Strong Wind in Oregon, February 1 to 2, 2017

Area Forecast Discussion
National Weather Service Portland OR
251 AM PST Wed Feb  1 2017

.SYNOPSIS...A well developed low remains parked to our
southwest off the southern Oregon and northern California coast
today. East winds will strengthen today and snow levels will lower
to near the valley floor. A weak front will slowly drift north today
for occasional light rain and snow with little to no accumulations.
A stronger front is forecast to lift north from the low Thursday
afternoon through Friday for snow, sleet, and freezing rain for the
interior low lands and snow for the Cascades.  The precipitation will
turn to mostly freezing rain through the day Friday except snow will
continue in the Gorge and Cascades. The precipitation west of the
Gorge will turn to rain from south to north late Friday and Friday
night. Active weather continues through early next week, with more
low elevation snow possible.
&&

.SHORT TERM...Today through Saturday...Satellite imagery shows a
surface low around 35N 140W early this morning which is around 900
miles offshore of Eureka, California. The baroclinic zone that
stalled over Lane County last night still remains there this morning,
but is much weaker and is not producing much precipitation. High
clouds over Lane County has limited with this weakening boundary has
limited cooling and temperatures across Lane County remain above
freezing. Clearing north of this boundary combined with cooler air
moving in from the north is resulting in cooling this morning for
areas north of Lane County with temperatures in the low to mid 30s.

Temperatures in south Washington and north Oregon east of the
Cascades are dropping rapidly this morning as a cold high pressure
begins to moves into those areas from the north. This will encourage
the east surface pressure gradient to increase today. Currently the
Dalles to Troutdale east gradient is around 5 mb.  This gradient is
expected to increase to around 8 mb by noon today and remain around 8
to 10 mb through late Thursday night. This will result in breezy east
winds across the area with gusts 60 to 80 mph through the Western
Columbia River Gorge, and gusts to around 55 mph for the East
Portland Metro Area that are normally impacted by the gorge entrance.
These gusts are covered in the wind advisory that is in effect from
early this morning to early Friday morning.

The east winds will pull the cold temperatures from east of the
Cascades to the Willamette Valley with widespread temperatures
cooling below freezing tonight. Areas impacted by the east winds
(mainly north of Salem) may not warm above freezing Thursday.

A warm front associated with the offshore low draped across northern
California early this morning will move north today and merge with
the remnants of the baroclinic zone later this morning. This will
result in occasional light rain or snow today and this evening for
areas mainly south of the Portland metro area. The moisture is not
impressive and do not think there will be any accumulations or
impacts to the low lands, but the Cascades and higher Cascade
foothills may get a light dusting. This front falls apart over the
region tonight with most areas dry yet cold as the east winds
continue.

A slightly moister warm front will then move south to north Thursday
followed by a moist cold front on Friday. The models vary on the
available moisture, but agree that the precipitation type will likely
start out as snow early Thursday before switching to sleet or
freezing rain south of Salem Thursday afternoon and north of Salem
Thursday night and Friday. Models forecast the east winds will
decrease Friday night and south winds will warm areas outside of the
gorge above freezing ending the threat for wintery precipitation.
However we all know by now that the models tend to weaken east winds
too early and that the timing of the end of winter precipitation for
the east Portland area may need to be extended in time.

The gorge and the Upper Hood River valley can expect snow to begin
Thursday afternoon and turn to a mix of sleet snow and freezing rain
near the Gorge entrance Friday afternoon, near Cascade Locks Friday
night, and the Upper Hood River Valley early Saturday morning.
Currently expect the precipitation to turn to all rain for the Upper
Hood River Valley Saturday night. The north coast may see occasional
snow or sleet, but do not expect much if any accumulations.

The pressure pattern with this weather event is similar to the Jan 10
event when we received more snow and ice than expected. There is an
obvious difference between these events though, the air mass
preceding the January storm was much colder than the current air
mass. However, things to watch with this upcoming system that may
result in more qpf is rapid frontogenesis and thunderstorms.  Right
now neither of these seem very likely and will remain with the
current snow and ice amount forecast. Confidence in precipitation
amounts is low, but there is potential for the interior low lands
(excluding the Gorge and Hood River Valley) to see 1 to 2 inches of
snow and/or 0.10 to 0.25 inch of ice Thursday afternoon through
Friday night.  The Gorge and Upper Hood River Valley could see 4 to 8
inches of snow and around a half of an inch of ice. The winter
weather watch remains unchanged. ~TJ

.LONG TERM...Saturday night through Tuesday night...from previous
discussion...Rain continues for most of the region into the weekend
in a fairly active pattern, with periods of heavy precipitation as
reinforcing disturbances rotate around the broad upper low that
remains firmly in place off the northern end of Vancouver Island
through the weekend. Meanwhile, snow will continue in the Cascades,
with snow levels climbing slightly but remaining below about 5,000
feet through the entire weekend.

