Aloha, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

358
FXUS66 KPQR 220551
AFDPQR

Area Forecast Discussion...Updated Aviation
National Weather Service Portland OR
950 PM PST Sat Dec 21 2024

.SYNOPSIS...Rain showers this afternoon with a slight chance of
coastal thunderstorms. Next front brings rain for Sunday, and
showers Sunday night into Monday. Most of the day on Monday
looks to be dry, but rain/showers again later Monday night into
Tuesday. Then, a rather wet and breezy Christmas day, with rain
and breezy weather continuing through Friday.

&&

.SHORT TERM...Today through Monday Night...A bit of a rinse and
repeat pattern is in store this weekend into next week as
multiple short-fused frontal systems move through the PacNW.
Scattered showers are being observed on radar across NW Oregon
and SW Washington this afternoon as the cold front that moved
through the region this morning is now situated over eastern
Oregon. A few thunderstorms have been observed along the coast
and inner waters over the past couple of hours. A 15-20% chance
of thunderstorms continues in these areas this afternoon, ending
after sunset. Snow levels over the Cascades are beginning to
fall in the post- frontal cold air, with snow levels around
4000-4500 ft expected through the overnight hours into early
tomorrow morning. However, since precipitation will remain
mostly showery and light during this time period, snow amounts
will be limited to around 1-3 inches at pass level.

Most areas will see a break in the precipitation this evening
into early tomorrow morning before the next frontal system moves
into the region. Light scattered rain will spread across the
region early tomorrow morning from the south with the warm
front, which will also increase snow levels over the Cascades
again to 6000-7000+ ft by late morning. As the cold front
approaches the coast by late morning, another round of
widespread rain will quickly spread inland through the late
morning and afternoon hours with scattered showers behind the
front late afternoon into the evening hours. Additional QPF is
similar to today`s forecast with around 0.25-0.5 inches for the
lowlands and 0.75-1.5 inches over the terrain, locally higher
possible in stronger showers. Snow levels will once again fall
to 4000-4500 ft by Monday morning, but conditions will be mostly
dry by then leading to even less snow.

Monday is expected to be mostly dry before yet another frontal
system moves into the region Monday evening through Tuesday.
Similar to previous systems, snow levels will begin above pass
level (6000-7000+ ft), falling in the post-frontal cold air
Tuesday morning to around 4000-4500 ft and down to 3000-4000 ft
Tuesday evening. Ensembles indicate there could be a touch more
moisture associated with this system, with QPF 0.5-1 inch for
the lowlands and up to 2 inches over the terrain. The Cascade
passes could see another 1-4 inches of snow with flurries down
to 3000 feet.

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 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 during the day 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...Showers have mostly tapered off throughout the region,
and winds have generally calmed to be less than 8 kts throughout
the region. Ceilings are predominantly VFR, though some occasional
bursts of MVFR remain possible through around 8z Sun,
particularly at the coast. The next wave of moisture moves in
between 13-17z Sun, bringing rain back to the region, as well as
elevated southeasterly winds. Gusts up to 25 kt will be possible
after that time through the rest of the TAF period at all
terminals. Once the front moves through, coastal terminals see a
80% chance of MVFR cigs, while inland TAFS see around a 30-40%
chance of MVFR or lower ceilings from around 01-02z Mon onwards.

PDX AND APPROACHES...Likely VFR conditions throughout the TAF
period. Rain moves in to the area around 15z Sun, with wind gusts
picking up from the SE around that time. Gusts up to 18-20 kt may
be possible at that time. Around a 30% chance of MVFR cigs from
01-02z Mon onwards, but likely remains VFR. /JLiu


&&

.MARINE...Going through the next week a very active weather
pattern is anticipated as a broad upper-level low remains parked
over the NE Pacific aiming a parade of weather disturbance at the
Pacific Northwest. Steep seas with heights in the mid to upper
teens and period around 12 to 15 seconds. Seas may decrease a few
feet into the mid teens tonight but will jump back up into the
upper teens with the next frontal system on Sunday. Hi-res
guidance (HRRR, NAMNest, UWWRF) are showing good agreement in
Storm force gusts for all marine zones (minus the Columbia River
Bar which will see high end Gales) beginning late tonight and
continuing through SUnday afternoon. Frequent gusts between 48-60
kt expected. HREF probabilities for gusts of 48 kt are greater
then 60% while the NBM shows little signal. However, the NBM
underperformed with the latest system that passed through earlier
Saturday morning with sporadic gusts greater than 48 kt. Given
this trend, have hedged toward the higher res models and HREF
probabilities.

Moving into Monday we`ll see the arrival of a long period swell
(~20 seconds) with significant wave heights likely peaking in the
low 20s. After a lull 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 currently
projects a 20% chance for Storm Force (>48 knot gusts) in the
Wednesday afternoon through Thursday time period too - something
to watch. Mariners should be prepared for continued hazardous
conditions through the end of next week.
-Batz/Schuldt

&&

.BEACH HAZARDS...A large, energetic westerly swell will build
over the coastal waters and begin impacting the coastline Saturday
into early next week. 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 for Saturday morning through Monday
evening. Monday in particular will see the largest waves,
potentially approaching High Surf Warning criteria, although there
isn`t enough confidence in degree of wave energy required to
upgrade the highlight as of this forecast cycle. A slight
increase in either swell height/period would push energy values
to warning criteria. 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
beginning late Sunday and continuing through early next week.
-Schuldt/Batz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

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

PZ...Hazardous Seas Warning until 2 AM PST Sunday for PZZ210-251>253-
     271>273.

     Gale Warning from 2 AM to 7 PM PST Sunday for PZZ210.

     Storm Warning from 2 AM to 7 PM PST Sunday for PZZ251>253-
     271>273.
&&

$$

www.weather.gov/portland

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