High Wind Warning 4, NWS Portland, OR

Area Forecast Discussion
National Weather Service Portland OR
958 PM PST Sun Dec 24 2023

.SYNOPSIS...Typical late December weather expected for the rest of
this month. Low pressure over the Gulf of Alaska will bring a
front to the region Monday into Tue, with valley rain and
mountain snow. But, it will also bring freezing rain to the
Upper Hood River Valley tonight through Monday. Unsettled weather
will continues this week, with valley rain and mountain snow.
&&

.DISCUSSION...Sunday night through Tuesday...
Weak disturbance moved across region Sunday, with spotty light rain
and mountain snow. But, most areas remain dry and cool, with plenty
of clouds. Clouds will break up a bit more this evening, enough to
allow some cooling. Should see temperatures across region drop back
into the 30s for most areas, and upper 20s to lower 30s in Gorge.

A deep low pres (955 to 960 mb) is well offshore this afternoon, and
will track north to northeast into the Gulf of Alaska tonight and
Monday. As it does, the associated fronts will push across the Pac
NW. First to arrive will be the warm front. This warm front will
gradually lift northward across the region later tonight and Monday,
with rain spreading across Lane County around midnight tonight. That
rain will spread northward overnight, with a wet start to Monday.

Snow levels will jump as the warm front passes, from around 1500 to
2000 ft this evening, to around 6000 ft Monday am. As such, snow
accumulations in the Cascades will be limited. For now, generally, an
inch or two of snow possible on the passes, but any significant snow
will be only on the higher volcanic peaks, such as Mt Hood (Mt St
Helens), where could pick up 4 to 8 inches of snow tonight through
Monday morning.

Most concerning (and current forecast challenge) is the freezing rain
potential in the Columbia Gorge, Hood River Valley, and valleys in
the south Washington Cascades from Gorge to Indian Heaven Wilderness.
Models continue to support temperatures holding only at 29 to 32 deg
in those areas later tonight through Mon am, thanks to continued east
winds/offshore flow. With current rainfall expected, total ice
accumulations of 0.10 to 0.25 inch are expected in those areas, with
some potential of locally heavier accumulations. Such areas will be
the across the south and west sides upper Hood River Valley, where a
few spots could get as much as a third to half inch of ice. Final ice
accumulations will depend on temperatures. During the day, IF
temperatures are a few deg warmer than currently expected, will see
faster transition of the freezing rain to just rain (with only spotty
freezing rain). Ice accumulations closer to the Columbia River (along
I-84) will vary more, with 0.05 to 0.25 inch. Will see slow
moderation of temperatures along the Columbia River in the afternoon,
but will light freezing rain will continue in Hood River Valley as
well as farther north towards Carson and Indian Heaven Wilderness
into Monday evening. This will add a bit more ice. Will put up Winter
Weather Advisory for Freezing Rain for these areas (south Washington
Cascades, mid-Columbia River Gorge, and Hood River Valley), effective
from later tonight through Monday evening. Temperatures will warm
above freezing Mon night, ending the freezing rain potential.

Then, will see the cold front push rapidly across the region Monday
night into early Tuesday morning. Another round of rain, but with air
mass a bit more modified in/around mid-Columbia River Gorge,
precipitation in that area will mainly be rain, as temperatures
remain above freezing. Showers early Tuesday behind the front, but
does appear showers decrease quickly during the day. Would not be
surprised if have few if any showers for Tuesday afternoon. Snow
levels fall back down to around 4500 to 5500 ft.       /Rockey

.LONG TERM (Wednesday to Saturday)...
Another system offshore will push into the region on Wednesday. But,
front is getting stretched apart. As such, will see weakening lift.
Still, will be enough to provide light rain through the day. Snow
levels gradually lower to 3500-4500 feet for Thu. Rather active
weather pattern remains for rest of the week, with several fronts
lined up offshore. None look all that wet, so no heavy rain expected.
Just typical late December, with clouds, cool temperatures, and rain
at times.					   /Rockey

&&

.BEACH HAZARDS...There is also a high sneaker wave threat through
Friday. A series of developing low pressure systems across the
northeast Pacific this upcoming week will result in a series of
long period swells spreading across the waters at various points
in time. This will produce an extended stretch of a high sneaker
wave threat. The current Beach Hazards Statement looks on track.

