327
FXUS66 KPQR 011104
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
404 AM PDT Tue Sep 1 2026

.SYNOPSIS..An unusually strong series of systems, by early
September standards, takes aim at the Pacific Northwest for the
middle of the week. These systems look to bring widespread
rainfall, locally breezy/gusty winds, and a 15-30% chance for
pop-up thunderstorms, with higher chances on Thursday. Conditions
trend slightly drier by late Thursday/Friday and continue into
the weekend. However, cooler than normal temperatures and shower
chances persist.

&&

.SHORT TERM.. Today through Thursday Night...Well, the days
that we have been talking about have arrived. A series of lows,
dropping out of the Gulf of Alaska will bring widespread rain,
cooler temperatures and breezy/gusty southerly winds across the
CWA. Today, the relatively weaker of the two lows will dive
southward towards the OR/CA border. This will bring the first
taste of fall to the CWA as cloud cover will increase, cooler
temperatures will be experienced along with a 20-30% chance for
light showers. Daytime highs will be in the low to mid 70s for
inland valleys, upper 50s to mid 60s for the coast, and mid 50s
to mid 60s for the Cascades. Winds also begin to turn more
southerly, generally remaining relatively light with gusts below
20 mph. An exception will be the Columbia River Gorge and Hood
River Valley, where westerly gap winds Tuesday afternoon appear
prominent with gusts approaching 35 mph.

Wednesday, is shaping up to be far more impactful for the
region. As mentioned above, a second, more robust low will
closely follow the track of the Tuesday system. However, this
system will bring cooler temperatures and a significant amount
of moisture. So, let`s get to the meat of the forecast and
answer the most pressing question: How much rain to expect from
this system? Taking a look at NBM 48 hour total probabilities
(5AM Wed-5AM Fri), there is an 85% or better probability that
total rainfall amounts will be at least 1 inch from the coast to
the crests of the Cascades. Chances for 1.50 inches or more is
50-80% for the coast and our higher terrain features and 10-30%
along the I-5 corridor. As for 2 inches or more there is around
a 40-60% for the coast and our higher terrain features and 5-15%
chance along the I-5 corridor. Daytime highs on Wednesday are
also looking to be in the mid to upper 60s for inland valleys,
mid 50s to mid 60s for the coast, and low 50s to low 60s for
the Cascades. Following the frontal passage, there`ll also be
a 15-30% chance for thunderstorms. Southerly winds are also
expected to increase on Wednesday. Expect gusts approaching 30
mph for inland locations, gusts approaching 40 mph for the
Columbia River Gorge and Hood River Valley and lastly, gusts
along the beaches/headlands of the coast peaking around 55-60
mph.

As Thursday approaches, winds will ease, but cooler daytime
highs and showers remain in the forecast as the upper level low
meanders over western Oregon. Thunderstorm chances will also
continue through Thursday and look to be slightly more favored
when looking at models soundings. While the shear environment
doesn`t look supportive of long lived cells, pop-corn thunderstorms
are very possible. In addition, cold air aloft will also put
into play the potential development of cold core funnel clouds.
Any passing thunderstorms may produce lightning, heavy rain,
erratic winds, and small hail. /42-99

.LONG TERM...Friday through Monday...Chances for showers likely
linger through the start of next week as the upper-level low
weakens and stalls along the coastline. Daytime highs look to be
in the 60s to 70s with ample cloud cover. Late Monday,
shortwave riding looks to bring a return of rather benign
conditions as ensemble model trends are pointing towards a
slight warming and drying trend to the Pac NW. /42

&&

.AVIATION...Through 12Z Wednesday...Current observations as of 04Z
Tuesday show a mixture of VFR/MVFR conditions across the airspace.
As the day progresses expect MVFR conditions to become the dominant
flight category along the coast and low-end VFR/high-end MVFR for
inland locations as a broad, upper level low swings south of the
airspace. MVFR will be favored at inland locations through around
20Z-23Z Tuesday with VFR favored afterwards and through the
remainder of the TAF period. Southerly winds through the TAF
period, with inland locations expecting winds 10 kt or less and
southerly gusts up to 25 kt along the coast starting around
18Z-20Z Tuesday. Additionally, there`s a 15-30% chance of
scattered rain showers along the coast after 23Z Tuesday through
the end of the TAF period.

KPDX AND APPROACHES...Currently VFR conditions. However, as the
day progresses expect a mixture low-end VFR/high-end MVFR to
develop, with MVFR favored through around 20Z Tuesday with VFR
favored afterwards and through the remainder of the TAF period.
Southerly winds through the TAF period, 10 kt or less. /42

&&

.MARINE...A series of robust lows will move across all waters
through Wednesday. These systems will result in southerly winds
continuing to develop through today with winds developing into
gales starting late tonight through at least Wednesday evening.
Winds will build through Wednesday afternoon, with gusts
approaching35 kt by late Tuesday night/early Wednesday morning.
Peak winds, with gusts approaching 45 kt are most likely from 6
AM through 2 PM PDT Wednesday across the majority of the waters,
and from 11 AM through 5 PM PDT Wednesday within 10 NM of the
coast. There is a 20-40% chance of isolated storm-force gusts
within 20 NM of the coast. Seas are expected to build towards
10-14 ft during this period, peaking Wednesday morning with only
up to a 5-10% chance that significant wave heights exceed 15 ft.
Behind this system, there are 10-20% chances for thunderstorms
across the waters on Thursday. Winds expected to fall below 15 kt
by Wednesday night, seas will be slower to subside likely falling
below 10 ft late Thursday/early Friday. /42-36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Gale Warning from 11 PM this evening to 5 PM PDT Wednesday for
     PZZ210-251>253-271>273.

&&

$$

www.weather.gov/portland

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