Happy Valley, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

469
FXUS66 KPQR 040551
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
951 PM PST Tue Dec 3 2024

.SYNOPSIS...High pressure over the region will produce dry
weather through at least Wednesday, with areas of clouds and
fog in the interior valleys and sunshine elsewhere. Rain chances
start to increase Thursday/Friday into the weekend with snow
levels remaining above the Cascade passes through Saturday.

&&

.DISCUSSION...Little change in the overall pattern as high
pressure persists over the region this morning. Satellite
imagery and surface observations from around the area paint a nearly
identical picture to the past several days, with widespread stratus
and fog across the central and south Willamette Valley. Easterly
flow through the Columbia River Gorge continues to keep the
Portland/Vancouver metro mostly clear. Temperatures dropped into the
20s with patchy frost formation being observed in a few locations
that are more sheltered from the wind. Expect more of the same
tonight into Wednesday as stratus and fog remain trapped in the same
areas beneath a strong subsidence inversion at around 1000 feet. Air
stagnation issues will persist in these area through Wednesday as a
result, with daytime temperatures continuing to struggle to get out
of the 30s in the central and south Willamette Valley. Meanwhile, a
TTD-DLS pressure gradient of -6 to -8 mb will maintain breezy
conditions through the western Gorge through Wednesday, producing
wind gusts to around 35 mph at times in eastern parts of the
Portland metro and gusts as high as 60-70 mph at favored locations
within the Gorge such as Corbett and Crown Point. This will also
continue to keep the Portland area under mostly sunny skies,
allowing afternoon temps to climb into the upper 40s each afternoon.

Medium range guidance continues to hint at some changes in the
pattern by Thursday as models are starting to come into better
agreement on the ridge weakening enough to allow a weak upper
level disturbance to cross the area on Thursday. It remains to
be seen if this will result in any precipitation returning to
the area as global ensembles have actually trended a bit drier
for Thursday and Friday in recent runs, but there are still
enough members depicting precipitation to keep a 20-30 percent
chance of rain inland and a 50-60 percent chance along the
coast for the latter half of the week. Regardless of how the
forecast unfolds, any impacts look to be minimal as QPF amounts
remain light and snow levels stay well above the Cascade
passes. At the very least, the passing disturbance will be
enough to weaken the subsidence inversion and finally put an
end to air stagnation issues while scouring the stratus and fog
out of the interior valleys. This will result in milder
temperatures for Thursday and Friday, with overnight low more
commonly in the upper 30s to low 40s as we head into the
weekend. The weekend will also bring increasing chances for
precipitation as the ridge axis finally shifts east of the
Cascades and allows an upper level trough to potentially
approach the region late Saturday into Sunday. DH/CB

&&

.AVIATION...Continued pattern of nightly fog at the central and
southern Willamette Valley terminals. Mixed IFR/LIFR conditions at
those areas will transition to full LIFR by 08z or so, continuing
for the rest of the night as thick fog remains in the area. Fog
likely lifts Wednesday midday around 18-20z Wed, but redevelops
Wednesday evening again. Less than 5% chance of fog reaching the
northern Willamette Valley terminals during this period.

With temperatures below freezing for much of the central and
southern Valley, freezing fog is expected to be a concern for any
terminals that will see fog. Rime icing will be possible in the
coolest areas.

Winds through the Columbia River Gorge continue to be strong, with
gusts up to 30-35 kts at times throughout the duration of the TAF
period. This should keep fog out of the north Valley.

PDX AND APPROACHES...VFR conditions with clear skies throughout
the period. Easterly winds under 10 kt at times due to strong
winds from the Columbia River Valley. /JLiu

&&

.MARINE...High pressure persists resulting in mild conditions
across all waters through at least Wednesday night. Winds will
remain under 10 kts and seas around 4 to 6 feet at 13 seconds.
Expect strong ebbs to return to the Columbia River Bar around 5PM
Tuesday and Wednesday with seas expected to be under 7 feet.

Early Thursday morning, a weak front passing through the area
will briefly elevate southerly winds, giving a 40%-60% probability
of Small Craft Advisory conditions. Another, stronger front on
Friday/Saturday will bring 50%-70% probability of Small Craft
Advisory conditions with seas building towards 10 feet on
Saturday and continuing to build into the mid to upper teens
(50%-60% probability) by late Saturday/early Sunday and will
likely remain in the low to mid teens for the start of next week.
/42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Air Stagnation Advisory until 4 AM PST Thursday for ORZ104-105-
     108-109-113>118-123>125.

     Freezing Fog Advisory until noon PST Wednesday for ORZ114>118.

WA...Air Stagnation Advisory until 4 AM PST Thursday for WAZ202-
     204>206-208.

PZ...None.

&&

$$

www.weather.gov/portland

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