Details in the models become a bit less consistent by the end of the
weekend into early next week as the next week, partially due to the
influence of a more progressive upper low undercutting the northern
stream low that remains in more of a blocking position downstream of
the strong ridge over Alaska. While the latest ECMWF suggests more
interaction and a well-defined surface low moving up the coast,
these two systems remain somewhat out of phase in the latest
deterministic GFS run, with the bulk of the energy and significant
moisture heading south into California. Thus, due to the significant
spread among forecast models, have for now maintained a more
conservative approach to the forecast for the start of next week,
with snow levels lowering only to around 1,500 feet on Monday as
enhanced moisture moves into the region. However, given both the low
confidence in the overall evolution of the pattern and some support
among several of the GEFS ensemble members, can not rule out the
possibility of low-elevation snow again around Monday of next week.
However, by midweek, expect a trend for increasingly dry and warmer
conditions as the persistent upper low finally moves out of the
region and heights begin to rise.   Cullen
&&

.AVIATION...High pres over eastern Washington will maintain
moderate to strong offshore flow for today through Thu. Weak
warm front near Calif/Ore border will slowly drift northward
later today and tonight. This will push increasing mid-level
clouds, 6000 to 9000 ft, northward today and tonight. Most of
the area will remain dry, but expect occasional flurries or even
spotty light snow tonight, especially over the Cascades.

KPDX AND APPROACHES...VFR with increasing mid and high clouds
later today. East winds will ramp up today, with gusts 35 to 45
kt to east of KPDX this afternoon and tonight, with gusts lower
to west of the field. Could see occasional flurries later today
into this evening, but little if any accumulation.   /Rockey.
&&

.MARINE...Winds today through Thu night will be influenced
strongly by the strong high pres over the inland Pac NW. This
will maintain gusty easterly winds through Thu night, with the
strongest winds being tonight and Thu with gusts 25 to 35 kt for
most areas, but gusts 30 to 40 kt on the outer waters, beyond 10
nm, on the Washington waters south to off Cascade Head. With
these gusty winds, expect steep and choppy wind-driven seas of 7
to 10 ft, but 10 to 12 ft in north offshore waters.

Low pres well off the north Calif coast over the next few days
will push northeast and into Vancouver Island later Fri. As it
moves, winds will ease and becoming southerly later Fri into Fri
night. Unsettled over the weekend, but winds look to stay down
under 20 kt Sat into Sun. Another low pres moves across the
coastal waters late Sun, with another round of gusty southerly
winds. Seas will continue to run 8 to 11 ft this weekend.

Plenty of model uncertainty for early next week, but now appears
weather remains unsettled, with another low that will track off
the NE Pac and into south Oregon/far north Calif late Mon.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Watch for Thu evening through Sat for...
	Western Columbia River Gorge
	Central Columbia River Gorge
	Hood River Valley.

    Winter Storm Watch Thu afternoon through Fri evening for
	Coast Range of Northwest Oregon
	Northern Oregon Cascade Foothills
	Central Willamette Valley, including Salem area.

    Winter Storm Watch Thu am through Fri afternoon for
	South Willamette Valley, including Eugene/Springfield
	Cascade Foothills in Lane County
	Central Coast Range of Western Oregon.

    Wind Advisory until today through late Thu night for...
	North Willamette Valley, including Greater Portland Metro.

    Winter Storm Watch Thursday evening through Fri night for
	North Willamette Valley, including Greater Portland Metro
	Lower Columbia.

WA...Winter Storm Watch from Thu evening through Sat for...
	 Central Columbia River Gorge
	 Western Columbia River Gorge.

     Wind Advisory today through Thu night for...
	 Clark County including Greater Vancouver Area.

     Winter Storm Watch Thu evening through Fri night for...
	 Clark County including Greater Vancouver Area
	 I-5 Corridor in Cowlitz County
	 South Washington Cascade Foothills
	 Willapa Hills.

PZ...Gale Warning today through Thu afternoon on the coastal
     waters from Cape Shoalwater to Cascade Head.

     Small Craft Advisory for winds today through Thu on the
     coastal waters from Cascade Head to Florence.
&&

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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.