High Wind and Strong Wind in Oregon, December 27, 2023

Area Forecast Discussion...Updated
National Weather Service Portland OR
937 PM PST Tue Dec 26 2023

Updated aviation discussion.

.SYNOPSIS...After a mostly dry day, will see rain spread across the
region late tonight and mainly Wed. Then, showery weather with snow
in the Cascades for several days. Another front will arrive Fri, but
looks to bring more of same with valley rain and mountain snow.
Temperatures will remain around that expected for late December.

&&

.SHORT TERM...(tonight through Thursday)...Mostly dry today, but
still on coolish side thanks to light offshore flow and more clouds
than sunshine. Broad low pressure remains offshore over the next
several days, maintaining moist southwest flow aloft. A series of
shortwaves will rotate around the low, but with the upper low fairly
stationary, these surface lows will track north to northeast between
long 130 and 133W, staying well offshore.

Low levels will remain to see offshore flow, keenly felt in the
Columbia River Gorge and areas near the Gorge, where moderate east
winds continue into Wed. Current cross-Cascades (Troutdale to The
Dalles) pressure gradient was about -5 mb (offshore, or east to west
flow through the Gorge). Models suggest this gradient could peak
around 9 to 11 mb later tonight. With that, should see breezy east
winds across good part of the metro (mainly West Hills of Portland
eastward to the Gorge), with those east winds gusting 20 to 35 mph.
But, in the west end of the Gorge, will see gusts 35 to 50 mph at
river level, and 65 to 85 mph (perhaps a few gusts even stronger) for
bit elevated areas, such as Crown Point and Corbett. Will not put up
any warnings, but travelers should be alert to occasional wind
buffeting their vehicles, especially RVs and trucks. Strongest winds
will be roughly 9 pm tonight until 8 am Wed.

Most of the region will remain dry tonight, as next system wraps up
offshore. Will have warm front lift northward this evening, with rain
along the coast and somewhat spotty rain farther inland. But, think
warm front will push rain well north of the region by midnight, with
dry conditions overnight. Will have areas of fog reform, though most
of that will be in the Willamette Valley from a Newberg to Canby line
southward.

Cold front will approach later tonight, with rain spreading back to
the coast by 4 to 6 am, and that rain spreading inland through the
morning. With temperatures in the upper Hood River Valley around or
just below freezing when rain starts Wed am,  precipitation will
start
as light freezing rain. But, any freezing rain in that area will be
light, and short-lived, as temperatures rise later Wed am. Even so,
areas in the Hood River Valley to west and south of Odell should be
prepared for some degree of icy roads for a time Wed morning.

Once cold front shifts inland, will transition to showers for the
afternoon. Should be enough instability aloft to support a few
thunderstorms along the coast and offshore. Will put such in the
forecast. Pattern rather stagnant for Wed night and Thu, as remain in
the showers. Though, could be more dry than showery by Thu afternoon,
as get bit more ridging inland. This due to next system beginning to
stand up offshore along long 132W (where front becomes more north to
south aligned). As such, any precipitation inland will be less, as
main frontal lift is offshore.		   /Rockey

.LONG TERM...(Friday through Monday)...Typical weather for late
December going into the weekend. Models cluster analysis maintains a
trough parked to our west/southwest, spinning repeated waves of
moisture towards us over the rest of the the week. Snow levels look
to remain at 5000 to 6000 feet for the majority of this period, but
NBM ensemble guidance looks very strong (65% chance) of snow levels
lower, running 3000 to 4500 feet by Monday. So, will maintain pattern
of showers, falling as snow across the higher terrain. But, overall,
accumulations do not look at that heavy.

&&

.AVIATION...Increasing southwesterly flow aloft tonight will
bring mid and high level clouds, while offshore flow strengthens
in the lower levels. Predominately VFR expected at most terminals,
except LIFR conditions have redeveloped at KEUG. It appears there
will be enough breaks in the mid to high level cloud cover and
light enough winds to bring a threat for fog and low cloud
development tonight in the rest of the central and southern
Willamette Valley, with around a 30-50% chance of IFR conditions
returning between 08-12Z Wednesday. Easterly winds out of the
Columbia River Gorge continue increasing with gusts up to 35-40 kt
possible at KTTD through Wednesday afternoon, beginning to weaken
with the next surface frontal passage. The next approaching front
will begin to spread rain to the coast after 12Z Wednesday and
inland after 14Z Wednesday.

PDX AND APPROACHES...VFR conditions expected to continue through
Wednesday with mid to high level clouds. East winds with gusts up
to 25-30 kt expected through Wednesday morning, decreasing as the
next front pushes through after 15z. Light rain likely after 15Z
Wednesday morning. -DH/HEC

&&

.MARINE...A strong low pressure system spreading northward across
the eastern Pacific will send a series of fronts across the waters
resulting in a prolonged period of Gale Force winds across the
outer waters. The Gale Warning to cover this hazard continues
through most of Wednesday night. It should be noted that there is
a 50% chance for Storm Force wind gusts of 50 kt to at least clip
the far outer waters (generally beyond 40-50 NM) tonight through
Wednesday night. The stronger winds occurring across the outer
waters should stay well offshore until Wednesday night when there
is a greater than 50% chance that Gale Force winds spread into the
inner waters.

This prolonged period of Gale to Storm Force S to SW winds to our
southwest will drive another large swell into the waters Wednesday
night. Latest wave guidance suggests seas will climb into the
23-25 ft range with a dominant period of 17 seconds Wednesday
night. This same guidance also suggests 16-20 hour period of seas
eclipsing 20 ft across the waters...mainly centered between 6 PM
Wednesday and 2 PM Thursday. Seas should then subside and fall
into the low teens on Friday.

However, another storm system will slide into the eastern Pacific
Friday into Friday night. This will keep winds elevated over the
waters although the probability of Gale Force winds drops from
50-70% early Friday across the outer waters to less than 10% by
early Saturday. Nonetheless, seas will likely climb back into the
mid teens Friday night into Saturday. A quieter weather pattern
early next week is looking like it will allow seas to drop below
10 ft. DH/Neuman

&&

.BEACH HAZARDS...Still have somewhat elevated seas, running 16 to 20
ft for Tue afternoon through Wed evening. While not high enough to
warrant a high surf advisory, it will maintain choppy and turbulent
surf conditions, along with enhanced sneaker wave potential. Will put
up a Beach Hazards statement to cover this danger.

A more substantial round of high surf will arrive later Wed into Wed
night, with seas 20 to 25 ft. Current model guidance places this
round near our advisory vs. warning criteria. Warning level criteria
historically has resulted more significant beach erosion events and
large waves impacting infrastructure along the coast. Will wait for
additional model runs before making a determination on which high
surf product will be more representative. Either way, sneaker waves
are always a significant hazard during high surf events. So, use
caution if you plan to be near the coastal surf zone.  /NeuRock

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...WA...None.
PZ...Small Craft Advisory until 1 PM PST Wednesday for Coastal waters
     from Cape Shoalwater WA to Florence OR out 10 NM-Columbia
     River Bar.

     Gale Watch from Wednesday afternoon through late Wednesday night
     for Coastal waters from Cape Shoalwater WA to Florence OR
     out 10 NM-Columbia River Bar.

     Gale Warning until 4 AM PST Thursday for Coastal waters from
     Cape Shoalwater WA to Florence OR from 10 to 60 NM.
&&

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland