Lake Oswego, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

780
FXUS66 KPQR 201100
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
300 AM PST Sat Dec 20 2025

.SYNOPSIS...The region remains locked in a cooler, showery, and
unsettled airmass through the weekend with some of our slower
responding rivers like the South Yamhill, Pudding River at
Aurora, etc. holding onto river flooding impacts. Across the
Cascade passes snow showers will allow winter travel conditions
to persist, although given the sad state of our snowpack, snow
levels around 2,500-4,000ft aren`t unwelcome in that regard.
Otherwise, expect a fairly active and progressive weather
pattern through next week.

&&

.SHORT TERM...Now through Sunday Night...This morning scattered
showers remain ongoing across the region as we sit in a cooler post-
frontal airmass with broad zonal flow aloft. Exploring traffic
cameras highlights the winter-like driving conditions in place across
the mountain passes early this morning with snow showers
continuing above 2500-3000ft today, most frequent before noon
and in the north Oregon/south Washington Cascades. Come the
midday hours into the afternoon, models show slowly building
heights aloft thanks to the axis of a weak/subtle longwave ridge
feature progressing through Oregon leading to a decrease in
showers, especially in the central Oregon Cascades and
Willamette Valley. In any case prepare for winter-like driving
conditions if you plan to traverse across the mountain passes.
Across the lower elevations showers will provide additional
rainfall but likely not enough to result in in urban and small
stream flooding outside of some extremely localized impact in
the event of showers training over the same locations for an
extended period of time. Still, for a handful of our rivers
flooding is still continuing as all the water from this past
week`s atmospheric river works its way through the river
systems. For more details on ongoing river flooding concerns,
please read the hydrology discussion below.

By late Saturday, models and their ensembles continue to show
westerly flow aloft shifting west-southwest Saturday night into
Sunday morning, before becoming southwesterly Sunday afternoon.
This will be in response to a trough over the Pacific nearing
the Washington/Oregon coast, which is set to push inland Sunday
evening/night. While scattered showers will persist across the
area on Saturday and Sunday ahead of this trough, the bulk of
the heaviest precipitation this weekend will occur Sunday
evening/night with passage of this trough feature. Not
expecting much in the way of impacts with this system, aside
from additional travel impacts over the Cascade passes. From
4am Sunday through 4am Monday, the NBM suggests there is a 45%
chance for 6 inches of snow or more at Willamette Pass, a 60%
chance at Santiam Pass, and a 40% chance on highway 26 near
Government Camp. Should these probabilities increase, a Winter
Weather Advisory will likely be needed as the forecasted snow
totals are right on the cusp of warranting one. Probabilities
for 12 inches of snow or more are much lower at 8-20%. -99/23

.LONG TERM...Monday through Friday...Overall there remains
fairly good agreement between the GEFS/GEPS/ENS ensembles
system regarding the synoptic scale pattern to at least start
the long term with a broad upper level troughing at 500 mb over
the northeastern Pacific showing very little movement. However,
a series of shortwave troughs rotating around this broad
longwave trough are set to swing into the U.S. West Coast from
the south/southwest, bringing continued chances for showers over
northwest OR and southwest WA almost every 24-48 hours next
week. There is now high confidence one of these shortwaves
arrives the second half of Monday into Monday night. In addition
to increasing showers, breezy south winds will accompany this
system. Max wind gust guidance from EPS suggests wind gusts will
likely peak between 20-35 mph inland and between 35-55 mph at
the coast - an increase from earlier model runs. We`ll need to
watch this trend closely this weekend. NBM 24hr max gust
chances to exceed 45 mph are generally 0-5% across the interior
lowland but 40-60% at the coast suggesting wind impacts will be
fairly limited to the latter region in coverage.

By the middle of the week the aforementioned upper level trough is
expected to transition into a closed low while retrograding and
dropping southward leaving us in board southerly flow. From this
point onward, forecast uncertainty significantly increases as
model guidance struggles to resolve the placement of this broad
closed low and attendant shortwave troughs swinging in from our
south/southwest. The vast majority of ensemble guidance
continue to show the area of heaviest rainfall and strong winds
well to our south in California. However, a decent clustering
of 18z and 00z EPS members now bring a potent surface low
feature up through California into western Oregon on Wednesday,
so we may not be out of the woods regarding additional wind and
rain related impacts. By the end of the week, ensemble means
finally progress the this large closed low feature into
California and place weak ridging overhead - we`ll have at
least a shot at a dry day late next week into the weekend. In
any case, given the dynamic nature of the forecast confidence
in our weather-related impacts are low Wednesday onward. -99/23


&&

.AVIATION...Widespread VFR with showers expected across the
airspace. Headed through the morning conditions will likely
trend towards a high-end MVFR/low-end VFR holding here through
the remainder of the TAF period. Westerly winds will stay more
southerly across the air space up 10-15 kt sustained. Expect
gusts along the coast up to 25 kt starting around 17Z Saturday
and gusts up to 20 kt a few of the inland sites. It`s worth
noting there is a a 15-25% chance for Thunderstorms along the
coast through the TAF period. Any thunderstorms could produce
locally gusty winds, small hail, and infrequent lightning.

KPDX AND APPROACHES...Generally VFR conditions through the TAF
period although chances for MVFR CIGs increase this morning to
30-40%, mainly coinciding with shower activity. At least the
probability for IFR CIGs/VIS today is low, only around ~5%.
-99/42

&&

.MARINE...Conditions will slowly subside through tonight and
into tomorrow, which will cause sustained winds to decrease
towards 8 to 10 ft with gusts up to 25 kt through Saturday.
Therefore, will maintain a small craft advisory across all
waters and the Columbia River Bar. There is also a 10-25%
probability for thunderstorms across the Columbia River Bar and
coastal waters at times through the weekend as well. Any
thunderstorms could result in brief erratic winds, heavy rain,
and lightning. South winds will persist into next week as a
series of fronts move across the waters. A fresh west swell will
result in seas building above 10-12 feet again on Monday. Seas
are likely to continue to build periodically through next week
in additional to bursts of breezy winds accompanying the
aforementioned frontal systems moving through the region.
-99/42

&&

.HYDROLOGY...Although heaviest rain has ended over the area and
we`ve transitioned to showers, widespread minor to isolated
moderate river flooding continues. As of early this morning, the
Luckiamute River near Suver remain at moderate flood stage.
Meanwhile, the following rivers remain in minor flood stage:
the Cowlitz River at Kelso, the Marys River near Philomath, the
Pudding River at Aurora, and Gales Creek near Forest Grove. Most
rivers are forecast to fall below flood stage later this
morning, aside from the Luckiamute River which is forecast to
fall below flood stage Sunday, and the Pudding River which is
forecast to fall below flood stage on Tuesday. The latest river
forecasts across the region can be found at:
www.water.noaa.gov/wfo/pqr. Be sure to never drive through a
flooded road and heed any lingering road closures.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST this morning for
     ORZ126-127.
     Winter Weather Advisory until 4 AM PST early this morning for
     ORZ128.
WA...Winter Weather Advisory until 10 AM PST this morning for
     WAZ211.
PZ...Small Craft Advisory until 10 PM PST this evening for PZZ210-
     251>253-271>273.
&&

$$

www.weather.gov/portland

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