High Wind in Oregon, January 10, 2020

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
925 AM PST Fri Jan 10 2020

Updated Aviation Section

.SYNOPSIS...Very active weather pattern will resume Friday with
periods of valley rain, heavy mountain snow and occasionally windy
conditions through the weekend. Colder air will move into the region
early next week, bringing an increasing potential for snow down to
the lowest levels. Details and timing remain uncertain, and
refinements to the forecast are likely over the coming days.

&&

.SHORT TERM...Today through Sunday...Start of an active weather
pattern begins today.  A 979 MB low center offshore of Haida Gwaii
continue to track southeast overnight. Extending south of the low is
a warm front currently approaching the coast as picked up by NWS
network radar.	The cold front is about 500 miles off the WA coast.
This warm front will spread rain mainly for the north half of the
forecast area along with windy conditions at the coast.  The cold
front will push through this afternoon bringing valley rain and lots
of mountain snow through the weekend. Snow levels around 1500-2500 ft
early today will rise to around 3500 ft then drop to around 2500 ft
Sat.  Strong orographic flow behind the front with 850 mb winds 35 to
45 kt will enhance snowfall rates resulting expected 1 to 3 feet
snowfall through Sat morning.  Snowfall rates should ease Sat
afternoon and evening, but the next system arrives Sat night and Sun.
 With similar orographics as the first system, could see about
another foot or two of snow with this system on Sunday and may need
to extend the warning.	For now the Winter Storm Warning continues
for our Cascades zones through Sat morning. Expect travel conditions
will be treacherous across the Cascades for much of the period
between Friday and Sunday, if not longer.

Wind associated with this system should bring wind gusts just under
high wind criteria at the coast and coastal mountains today.  The
strongest winds will be the southerly winds this morning, but gusty
westerly winds will continue tonight behind the cold front.  Perhaps
a little more unusual is wind in interior lowlands.  There is decent
potential for south to southwest wind gust 35 to 45 mph for the
Willamette Valley, Clark County, I-5 Corridor in SW WA zones this
afternoon through most of tonight.  Models show the time window for
strongest winds is from late this afternoon and evening as the wind
speeds and surface pressure gradient are most favorable.  By late
evening the lower level winds turn more westerly reducing the wind
momentum mixing down to the surface.

Rainfall for the lower elevations will be significant as well Friday
through Sunday. Up to 4 inches of rain total are possible for the
coast, Willapa Hills, and the northern and central Coast Range of
Oregon, with up to 2 inches possible for the inland valleys. While
significant, this is unlikely to be enough to cause hydrologic issues
other than minor urban flooding in areas of poor drainage.

Hazards at the coast - This system will be coming at the time of some
of the highest tides of the year. The high tides and strong winds
associated with this system is expected to create minor tidal
overflow and hazardous surf conditions through the weekend. The times
of highest tides will be around noon each day Friday, Saturday, and
Sunday. The greatest impacts will likely be within a couple of hours
before or after these high tides.
/mh/Weagle/Weishaar

.LONG TERM...Sunday night through Thursday...The general theme
for the extended period can be characterized as cold and unsettled.
Cool northwest flow aloft will continue over the forecast area Sun
night into Mon. The operational GFS and ECMWF show the arctic
frontal boundary in northern Washington 12Z Mon and latest ECMWF and
GFS are similar.  However, forecast 850 mb temps valid 12Z Mon are -6
to -8C across SW Washington and NW Oregon. This is borderline for
snow down to the valley floors, especially with onshore low-level
flow.

Forecast details become more fuzzy Mon and beyond though Thu 12Z and
latest ECMWF and GFS are coming to closer agreement regarding surface
low development Mon through Mon night. The operational GFS has been
stronger with the low and tracking it somewhere south of the WA/OR
border Mon night.  ECMWF has been weaker and much further south,
toward southwest Oregon.  The last couple of runs take the low
further north. GEFS ensemble mean takes the low across the central
Willamette Valley Mon night but is slower than the ECMWF. As
discussed earlier, the path and strength of the low will have a
significant impact on lowland snow potential. Forecast 850 mb temps
fall to around -14C at KDLS to -8C at KPDX 12Z Tue.  This would
definitely be cold enough for snow to the valley floor north of
about KSLE, especially with low-level offshore flow developing
through the Gorge as the low tracks south of the WA/OR border.	With
models coming into closer agreement confidence is increasing for
lowland snow in the Mon night to Tue time frame.

