111
FXUS66 KPQR 281814 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1014 AM PST Fri Feb 28 2025

Updated Aviation Discussion...

.SYNOPSIS...Expect quiet weather for the rest of this week as
high pressure brings mild and dry conditions with plenty of sunshine,
aside from some areas of morning fog. Weak low pressure will bring
light showers, cooler temperatures and cloudier conditions to the
area late Saturday into Sunday. Chances for light showers continue
Sunday night into Monday, mainly over the mountains.

&&

.SHORT TERM...Now through Sunday...The region will remain under the
influence of high pressure through at least Saturday morning,
bringing an extended period of dry weather with seasonably cool
overnight lows and warmer than normal high temperatures. Aside from
areas of fog for the coast and interior lowlands this morning, expect
another sunny day with light winds and widespread highs in the 60s
over the lowlands. Similar conditions are expected Saturday, albeit
temps will be a few degrees cooler both aloft and at the surface with
thin high clouds increasing late in the day from the west. These high
clouds will be associated with an upper level trough and attendant
weak surface low over the coastal waters. On Sunday morning, models
and their ensembles show this trough evolving into a broad cut-off
low before moving over northern California and southwest Oregon. The
surface low looks to move inland over the same general area,
indicating a vertically stacked low. The upper low is then set to
push ahead of the surface low into Nevada and Utah late Sunday into
Monday, indicating the low pressure system as a whole will be
weakening at that point.

The track of this low is set to bring the bulk of precipitation to
California and southwest Oregon, however there will be most likely be
some light and disorganized precipitation over northwest OR on the
northern periphery of this low beginning early Sunday morning. NBM
probabilities for precipitation peak Sunday afternoon at 75-90% for
the coast, Coast Range, southern Willamette Valley and Oregon
Cascades. Probabilities are lower from Salem to Portland/Vancouver to
Kelso, ranging between 50-60%. Locations that do see rain likely
won`t see very much; NBM probabilities for 0.25 inches of rain or
more are at 10-30% from 4pm Saturday-4pm Sunday across the lowlands,
except near 45% along the Oregon coast to the south of Seaside and
35-45% from Corvallis to Eugene to Cottage Grove. Probabilities are
highest in the Oregon Cascades and Coast Range, ranging from 45-65%.
Snow levels look to stay above pass level until late Sunday
morning/afternoon when snow levels look to dip to around 4500 feet.
Expect only 1-3 inches of snow above that.  -TK

.LONG TERM...Sunday night through Thursday night...A weak upper level
impulse on the backside of the aforementioned low pressure system is
set to move over northwest OR and southwest WA Sunday night into
Monday, bringing renewed chances for light rain showers, mainly in
the mountains as the valley will see some degree of rain shadowing.
Expect little to no impacts from both rounds of precipitation.
Chances for precip decrease on Tuesday in response to a transient
shortwave ridge, albeit not for long as there will be a shortwave
trough on the heels of this ridge with a decaying Pacific cold front
at the surface.

There is disagreement amongst model guidance from late Tuesday onward
in regards to the overall pattern, as some guidance suggests the cold
front and upper trough will decay rapidly upon moving inland,
resulting in mainly dry weather. On the contrary, some guidance shows
a relatively deeper trough with more showery activity over the area.
As of right now, the ENS/GEFS/GEPS only have a small handful of
members showing no precip at all, and the vast majority of ensemble
members have at least some light QPF. If precip does occur, it is
clear it will be light and mainly confined to the mountains as
forecast soundings suggest the Willamette Valley will see some degree
of rain shadowing on the leeward side of the Coast Range.

Attention then turns to a potential atmospheric river that looks to
take aim somewhere along the Washington and/or Oregon coast beginning
next Thursday night or Friday (March 6-7), bringing chances for
widespread rain. Confidence is very low regarding the track and
timing of this system. Currently the GEFS is trending drier for
northwest OR and southwest WA and wetter for northwest WA and
Vancouver Island, while the GEPS is trending wetter in northwest OR
and southwest WA. The ENS lies between these two solutions. There is
the possibility this system misses our area completely, which around
30% of current ensemble guidance shows, albeit most of the dry
solutions are evident in the GEFS rather than the ENS or GEPS. In
regards to the strength of this potential atmospheric river, IVT
plume forecasts from the GEFS/EPS generally show values peaking
between 250-500 kg/ms, indicating a weak atmospheric river. A small
handful of members do reach into the moderate category, but this is
not the most likely outcome at this time. This means overall hydro
impacts would likely be minor even if this system does hit the area,
which QPF guidance seems to support. That said, the forecast will
likely trend wetter or drier at some point leading up to this system
as confidence increases.  -TK

&&

.AVIATION...Another TAF period with stable conditions over the
airspace. Fog and low stratus this morning continues to clear out,
with conditions likely improving to VFR by 19-20Z Friday. With
light winds and stable conditions through today, more fog and low
stratus is possible tonight. Along the coast, LIFR fog conditions
are expected to return around 06-08Z Saturday, with development as
early as 04Z for KAST. Expected these conditions to persist
through the TAF period, beginning to improve by 18-20Z Saturday.
For the inland valleys, expect LIFR fog conditions to develop
around 08-12Z Saturday, persisting until around 18-20Z Saturday.
Probabilistically, chances for LIFR conditions are around 20-40%,
highest along the coast and lowest within the inland valleys.

PDX AND APPROACHES...MVFR conditions continue to improve, so
expect VFR conditions by 19-20Z Friday. Will be VFR through most
of the day, then a return to LIFR fog around 08-12Z Saturday
(20-30% chance of LIFR). Otherwise, light winds shift easterly
around 04Z Saturday.                               ~Hall

&&

.MARINE...A mid-period westerly swell continues to maintain seas
around 10 to 12 ft, though seas will briefly come down to 8-10 ft
Friday late afternoon. Afterwards, another system arrives that
brings combined seas back up to 12-14 ft by Saturday morning.
Small Craft Advisory continues through Friday morning for all
coastal waters. The Columbia River Bar sees some stronger than
normal ebb currents; combined with elevated seas, have decided to
extend SCA for the Columbia Bar through Saturday morning.

Another weak weather system will approach the waters Saturday
into Sunday, with a longer period swell arriving by early
Saturday, building seas to around 12 to 14 ft. At present, only
around a 10-30% chance of max 24 hr wind gusts on Saturday
reaching Gale critera. Seems more likely to be a higher-end Small
Craft situation. /JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 10 AM PST Saturday for PZZ210.
&&

$$

www.weather.gov/portland

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