Aloha, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

923
FXUS66 KPQR 221046
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
245 AM PST Sun Dec 22 2024

.SYNOPSIS...Another front moves across region today, with rain, then
showers tonight. Brief break for MON as most of the day should be
dry. But, rain spreads across region late MON afternoon into MON
night. Then showers again. Then, much wetter for WED through FRI, as
very wet frontal system slowly pushes across region. Will see snow in
the higher Cascades as well.
&&

.SHORT TERM...(Today through Tuesday)...
Yet another front will move across the region today. Front should
move to the coast by mid-afternoon, then across to the Cascades by 6
or 7 pm. Front will be bit wetter than the one that moved across
region on Saturday. As such, looks reasonable will get 0.25 to 0.50
inch across the region, with 0.75 to 1.25 inch across the Coast Range
and Willapa Hills as well as the Cascades slopes. Air mass will
destabilize behind the front with rain changing to showers. Will also
have a few isolated thunderstorms, with best chances being over the
coastal waters inland to the coast and coastal mtns. Showers
gradually decreasing overnight. Snow levels drop behind the front,
down to near 4500 ft tonight, with 2 to 6 inches likely.

Will get a brief break in the precipitation later for late tonight
through early MON afternoon. Expect areas of fog inland valleys,
mainly to south of Portland, with patchy dense fog from Salem
southward to Eugene into MON am.  Otherwise, increasing clouds MON.
Will see easterly winds pick up again, with gusts 25-45 mph in/near
the western Columbia Gorge in the afternoon/evening.

Next system is fast approaching, and will spread rain back to the
coast in the afternoon, and inland by late afternoon. Like past few
weather fronts, snow levels rise ahead of the front, with snow going
back above 6000 ft. Bit more rain with this front, but overall,
similar to rainfall that will see today (Sunday). That front will
push onshore later Monday night, then showers. Showers decreasing on
Tuesday. As cooler air behind the front spreads inland, snow levels
lower back to 3500 to 4000 ft. Snowfall of 4 to 9 inches expected
above 4500 ft, with 1 to 4 inches down to 3500 ft. /Rockey

.LONG TERM...(Wednesday through Saturday)...
Ensemble guidance continues trending towards another brief break
from precipitation during the day on Wednesday. Then ensembles
indicate a series of potentially stronger frontal systems will
impact the region late Wednesday into the end of next week,
though significant uncertainty remains between models in
moisture amounts and storm trajectory. The storm system
Wednesday night into Thursday still shows indications of being a
moderate to strong atmospheric river. NBM QPF for 48 hours
ending 4 AM Saturday over the coast, Coast Range, and Cascades
is 2-5 inches with 1.5-2 inches for the interior lowlands.
However, the high end 90th percentile scenario indicates up to
6-8 inches is possible over the Coast Range and Cascades with up
to 2.5-3 inches over the interior lowlands, and the low end
10th percentile scenario indicates only 1-3 inches over the
coast, Coast Range, and Cascades and 0.75-1.5 inches for the
interior lowlands. The best case and high end scenarios would
result in rises of area rivers, though with the significant
spread in the forecast, uncertainty remains in just how much
rivers could rise. Current probabilities indicate a 25-45%
chance of some rivers along the Coast Range reaching minor flood
stage as early as late Thursday, though more likely it would be
after the next weather system on Friday. Snow levels won`t start
has high Wednesday night, only around 4500-5500 ft, falling to
4000-4500 ft on Thursday. This will bring heavier snow to the passes.
Current forecast indicates around 1 foot of  snow is possible at pass
level through Friday, though the 90th percentile high end scenario
indicates up to 2 feet is possible. Wind will also be a concern with
these systems. NBM indicates a 50-70% chance of wind gusts over 50
mph along the coast Wednesday night through Friday with each frontal
passage, and a 25-50% chance of gusts over 40 mph inland. Keep an eye
on the forecast as these systems become better resolved. -HEC

&&

.AVIATION...Yet another wave of precipitation has begun to
slowly increase over the area this morning as a frontal system
tracks into the region. Rain will increase at all TAF sites as a
result with CIGs/VIS holding VFR to high-end MVFR this morning in
addition to an increase in southeasterly winds. Gusts up to 20 to
30 knots are anticipated along the coast and at KTTD. Once the
front through, coastal terminals see a 80% chance of MVFR cigs,
while inland TAFS see around a 25-45% chance of MVFR or lower
ceilings from around 00-06z Mon onwards.

PDX AND APPROACHES...Likely VFR conditions throughout most of the
TAF period. Rain moves in to the area this morning peaking midday
into the afternoon hours, with wind gusts increasing from the SE
during this time. Sporadic gusts up to 15-20 kt may be possible.
Around a 40-60% chance of MVFR cigs from 01-03z Mon onwards but
confidence in the exact timing of this change is only moderate.
-Schuldt

&&

.MARINE...Weather system after weather system will parade through
the coastal waters the week as a broad upper-level low holds in
place over the eastern Pacific. Our next frontal disturbance is
quickly approaching early this morning, expected to push over the
waters as the morning goes on leading to a rise in seas close to
18-21 feet this afternoon. High resolution guidance like the
HREF, HRRR, NAMNest, UWWRF, etc continue to favor the development
of high end Gales to Storm force gusts for all marine zones minus
the Columbia River Bar which will likely just see high end Gales.
Gusts between 45-55 kt are anticipated, highest for the outer
waters. HREF probabilities for gusts of 48 kt are greater then
80% for those outer waters marine zones while the NBM shows
little signal. However, it`s worth noting the NBM underperformed
with the last system that passed through on Saturday with the
HREF more accurately resolving max gusts - have continued to
hedge the forecast towards the HREF solution this forecast cycle
as a result.

Moving into Monday we`ll see the arrival of a long period swell
(~20 seconds) with significant wave heights likely peaking in the
20-22 foot range. After a lull of wave heights back into the
teens Tuesday into early Wednesday morning a stronger system mid
to late week will increase winds to at least Gales and usher in
seas near 20 feet yet again. The NBM now projects a 25-40% chance
for Storm Force (>48 knot) gusts on Wednesday across the outer
waters. Mariners should be prepared for continued hazardous
conditions through the end of the week into next weekend as the
active pattern continues. -Schuldt/Batz

&&

.BEACH HAZARDS...A large, energetic westerly swell will continue
to build over the coastal waters today into Monday. Seas in
excess of 18 to 20 feet with a period of around 19-21 seconds will
likely result in breaking waves approaching 25 to 30 feet in the
surf zone. The High Surf Advisory will be maintained through
Monday evening. Monday in particular will see the largest waves,
potentially approaching High Surf Warning criteria - still a
marginal setup with not enough confidence to upgrade the highlight
just yet. Continue to monitor future forecasts for changing
conditions. Beachgoers should be prepared for dangerous surf
conditions and large waves running far up onto the beach into
early next week.  -Schuldt/Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...High Surf Advisory until 10 PM Monday for ORZ101>103.

WA...High Surf Advisory until 10 PM Monday for WAZ201.

PZ...Gale Warning until 7 PM today for PZZ210.
     Storm Warning until 7 PM today for PZZ251>253-271>273.
&&


&&

$$

www.weather.gov/portland

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