Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 100458
AFDPQR

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

.SYNOPSIS...Frontal zone remains nearly stalled north of Salem this
evening, 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 later tonight 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...offshore flow continued
through the gorge this evening, but in recent hours had shown a
modest weakening of the gradient. The frontal boundary separating
the warm air, with temps in the 40s, in the south half of the valley
from the cold air in the north, where temps were in the lower to mid
30s, remained between SLE and UAO. Temps in the Portland metro area
and in the gorge have been fairly steady through the afternoon and
evening, in the 20s in the gorge and in the lower 30s in the metro
area. Models indicate some weakening on the offshore gradients later
tonight as a shortwave moves across late in the night, with the flow
eventually turning weakly onshore by morning. The weakening gorge
gradient should ultimately allow slow moderation of temps overnight,
but unsure of how long this will take given the persistence of the
cold air today. Ice storm in the west Gorge will continue tonight as
temps remain in the 20s and freezinf rain continues. With temps
still hovering right around freezing in parts of the metro area,
most notably near the mouth of the gorge and in the upper West
Hills, will keep the advisory for freezing rain going into late
tonight. However, the advisory is mainly for a rather limited area,
with the rest of metro area unlikely to see much additional ice
accumulations outside of those just mentioned. In the central gorge
models hint at enough warming aloft for some threat of freezing rain
out as far as Hood River later tonight. Have seen no indication of
that yet, but ODOT observations between Hood River and Cascade Locks
have indicated freezing rain in at least parts of the central Gorge,
so will add that into the mix for tonight. Elsewhere the forecast
looks on track tonight as the shortwave will keep pops high through
most of the night.

Remainder of short term discussion unchanged...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...Moist mild air flowing over the top of cold air
spilling out of the Columbia River Gorge will bring a mix of ifr
and mvfr conditions to PDX metro taf sites tonight before
improving Saturday. A milder southerly wind pattern along the
coast and in the central and southern Willamette Valley should
generally produce a mix of mvfr and vfr conditions through 06z
Sunday.

KPDX AND APPROACHES...Temperatures continue to hang just barely
above freezing at the terminal. Expect this trend to continue
overnight before temperatures moderate Saturday. There is a 30%
chance that temperatures could briefly dip back below freezing
during a heavier shower, but thinking any freezing rain would very
short lived and is not worth mentioning in the forecast at this
point. There may also be some tendency for skies to become a
little more broken towards 12z Saturday, which in combination with
decreasing winds could quickly freeze any water on runways.
Suspect this won`t happen, but there is certainly a chance for it
to occur. As for flight conditions, expect a mix of mvfr and ifr
conditions through ~15-18z Saturday before increasing southerly
winds likely produce improving flight conditions. /Neuman

&&

.MARINE...A front will bring increasing southwesterly winds with
widespread gusts of 25 to 30 kt Saturday and Saturday night to
the waters. Latest model guidance has backed off on the idea that
winds will peak in the 35 kt range during this time, but opted to
continue the Gale Warning for Saturday PM. It may need to be
canceled early. Nonetheless, a westerly swell between 13 and 15 ft
will push into the waters Saturday PM.

A couple weak surface low pressures moving eastward towards the
Strait of Juan de Fuca Saturday night and Sunday will keep small
craft advisory level wind gusts of 25 to 30 kt across the waters
through Sunday. However, pressure gradients really disintegrate
Sunday night and Monday, which should bring an end to any wind
concerns, which will help seas decrease as well.

There may some issues with offshore winds at times next week, but
all in all, sea conditions look to be relatively quiet given the
time of year. /Neuman

&&

.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.

     Freezing Rain Advisory until 4 AM PST Saturday 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 4 AM PST Saturday 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
     midnight PST Saturday night.

&&

$$

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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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