Previous discussion follows...There appears to be a precipitation
lull Tue afternoon through Wed morning, but plenty of uncertainly
regarding the location of the arctic boundary. The ECMWF continues to
keep this boundary more north than the GFS. Models typically do not
handle the arctic boundary all that well. The Wed through Thu time
frame will be of most concern. The operational ECMWF and GFS show a
deepening surface low near 130W 18Z Wed. The ECMWF drives this low
inland Wed night, with the main surface low entering SW Oregon 06Z
Thu and then swinging north overnight. The GFS keeps the surface low
offshore through Thu and swings it north off the south Washington and
north Oregon coast Thu afternoon. Should the ECWMF verify, there is
the potential for a significant over-running frozen/freezing precip
event for the north half of the forecast area. As an example, the 12Z
ECMWF snowfall accumulation for KPDX shows several members with 10+
inches total between Wed morning through Thu. However, there is
considerable variance among the individual ECMWF members Wed night
through Thu, with several showing no obvious surface low circulation
off the coast. To make matters even more confusing, the NBM indicates
a 50th percentile 24-hr snowfall 12Z Wed through 12Z Thu for KPDX
around 10 inches. The 90th percentile value is an astonishing 15
inches, with at least a foot extending southward to KEUG. Of course,
considerable uncertainty exists beyond Mon and forecast details will
change over the next few days. Weishaar

&&

.AVIATION...Flight conditions have generally been on a downward
trend this morning with the approach of a frontal system. Coastal
areas will be IFR to MVFR through 12Z Sat. Inland areas are
mainly VFR as of 17Z, but will become primarily MVFR by 20Z.
There is a chance inland areas will see more low-end VFR late
this afternoon just ahead of the cold front.

South wind 20-30 kt with gusts up to 45 kt along the coast
through the afternoon, followed by a shift to SW to W around 00Z
Sat. There will be another burst of wind in the 03Z-09Z Sat time
frame. Wind gusts 25-35 kt likely at the inland TAF sites late
this afternoon through at least 08Z Sat.

KPDX AND APPROACHES...Low-end VFR at the terminal as of 17Z, but
conditions to lower into MVFR by late morning. Conditions to
remain MVFR this afternoon through Sat morning. South wind will
increase this afternoon, with gusts to 30 kt. There looks to be a
minor lull in the wind late this afternoon, but gusty post-
frontal SW wind develops this evening, with gusts to 35 kt
likely through at least 15Z Sat. Light east wind near KTTD will
become S-SW by early afternoon. Weishaar

&&

.MARINE...South winds are beginning to increase early this
morning with the crossing of a warm front, and buoy 46089 is
reporting Gales. Gale conditions will spread NW to SE throughout
this morning reaching the waters offshore of Newport Oregon mid
morning. The winds will decrease this afternoon, with speeds
falling below Gale criteria briefly late this afternoon. However,
gales return a few hours later with the following cold front, and
have extended the Gale Warning out to Saturday afternoon which
includes the south gales ahead of the cold front, and NW gales
behind the front.

The seas build with the Gales today to around 16 feet this
afternoon. These seas will be steep with wave periods around 9
seconds. A very high tide this afternoon could result in tidal
overflow flooding near the beaches with the high tide around 11
AM this morning. A longer period west swell combined with steep
wind waves will result in the seas building to 20 feet by
midnight tonight, and possibly up to 30 feet early Saturday
morning. These larger seas will result in hazardous surf along
the beaches and high rises of sea water on to the beaches. Gales
will ease Saturday evening, and seas will fall below 20 feet
late Saturday night.

Another frontal system will produce another round of gales on
Sunday with seas likely building above 20 feet again Sunday
evening. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until noon PST Saturday for Northern
     Oregon Cascades.

