High Wind in Oregon, January 2 to 3, 2021

Area Forecast Discussion UPDATED
National Weather Service Portland OR
1001 AM PST Sat Jan 2 2021

...UPDATED, for morning aviation discussion.

.SYNOPSIS...The first few days of 2021 will be wet, mild, and
occasionally windy, but with plenty of snow expected for the ski
resort elevations. Aside from the above normal temperatures, not all
that far off from what one would expect this time of year in the
Pacific Northwest. Our latest front is pushing a swath of rain
eastward across the forecast area this afternoon and evening. Rain
and southerly winds increase Saturday as a stronger front pushes
onshore from the NE Pacific, continuing Saturday night before
tapering to showers Sunday. Little rest for the rain-weary through at
least Monday as a parade of frontal systems moves across the Pacific
Northwest.

&&

.SHORT TERM...Today through Monday Night...A strong westerly upper
level jet over the northern Pacific with a core speed up to 160 kt
is directed at the Washington/Oregon coast driving a plume of deep
moisture toward western Washington and northwest Oregon. Expect rain
to increase across the region today. Heaviest rainfall rates are
expected across far northwest Oregon and southwest Washington,
especially along southwest facing slopes of the Willapa Hills, north
Oregon coast range, and south Washington Cascades. Rainfall
accumulations in these areas of 2 to 4 inches likely with locally
higher amounts up to 6 inches possible over a 24 hour period. Minor
flooding along the Grays River near Rosburg will be possible late
Sat night and Sun morning.

The surface front will undergo frontogenesis this afternoon with
very strong southerly winds developing along the coast. The High
Wind Warning continues to look on track beginning at noon today as a
coastal jet sets up. South wind with gusts up to 65 mph is expected
at coastal towns and other areas away from the beaches and
headlands. But, more exposed beaches and headlands could see gusts
as high as 75 mph.

Winds are expected to increase through the Willamette Valley and
greater Vancouver area later this afternoon as the front slowly
slides south. But, think strongest winds will be across the
Willamette Valley, for areas south of Portland. Peak gusts over
interior lowlands generally this evening, with 25 to 35 mph across
Portland/Vancouver metro area, with 30 to 45 mph for areas to south
of Portland. The front will continue its southward slide as an upper
shortwave riding along the jet stream approaches the Pacific NW
coast. The moisture plume will then pick up its step and slide
across the rest of the CWA overnight with the heavier rainfall rates
likely after midnight through the Willamette Valley and Oregon
Cascades. Winds will also quickly diminish later tonight, especially
after midnight as the front passes.

Heavy, wet snow is also expected with this weather system, mainly
above 5000 feet in the Cascades. Snow levels around 4500 feet will
rise to around 5000-5500 feet this evening and tonight. Have issued
Winter Weather Advisories for the Cascades from southwest Washington
to the northern and central Oregon Cascades during the times we
believe the snow rates will be the heaviest. Expect to see total
snow accumulations of 6 to 12 inches through the northern Oregon
Cascades, with locally higher amounts possible over the south
Washington Cascades. Snow levels will quickly fall behind the front,
as will the precipitation rates.

By Sunday morning the front will have exited the region, stalling
across southern Oregon. Another upper shortwave and associated
frontal system will approach Sun morning. This system will absorb
the stalled front and begin to lift north by Sun afternoon.
Precipitation ahead of the warm front will spread from south to north
across western Oregon into southern Washington Sun evening. Snow
levels around 3000-3500 Sun morning will rise again through the day.
As QPF increases snow levels will rise to around 5000-5500 feet Sun
night. Expect another round of strong southerly winds along the
coast Sun night as well. The system becomes somewhat more
interesting Monday as part of the shortwave splits and dives
southeast. This leaves us with some uncertainty in the forecast, but
it does appear the weather should continue to be wet and mild
heading into next week.

