally 32-34 deg
F in Downtown Portland and Vancouver, as well as much of the West
Metro. Therefore conditions should be improving/thawing in these
areas, especially with some help from solar heating despite the cloud
cover. Allowed the FZRA advisory to expire elsewhere, and kept the
West Gorge Ice Storm Warning and other Winter Storm Warnings as
is...though the Cascades and perhaps Upper Hood River Valley will
likely need advisories or warnings for heavy snow tonight into
Saturday. Decided to punt on this until the afternoon package in
order to focus on the ongoing situation. Previous discussion from 413
AM follows, and much of the reasoning laid out in the discussion
remains valid.Weagle

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...IFR cigs have developed this morning just ahead of a
warm front, the same front which has been creeping its way north
through Oregon for the last 24+ hours. Expect mostly persistence
through the day today. Best conditions are on the coast, with
MVFR cigs and occasional pockets of VFR. 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 and directly adjacent to the Columbia Gorge all
day.

KPDX AND APPROACHES...Generally MVFR cigs will persist today.
Main problem is continued cold outflow from the gorge keeping
temperatures right at freezing. Until winds turn to out of the
south, will continue to see freezing temps and -FZRA when
precipitation is falling. Winds are starting to moderate slightly
with direction trending a little bit more toward SE, but think
temperatures will not rise above freezing until at least 22Z. In
fact, don`t expect winds to switch fully south until closer to
03Z, but think there`s a chance some heating from the sun (despite
the clouds) could occur in the afternoon. May see IFR cigs reach
the terminal after winds go south. Bowen

&&

.MARINE...Overall, not a lot of change. Breezy south to southwest
winds of 15 to 25 kt will continue today through tonight. Seas
running 8 to 11 ft this am and will very gradually build through
the day. As winds pick up on Sat, will see the seas build even
further, running 15 to 18 ft by afternoon. Highest seas will be
over Washington waters, with strongest winds. Winds and 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. Bowen/Rockey

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 4 PM PST this afternoon for Central
     Columbia River Gorge-Northern Oregon Cascades-Upper Hood
     River Valley.

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

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

WA...Winter Storm Warning until 4 PM PST this afternoon 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 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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