Happy Valley, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

252
FXUS66 KPQR 031157
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
357 AM 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 nights, with
widespread stratus and fog across the central and south
Willamette Valley and also the Cowlitz and Lower Columbia River
Valleys of southwest Washington. Easterly flow through the
Columbia River Gorge continues to keep the Portland/Vancouver
metro mostly clear, although a small sliver of stratus is noted
moving up the Columbia towards the area as of 3 AM Tuesday.
Temperatures are dropping 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 today and
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 -7 mb will
maintain breezy conditions through the western Gorge through
Wednesday, producing wind gusts to around 30 mph at times in
eastern parts of the Portland metro and gusts as high as 60 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. /CB

&&

.AVIATION...High pressure and low level inversions continue to
bring air stagnation and minimal changes to the forecast.
Currently, LIFR conditions at KKLS, KUAO and southward, with VFR
conditions along the coast. KSPB, KHIO, KVUO, KTTD, and KPDX
currently have VFR conditions, but with low stratus moving from
the south and from the north through the Columbia River, will
likely see LIFR conditions develop at KSPB and KHIO by 12-13Z
Tuesday. Easterly flow through the Columbia Gorge will likely
keep KVUO, KTTD, and KPDX in VFR conditions. Looking ahead,
terminals in the central/southern Willamette Valley will likely
(80-90% chance) experience LIFR conditions through most of the TAF
period. Best chances to improve to VFR/MVFR will be between 22Z
Tuesday and 03Z Wednesday, as chances for LIFR lower from 80% to
20%. Considering last nights foggy conditions, there is low
confidence in central/southern Willamette Valley terminals
clearing during the aforementioned time.

In addition to the fog, at or below freezing temperature mean
that fog will freeze on surfaces. Cannot rule out a little rime
icing in locations where temperatures are the coolest. Note that
some terminals ASOS are reporting above freezing temps, but those
are the warmest in the region and highly localized. Winds through
the Columbia River Gorge and elevations within east/west aligned
terrain will continue to gust up to 30 to 40 kt, with some
elevated areas seeing up to 50 kt. There may be periods of speed
based wind shear, but have excluded from the TAFs due to winds
being unidirectional.

PDX AND APPROACHES...VFR with a 10-15% chance of IFR/LIFR fog
between 12-17Z Tuesday. Easterly approaches will see gusty
easterly winds. Surface winds will stay easterly and under 10 kt.
~Hall

&&

.MARINE...High pressure continues, keeping mild conditions over
all seas through at least Wednesday night. Winds will remain
under 10 kts and seas around 5 feet at 13 seconds until then.
Expect strong ebbs to return to the Columbia River Bar around 5PM
Tuesday, but with seas under 7 feet expected, will refrain from
issuing a Small Craft Advisory.

Early Thursday morning, a weak front passing through the area will
briefly elevate southerly winds, giving a 40% chance of Small
Craft Advisory criteria being met. Another round Friday through
Saturday will bring much higher chances of Small Craft Advisory
criteria being met as this system will elevate seas to around 10
feet. ~Hall

&&

.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 11 AM PST this morning 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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