The long period (18-19 seconds) westerly swell is expected to build
early this morning then last into the afternoon before slowly losing
energy as the dominant wave period drops to 16 to 17 seconds. This
supports keeping the High Surf Advisory for today, and also brings
an enhanced threat of sneakers waves. /DDH

.LONG TERM...Tuesday through Friday...The active weather pattern
continues into next week as a series of additional systems are very
likely to impact the Pacific Northwest. Ensemble models continue to
show good agreement in a mean trough persisting over the Pacific
Northwest through the week. A brief period of mainly dry weather
will be possible through Tuesday afternoon before the next front is
likely across the region Tue night into Wednesday. Multiple
shortwaves will continue across the Pacific in what seems a never
ending parade. Freezing levels will continue to oscillate between
3000 to 6000 feet as these systems traverse the area. Generally
expect wet and possibly windy conditions, along with snow in the
Cascades, to persist through much of next week. /DDH

&&

.AVIATION...VFR inland, with MVFR along the coast this am. MVFR
conditions will spread inland across the north interior through 21Z,
and to south later this afternoon as a strong cold front approaches.
Rain will increase this afternoon, contributing to the increased
MVFR in clouds and vis. Rather strong pressure gradients for this
afternoon and evening ahead of the front. Southerly winds gusting 50
to 60 kt along the coast, with strongest this evening. Winds farther
inland gusting 25 to 35 kt for airports across Willamette Valley.

Cold front will push to the near Astoria by 05Z, and to a KONP to
KPDX line by 07Z, then on the far southeast Lane County by 09Z. Will
see rapid decrease in winds behind the front. Flight conditions will
gradually improve, but think will maintain MVFR CIGS on into Sun am.

For detailed regional Pac NW weather information, go online to:
http://weather.gov/zse

KPDX AND APPROACHES...VFR at moment, with occasional MVFR CIGS. As
rain increases, and front draws bit closer, will see MVFR becoming
dominant between 21Z and 23Z. Breezy with MVFR and rain through the
evening, with peak gusts near 30 kt. Front will push across OPS area
between 06Z and 07Z, with winds easing. But, stays MVFR overnight.
Rockey

&&

.MARINE...A very active weather pattern will continue through early
next week, keeping seas high while bringing periodically bringing
gale force winds to the coastal waters. Seas over the next few days
will tend to be dominated by a rather long period westerly swell.

South winds will strengthen today in advance of a cold front that is
expected to move quickly southeast across the waters tonight. Expect
winds to increase to gale force today, and by this evening peak
gusts appear likely to approach storm force before winds turn to the
northwest and decrease later in the night. The front is expected to
reach the coast at the mouth of the Columbia around 8 PM this
evening, and move down to Newport by about 2 AM. The strong
southerly winds will generate a steep windwave and fresh swell today
and tonight, that coupled with a long period west swell running
between 17 and 22 ft will make for especially chaotic seas.

Sunday appears likely to bring a short break in the winds as a weak
ridge of high pressure moves across, but a large westerly swell will
continue. Sunday night into early Monday another frontal system
brings strengthening southerly winds, likely reaching gale force or
possibly storm force again. As with the previous system, large west
swell coupled with locally driven wind waves and fresh swell will
build chaotic seas on the order of 20 ft or better Sunday night.

The active weather pattern continues early next week, with another
strong front expected to arrive late Tuesday or Tuesday night.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 PM this afternoon to 4 AM PST
     Sunday for Northern Oregon Cascades.

     Winter Weather Advisory from 10 PM this evening to 10 AM PST
     Sunday for Cascades in Lane County.

     Wind Advisory from 4 PM this afternoon to midnight PST tonight
     for Central Willamette Valley-Greater Portland Metro Area-
     South Willamette Valley.

     High Surf Advisory until 4 PM PST Sunday for Central Oregon
     Coast-North Oregon Coast.

     High Wind Warning from noon today to 1 AM PST Sunday for
     Central Oregon Coast-North Oregon Coast.

WA...Winter Weather Advisory until midnight PST tonight for South
     Washington Cascades.

     Wind Advisory from 4 PM this afternoon to midnight PST tonight
     for Greater Vancouver Area.

     High Wind Warning from noon today to 9 PM PST this evening for
     South Washington Coast.

     High Surf Advisory until 4 PM PST Sunday for South Washington
     Coast.

PZ...Storm Warning from 6 PM this evening to 1 AM PST Sunday for
     coastal waters from Cape Shoalwater WA to Florence OR out
     60 NM.

     Gale Warning until 6 PM PST this evening for coastal waters
     from Cape Shoalwater WA to Florence OR out 60 NM.

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

&&

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