     Winter Storm Warning until noon PST Saturday for Cascades in
     Lane County.

     Wind Advisory from 1 PM this afternoon to 4 AM PST Saturday for
     Central Willamette Valley-Greater Portland Metro Area-
     Lower Columbia-South Willamette Valley.

     Coastal Flood Advisory until 2 PM PST this afternoon for
     Central Oregon Coast-North Oregon Coast.

WA...Winter Storm Warning until noon PST Saturday for South
     Washington Cascades.

     Wind Advisory from 1 PM this afternoon to 4 AM PST Saturday for
     Greater Vancouver Area-I-5 Corridor in Cowlitz County.

     Coastal Flood Advisory until 2 PM PST this afternoon for South
     Washington Coast.

PZ...Gale Warning until 4 PM PST Saturday for coastal waters from
     Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory from noon today to 4 PM PST Saturday for
     Columbia River Bar.

&&

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This discussion is for Northwest oregon and Southwest Washington
from the Cascade crest to 60 nm offshore. This area is commonly
referred to as the forecast area.

Special Weather Statement...CORRECTED
National Weather Service Portland OR
404 AM PST Fri Jan 10 2020

ORZ001>008-010-012-014>016-WAZ020>022-039-040-045-046-110000-
North Oregon Coast-Central Oregon Coast-
Coast Range of Northwest Oregon-
Central Coast Range of Western Oregon-Lower Columbia-
Greater Portland Metro Area-Central Willamette Valley-
South Willamette Valley-Northern Oregon Cascade Foothills-
Cascade Foothills in Lane County-Upper Hood River Valley-
Western Columbia River Gorge-Central Columbia River Gorge-
Willapa Hills-South Washington Coast-I-
5 Corridor in Cowlitz County-Greater Vancouver Area-
South Washington Cascade Foothills-
Including the cities of Astoria, Cannon Beach, Tillamook,
Netarts, Pacific City, Lincoln City, Newport, Cape Foulweather,
Yachats, Florence, Vernonia, Jewell, Sunset Summit, Lees Camp,
Trask, Grande Ronde, Burnt Woods, Tidewater, Swisshome, Veneta,
St. Helens, Clatskanie, Hillsboro, Portland, Wilsonville,
Oregon City, Gresham, Troutdale, Salem, McMinnville, Woodburn,
Stayton, Dallas, Eugene, Springfield, Corvallis, Albany, Lebanon,
Sandy, Estacada, Silver Falls State Park, Sweet Home, Vida,
Jasper, Lowell, Cottage Grove, Parkdale, Odell, Corbett,
Rooster Rock, Multnomah Falls, Cascade Locks, Hood River,
Willapa, Frances, Elk Mountain, Ryderwood, Raymond, Long Beach,
Ocean Park, Naselle, Cathlamet, Cape Disappointment, Longview,
Kelso, Castle Rock, Vancouver, Battle Ground, Ridgefield,
Washougal, Yacolt, Amboy, Toutle, Ariel, Lake Merwin, Yale Lake,
Cougar, North Bonneville, Stevenson, Carson, and Underwood
404 AM PST Fri Jan 10 2020

...VERY WET AND INCREASINGLY COLD WEATHER PATTERN FOR THE NEXT
WEEK, INCLUDING CHANCES FOR LOWLAND SNOW NEXT WEEK...

A long series weather disturbances will move across the Pacific
Northwest beginning Friday, and continues through much of next
week. These weather systems will bring periods of heavy snow to
the Cascades and the potential for moderate to heavy rain at lower
elevations through Sunday. Two significant cold frontal passages
are also expected, which will bring lowering snow levels from
Saturday night into next week, with an increasing risk of snow
reaching the valley floors next week.

Much colder air is expected to spread into southwest Washington
and northwest Oregon early next week, potentially cold enough to
bring snow levels down to the valley floor. While specifics on
accumulation amounts, areal distribution, and/or timing of snow
remain uncertain, we continue to have confidence in some risk for
low elevation snow next week. Now is a good time to make sure you
are prepared in the event that all of the necessary ingredients
come together for low elevation snows and associated travel
impacts during the middle part of next week.