Minor tidal overflow flooding is also expected for a few hours
around high tide along US-101 near Raymond, WA on Christmas Day.
Minor flooding (up to 1 foot above ground level) and erosion is
possible in the low lying areas near bays, sloughs, highway 101,
and the lower reaches of the coastal waters. A Coastal Flood
Advisory has been issued for the south WA coast from 9 AM to 1 PM
PST Monday to cover this threat. There is also the potential for
minor tidal overflow flooding again around high tide on December
26-27, however the forecast total tide is currently just shy of
meeting criteria for a Coastal Flood Advisory (total tide of 11.0
feet or higher is needed to warrant a Coastal Flood Advisory).

Lastly, a High Surf Advisory has been issued along the Oregon
coast and south WA coast, beginning 10 PM Monday. This is when
breakers up to 20 ft are expected to begin, lasting through at
least Tuesday night or Monday morning. Destructive waves may wash
over beaches, jetties, and other structures unexpectedly. People
can be swept off rocks and jetties and drown while observing high
surf. Minor beach erosion may damage coastal properties and
buildings. Higher than normal water run-up is expected on beaches
and low-lying shoreline.  -TK

&&

.AVIATION...As of 05z Monday, a surface warm front is
approaching the region with south to southwest flow aloft
associated with a weak upper trough that will push east of the
Cascades through Monday. The warm front will bring widespread rain
showers spreading north after 06z, likely reaching the PDX metro
area by 08-10z. Ahead of the front, widespread MVFR and low-end
VFR conditions have been observed and will continue until light
rain will cause MVFR/IFR ceilings through most of Monday. Winds
through the Columbia River Gorge will remain easterly and increase
after 12z. Winds elsewhere will remain generally offshore except
for southerly winds in the central and southern Willamette Valley.
After 14z, winds begin shifting southerly and increasing along
the coast. For inland areas, winds begin shifting southerly after
21z as a stronger cold front over the Pacific begins approaching
the coast.

PDX AND APPROACHES...Offshore flow will continue through the TAF
period with winds increasing after 08z. Expect sustained winds up
to 14-16 kts with gusts up to 25 kts. Low-end VFR to high end MVFR
ceilings will continue until the next warm front spreads light
rain into the area after 08-10z. This will lower ceilings over
the terminal, remaining in MVFR conditions through most of the TAF
period. -HEC

&&

.MARINE...Buoy 50 off Newport indicates steep and hazardous seas
with significant wave heights around 13 ft and a dominant wave
period around 13 seconds. In addition, southerly wind gusts of 25
to 30 kt developed across the waters Sunday afternoon ahead of a
cold front. Winds will temporarily subside Sunday evening once
the cold front passes before strengthening a lot more late Sunday
night into Monday morning. Confidence has increased that storm
force wind gusts of 50 to 55 kt will build across at least the
outer waters Monday afternoon into Monday evening, and a Storm
Watch remains in effect to cover this threat. Seas will respond
accordingly and build into the 18-23 ft range across the outer
waters and 15-20 ft over the inner waters during that time. A
stronger front is then forecasted to spread into the waters
Tuesday night into Wednesday. There appears more likely to be a
substantial gradient in forecasted wind speeds and seas between
50-60 NM off the coast and 0-10 NM off the coast during this time.
As a result seas will likely top 20 ft or higher across the far
outer waters while remaining in the teens near the coast.
Additional fronts and bouts of gale to storm force winds appear on
tap for the remainder of the week. The active weather pattern of
low pressures deepening well offshore will promote an environment
favorable for seas to push or exceed 20 ft at times next week.
-TK

&&

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