980
FXUS66 KPQR 092137
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
237 PM PDT Sun Mar 9 2025

.SYNOPSIS...A slow moving front will bring light rain to inland areas
Sunday evening/night. Rain tapers off Monday morning. The weather
pattern then becomes more active and progressive, resulting in a
prolonged period of cool and wet conditions from Tuesday onward with
several rounds of valley rain, mountain snow, and breezy winds.

&&

.DISCUSSION...Now through Saturday night...At 1 PM Sunday, light
stratiform rain had finally begun along the south WA and Astoria
area, arriving a few hours later than initially expected due to the
very slow-moving nature of the frontal boundary associated with this
precipitation. As such, the expected start time for rain to begin is
now a few hours later for the rest of the area as well. The latest
12z iteration of the HREF seems to have caught onto this delay well,
reflecting current radar observations accurately. The most likely
start time for light rain to begin has shifted to 4-5pm Sunday on the
central Oregon coast from Tillamook to Florence, 5-6pm Sunday in the
Cowlitz Valley and lower Columbia, 8-10pm for the Portland/Vancouver
metro and central Willamette Valley, and midnight-3am Monday for the
southern Willamette Valley. Although precipitation intensity will be
light, forecast rain amounts have increased slightly in some
locations due to the slow movement of the aforementioned frontal
boundary. The NBM is now showing a 70-90% chance for over 0.25" of
rain by 11am Monday, except a 30-40% chance in Eugene-Springfield,
Cottage Grove and Creswell. No hydro impacts are expected with this
rain as precip rates and total rain amounts remain much too light for
flooding concerns, despite the slight uptick in QPF.

Precipitation will gradually wind down Monday morning as the front
dissipates over northwest Oregon. Once rain ends Monday, expect
mainly dry conditions to continue Monday night into Tuesday morning.
That said, 500 mb flow will back from westerly to southwesterly ahead
of a slow-moving trough approaching the coastal waters. At the
surface, the deterministic GFS/EURO/NAM/Canadian all show a
weak/elongated surface low moving northward over the coastal waters
towards Vancouver Island late in the day. Although the center of this
low will not make landfall in northwest OR or southwest WA, a warm
front associated with this low will move inland and lift northward
over the area late in the day Tuesday. This will bring another round
of light stratiform rain to the area late Tuesday into Wednesday,
following by a cold frontal passage late Wednesday with post-frontal
showers expected Wednesday night through Thursday night. Note
precipitation will fall in the form of snow in the Cascades during
that time, and eventually for upper elevations in the Coast Range,
Upper Hood River Valley and Cascade Foothills as well (most likely by
Thursday night/Friday morning when snow levels will likely bottom out
around 1000-1500 feet). This will result in accumulating snow at
elevations lower than usual for this time of year, bringing travel
impacts to the highest portions of highway 26 in the Coast Range in
addition to the Cascade passes. Although forecast 6-hr snow amounts
in the mountains are not overly impressive from now through Thursday
night, that begins to change late Friday through Saturday night.

This is when a more potent low pressure system is set to arrive,
bringing more notable impacts to the area. This system will bring
heavier rain in the lowlands and periods of heavy snow in the
Cascades. 24-hr snow amounts from 5pm Friday to 5pm Saturday will
likely exceed one foot for the Cascade passes (60-80% chance, except
a 30-40% chance on highway 26 near Government Camp). Additional
Cascade snow is expected after 5pm Saturday, potentially another foot
or more. This will result in very hazardous travel conditions at pass
level, and forecast snow amounts are more than enough to warrant an
eventual Winter Storm Watch if the forecast holds over the next few
days. For the lowlands, not expecting much in the way of impacts at
this time as rain does not look heavy enough to suggest flooding will
be a concern. However, there is the potential for strong winds in the
lowlands, which could result in downed trees and power outages if
some of the windiest model ensemble solutions were to verify.
Ensemble members from the EPS and GEPS are picking up on the wind
potential. However, uncertainty is high as the outcome will be
dependent on the exact strength and track of a surface low that will
be moving inland. For now, there is a 10-20% chance for max wind
gusts over 45 mph between 11pm Friday and 11pm Saturday, except
around 50% at the coast and 60-80% for upper elevations in the Coast
Range and Cascades. Will need to see if these probabilities increase
or decrease over the coming days to determine if wind damage is worth
messaging. -TK

&&

.AVIATION...An incoming slow moving cold front is beginning to
push through the area, already impacting the coast, reaching
inland areas around 0-2z Mon. The coast is already seeing MVFR
cigs, and inland areas can expect ceilings to lower at that time.
90%+ confidence in MVFR cigs at that time, with 30-40% chance of
IFR cigs at all terminals. MVFR cigs last through at least 18-20z
Mon. Expect precipitation at times that could temporarily reduce
visibility at times, particularly in the first few hours of
frontal passage.


Breezy southerly winds are in place, particularly at the coast,
which is currently seeing gusts up to 35 kt. Inland terminals
are seeing closer to 20-25 kts, and elevated winds remain through
the next few hours. After the front fully pushes through, winds
will turn westerly and weaken drastically to below 10 kt by 5z
Mon.

PDX AND APPROACHES...Current VFR conditions will degrade to MVFR
around 4z Mon, when a slow moving cold front passes overhead.
90%+ confidence in MVFR cigs or lower, with only a 30% chance of
IFR cigs at times during frontal passage. Rain expected once the
front fully moves overhead. Southerly winds expected before the
frontal passage, with gusts up to 20-25 kt possible. Once the
front passes through, expect more mild southwesterly winds under
8 kt. /JLiu

&&

.MARINE...A weak cold front is currently passing through the
coastal waters, bringing gusty winds and increased wind waves.
Winds are generally south to southwest at 15 to 20 kt with gusts
up to 30 kt. Winds thus far have remained just below Gale
criteria, and the Small Craft Advisory remains on track. While
winds will be decreasing throughout the rest of this afternoon, seas
remain right around 10 feet through Sunday night at 12 seconds.
As a result, the Small Craft Advisory continues out through the
end of Monday night. As the front exits the area, conditions will
become less active with winds easing to 10-15 kt and seas around
6-9 ft at 13 seconds.

The pattern remains stagnant until Tuesday night when another
frontal system arrives with the potential for another round of
strong winds and elevated seas. Current ensemble guidance puts
chance of Gales around 20% for that system, with seas around 10 ft
at 14 seconds. -Muessle/JLiu

&&

.BEACH HAZARDS...A high sneaker wave threat continues along the
coast today as cold frontal system brings a 10-12 foot westerly
swell with a period of 14-15 seconds. Therefore, a Beach Hazards
Statement remains in effect until 5 AM Monday.

Waves can run up significantly farther on a beach than normal,
including over rocks and jetties. Sneaker waves can suddenly knock
people off of their feet and quickly pull them into the frigid
ocean, which may lead to serious injury or drowning. Beach goers
beware, including razor clammers. Never turn your back to the
ocean. -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Monday for PZZ210-251>253-
     271>273.
&&

$$

www.weather.gov/portland

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