Cold in Oregon, January 1 to 11, 2017

Area Forecast Discussion
National Weather Service Portland Oregon
245 PM PST SUN JAN 1 2017

.SYNOPSIS...Low pres over sw WA early Sun afternoon will move
sw off the Oregon coast tonight. Cold high pres from the Canadian
Prairies will move south and settle in over the northern Rockies for
the first half of the week, setting up a cold offshore flow over the
Pacific NW. A chance for snow showers will remain, mainly over the
Cascades and the far southern parts of the forecast area for the
next few days. The forecast for the latter half of the week and into
the weekend becomes rather muddled, but at some point moisture
lifting up over the cold air will bring a chance for some low
elevation snow.
&&

.SHORT TERM...Tonight through Wednesday...A low center was seen in
satellite imagery this afternoon over sw WA entering Clark County,
slowly moving south. Showers seen on radar through early afternoon
have tended to become a little more orographic in nature, favoring
the Cascades and OR Coast Range. One other significant area of
persistent snow showers was over interior sw WA in the deformation
zone to the north of the low, but the deformation zone appeared to
be finally breaking up by mid afternoon. Models continue a trend of
very slowly shifting the upper low sw off the coast tonight and
Monday, while the surface low is a little quicker to move offshore
tonight. The transition to offshore flow will allow colder drier air
to filter into the region from the north and east tonight and
Monday. Snow showers will continue to diminish, but it may be
difficult to completely shut off the snow showers as the upper
trough lingers over the region as well as some mid level moisture.
Will carry small pops through the day Monday over all but the nw
part of the forecast area, then limit the chance more to the
Cascades and far south Mon night and Tue as low level cold dry air
continues to push in.

With the cold high setting up east of the Cascades Mon night through
Wed, the offshore flow will bring strong winds to the west end of
the Gorge and into the eastern part of the Portland metro area.
Model surface pres gradients on the order of 12 to 15 mb suggest
winds gusting as high as 60 mph in the west Gorge, except of course
for the normally higher localized gusts at Crown Point. Model 850 mb
temps by Tue morning generally on the order of -10 deg C, promising
some of the coldest temps in the past few years. Clouds and winds in
some areas will determine how cold it will get overall, but at least
some outlying areas in the interior valleys appear likely to see
lows drop into the teens while highs in interior valleys will
struggle to approach freezing Mon through Wed, and even at the coast
highs are likely to be stuck into the 30s.

.LONG TERM...Wednesday night through Sunday...Anyone have a coin
to flip?  GFS and EC offer two very different solutions to the
extended period, and looking at ensemble information does not offer
much clarification. GFS indicates ridging over the Pacific NW during
the latter of half of the week in response to deepening low well
offshore, leading to warming temps and moisture spreading up over
the area, with the implication of low elevation snow. EC maintains a
dry offshore flow over most of the area with a little moisture
spilling up into the southern part of the forecast area, as a
westward extension of the cold trough over the northern rockies and
plains. CMC solution lends support to the EC solution, but given
past model run difficulties in settling on a consistent solution,
will need to go with more of a blend of solutions mildly favoring
the colder and drier EC. Over the weekend models come back into
better agreement as another low digs s off the BC coast, eventaully
spreading moisture back into the region. If cold air is maintained
ahead of this system as in the EC, the end result would be a low
elevation snow and ice event, while the warmer GFS suggest rain.
Again, given the issues the models have leading into the weekend,
confidence in any specific outcome will be quite low. &&

.AVIATION...Surface low remains to slowly meander. Some organized
areas of showers continue to rotate around the low, with the
strongest of these producing snow in the vicinity of the upper
low. A small band of steady moderate snowfall has impacted KKLS
and will continue moving slowly along I-5 in SW Washington. For
the terminals, expect some mixed wet flakes with rain at most,
but generally no snow accumulation. Generally VFR conditions
across the area through the evening, but brief MVFR conditions
possible in the heavier showers through evening. As the low moves
south across the region and eventually weakens, expect drying and
clearing to begin by late this evening across the northern half of
the area, but some lower VFR to MVFR cigs will persist longer
overnight with showers south of a roughly Mt. Jefferson to KONP
line.

KPDX AND APPROACHES...VFR conditions continue with occasional
showers due to nearby surface low through the evening. These
showers may bring some brief reductions to MVFR through the
evening, but moisture should taper off by late evening with
conditions becoming primarily VFR overnight. Surface wind becomes
east around 08z and persists through remainder of the TAF period.
Cullen

&&

.MARINE...Seas will peak in the 17 to 20 foot range, with the
largest seas over the outer waters and generally south of Cascade
Head. Closer to the coastline, expect seas in the 14 to 18 ft
range during this same time.

Offshore flow pattern develops late Sun night and continues
through at least mid-week. Models suggest a fairly strong and deep
offshore flow pattern, with small craft advisory wind speeds
likely over much of the waters by Mon night or Tue. Model
differences increase during the latter half of the week, so low
confidence in specifics of the forecast beyond Wednesday night.

Once the offshore flow pattern commences, seas will drop off
fairly quickly, falling below 10 ft by 18Z Mon, then to around 5
ft by mid-week. Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 3 PM PST this afternoon for
     Central Columbia River Gorge-Greater Portland Metro Area-
     Western Columbia River Gorge.

     Winter Weather Advisory until midnight PST tonight for Cascade
     Foothills in Lane County-Central Coast Range of Western
     Oregon-Central Willamette Valley-Northern Oregon Cascade
     Foothills-South Willamette Valley.

WA...Winter Weather Advisory until 3 PM PST this afternoon for
     Central Columbia River Gorge-Greater Vancouver Area-
     Western Columbia River Gorge.

PZ...Small Craft Advisory until 10 PM PST this evening for Waters
     from Cape Shoalwater WA to Cascade Head OR from 10 to 60
     nm.

     Small Craft Advisory for winds until 7 PM PST this evening for
     Waters from Cascade Head to Florence OR from 10 to 60 nm.

     Small Craft Advisory for hazardous seas until 4 PM PST Monday
     for Coastal waters from Cape Shoalwater WA to Cascade Head
     OR out 10 nm-Coastal Waters from Cascade Head OR to
     Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 4 AM
     PST Monday.

&&

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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.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PORTLAND OR
545 PM PST SUN JAN 01 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0540 PM     SNOW             CANBY                   45.27N 122.69W
01/01/2017  E0.5 INCH        CLACKAMAS          OR   TRAINED SPOTTER

            TRAINED SPOTTER REPORTS 0.5 INCH OF SNOW HAS ACCUMULATED
            IN LAST 15-20 MINUTES...STILL SNOWING HARD.

&&

SWEAGLE