Lake Oswego, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

424
FXUS66 KPQR 192202
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
300 PM PDT Thu Mar 19 2026

.SYNOPSIS...A slow-moving cold front will move southeastward across
southwest WA and northwest OR Friday afternoon through Friday night,
bringing increasing chances for light rain late in the day, except
early in the day for the north OR coast and Pacific/Wahkiakum
counties. Isolated post-frontal showers Saturday morning will
diminish Saturday afternoon as surface high pressure builds into the
area under zonal flow aloft. This pattern will then hold steady for a
few days, bringing cooler and drier conditions Saturday afternoon
through Monday. A stronger Pacific cold front arrives sometime on
Tuesday, bringing widespread rain and breezy winds to the area. Snow
levels fall behind the front late Wednesday, however the bulk of the
precipitation associated with this system should be over with by the
time snow levels fall below the Cascade passes, most likely resulting
in minimal snow accumulation and travel impacts at the passes.

&&

.DISCUSSION...Now through Wednesday night...Satellite observations
from mid Thursday afternoon depicted increasing cloud cover from
north to south across the area, while radar observations showed
occasional light rain along and near the north OR coast and across
southwest WA. Light rain was in the vicinity of the Portland metro,
focused north of the Columbia River. Expect this trend to continue
through Friday morning before light rain begins spreading southward
across northwest OR Friday afternoon through Friday night along and
ahead of a cold front that will slowly push southeastward. Rain
amounts will be quite light in the Willamette Valley, with some
locations picking up only a trace to a few hundredths of an inch.
Meanwhile, rain amounts will be higher across southwest WA, the
Cascades, the north OR coast, and north OR Coast Range, albeit not
enough for flooding or notable impacts.

Models and their ensembles remain in agreement for surface high
pressure and zonal flow aloft behind the frontal passage for the
Saturday through Monday time frame. This will bring drier weather and
relatively cooler temperatures with highs close to average for this
time of year (mainly in the mid to upper 50s). Winds will also be
light, especially during the overnight hours each day. The light
winds will be in conjunction with clearing skies Saturday afternoon
into Saturday night, resulting in an ideal set-up for radiational
cooling. As such, forecast low temperatures remain coldest Saturday
night with widespread lows in the 30s. Areas of frost will likely
develop as a result. Those with sensitive outdoor potted plants
should consider bringing plants indoors for the night if possible, or
take precautions to protect vegetation from frost. Note NWS Portland
will not begin issuing Frost Advisories and Freeze Watches/Warnings
for agricultural purposes until April 1st when the growing season
begins to ramp up more and impacts from frost and freeze conditions
become more significant.

Confidence remains high for widespread rain and breezy winds Tuesday
into Wednesday as a stronger Pacific cold front moves inland, however
model ensemble guidance continues to show timing differences and
differences on exact precipitation amounts (however flooding is not
expected even in the wettest possible scenario). This front could
arrive as early as late Monday night or as late as Tuesday night,
with the most likely arrival time being sometime between Tuesday
afternoon and Tuesday evening. As a result of these timing
differences, the NBM 10-90th percentile for snow levels continues to
show large spread on Tuesday, ranging from 4500-9000 ft. However,
confidence is high snow levels will drop considerably behind the cold
frontal passage whenever that occurs, which would occur by Wednesday
evening at the latest. This is when even the NBM 90th percentile
suggests snow levels will be below the level of the Cascade passes,
while the 10th percentile drops to 500-100 feet. That being said,
ensemble guidance for QPF clearly shows precipitation beginning to
end by that time, meaning conditions will trend colder and drier with
little accumulating snow and travel impacts at pass level. NBMv5.0
probabilities for 6 inches of snow or more in a 48-hour period ending
at 5am PDT Thursday continue to back this expectation up, as chances
are only around 5-10% at pass level and near 0% below pass level.
Note lowland snow is NOT expected given conditions will be drying out
by the time temperatures become colder. -23

&&

.AVIATION...An upper level ridge to the south and a broad upper
level trough over the Gulf of Alaska continues to direct an
atmospheric river towards western Washington. The southern portion
of this atmospheric river will bring light rain showers along the
far north Oregon coast (KAST) through Friday. Can`t rule out a
few stray showers or sprinkles over the northern Willamette
Valley. High confidence (60-80% chance) that IFR/MVFR CIGs
persist at KAST at any given hour through the TAF period, while
the central Oregon coast (KONP) remains VFR through 09-11z Fri. By
11-12z Fri, the upper ridge will shift east and stratus will
increase southward along the coast as the atmospheric river shifts
slightly southward. After 12z Fri, there is high confidence
(60-80% chance) that IFR/MVFR CIGs will return to KONP and last
through the end of the TAF period.

Meanwhile, VFR conditions prevail for Willamette Valley terminals
with high level clouds through this evening. CIGs across the
Valley will gradually drop to around 5 kft or less Friday
morning as the upper ridge shifts eastward and troughing enters
the area. Winds generally southerly to southwesterly across the
area and under 10 kt, with occasional gusts up to 20 kt along the
coast.

KPDX AND APPROACHES...VFR conditions with high clouds through 12z
Fri. CIGs begin to gradually fall to low-end VFR after 09-12z Fri
as the upper level ridge shifts eastward. 30-40% chance for MVFR
CIGs between 2-3 kft at any given hour after 21z Fri. Southerly
to southeasterly winds under 10 kt. -10

&&

.MARINE...Low pressure offshore will maintain breezy southerly
winds through late tonight/early Friday morning, mainly for the
waters north of Cape Falcon including the Columbia River Bar. The
Small Craft Advisory for these waters remain in effect through 5
AM Friday for southerly wind gusts up to 25 kt. An exception is
the Columbia River Bar, where the Small Craft Advisory has been
extended through 8 AM Friday due to a strong ebb current around 6
AM which will build seas to 8-9 ft along the Main Channel of the
Bar. General seas for the rest of the waters are forecast around
7-8 ft at 10-11 sec.

Surface high pressure re-builds this weekend, turning winds more
northerly and remaining under 20 kt. Seas also gradually fall to
5-7 ft at 11 sec by late Saturday night into Sunday. Benign
marine conditions continue through Monday before another, more
robust system returns Tuesday into Wednesday. This system will
bring a return of breezy southerly winds across all waters.
Current guidance suggests moderate to high confidence (50-70%
chance) for widespread and frequent small craft wind gusts of 21
kt or greater, and a 10-20% chance for widespread and frequent
Gale force wind gusts of 34 kt or greater on Tuesday. Chances for
isolated Gale force wind gusts are around 50-70%. Seas on Tuesday
and Wednesday are also expected to build to around 13-15 ft in
response to increasing wind waves, with a 2-5% chance for seas
exceeding 20 ft. -10

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 8 AM PDT Friday for PZZ210.

     Small Craft Advisory until 5 AM PDT Friday for PZZ251-271.
&&

$$

www.weather.gov/portland

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