Oswego, Oregon Weather Forecast Discussion

485
FXUS66 KPQR 302100
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
200 PM PDT Tue Sep 30 2025
.SYNOPSIS...A fall-like weather pattern is expected to continue
through much of the week as we transition into October. Expect
periods of rain through at least Thursday as a low pressure system
brings cooler and unsettled weather across the region. Breezy
southerly winds are expected today, followed by rain showers and
chances for thunderstorms as a low pressure system remains offshore.
Any thunderstorm that does develop will bring potential for small
hail, gusty winds, and funnel clouds. Dry weather is expected to
return for the weekend while temperatures remain seasonably cool,
before warming back into the 70s by early next week.
&&
.DISCUSSION...Tonight through Monday...Sunny skies will give way to
increasing clouds and steady rain later this afternoon as a potent
frontal system moves onshore and lifts across the Pacific Northwest.
Satellite imagery shows the associated 972 mb low spinning offshore,
west of Vancouver Island this afternoon. This low pressure system
will then gradually weaken as it meanders toward the WA/OR coast
through Friday.
The initial frontal band will bring a period of steady rainfall,
potentially moderate to heavy at times, as it lifts across NW Oregon
into SW Washington this afternoon. Breezy southerly winds are also
likely with this frontal passage, strongest along the coast,
especially beaches and headlands where wind gusts up to 40-50 mph
will be likely through this evening. Inland areas will mainly see
wind gusts up to 35 mph or less. There remains a very low 5-10%
chance of wind gusts exceeding 45 mph within the Willamette Valley.
With leaves still on the trees, there is a small chance for a few
broken tree limbs.
Behind the front, expect precipitation to become more showery,
continuing through at least Thursday. The cooler air aloft will also
result in elevated instability, with chances for thunderstorms (15-
25%) along the coast today, spreading inland on Wednesday. Any
passing thunderstorm can bring gusty winds, heavy rain, and small
hail. Based on local guidance, this weather pattern also sets up the
potential for funnel clouds as well as water spouts near the coast.
Total rainfall amounts through Thursday are expected to vary
significantly across the area as the rain transitions from
stratiform to showers. This makes it difficult to pinpoint
precipitation amounts at a specific location, but the probabilistic
guidance does provide reasonable low-end to high-end amounts that
will be possible through Thursday. Coastal locations could see
anywhere from 0.50 inch (10th percentile) to 2.50-3.50 inches (90th
percentile); while the inland lowlands are more likely to see a
range between 0.20 to 1.80 in, with highest amounts more likely to
the north. That said in a different way: total rainfall for today
through Thursday is likely (65-85% chance) to exceed 0.5" for valley
locales, with higher chances to the north. Chances to exceed 1" of
rain are the highest along the coast (80-95% chance), in the OR
Coast Range & Willapa Hills (75-90% chance), and in the Cascade
foothills (55-75% chance), and much lower (20-40% chance) within the
Willamette Valley.
By Friday, most ensemble members are showing drier weather returning
through the weekend. WPC 500 mb cluster analysis shows relatively
good agreement of the upper low dropping into northern California to
the Great Basin Friday to Saturday. Northwest flow likely to persist
into early weekend with temperatures seasonably cool. There is also
fairly good agreement of an upper level trough dropping out of
Canada on Sunday, bringing more north to northeast flow later Sunday
into Monday with dry conditions and temperatures likely warming back
into the 70s.  /Hartsock
&&
.AVIATION...Dry conditions with VFR cigs/vis continues across the
region this afternoon ahead of an approaching frontal boundary.
The rain band will move onshore by 00z Wed and continue to spread
from west to east into tonight, producing MVFR vis/cigs along the
coast with continued low-end VFR more likely and only a 20-30%
chance of MVFR cigs inland. Beneath the deep upper low offshore,
isolated thunderstorms are probable enough to merit a PROB30
mention of TSRA with IFR cigs/vis at coastal terminals from 00-09z
Wed. Rain will transition to a more showery distribution after
06-09z Wed, with a minimum in coverage overnight, increasing
again into the day on Wednesday.
Impactful gusty winds are expected across the region. Generally
southerly flow of 10-15 kt gusting to 20-30 kt is expected
inland, and 15-25 kt gusting to 30-40 kt along the coast. The
strongest gusts are expected through tonight, before easing
somewhat while remaining breezy through Wednesday afternoon.
KPDX AND APPROACHES...Cigs/vis likely to remain at low-end VFR
levels around 4 kft during rainfall. MVFR cigs at 2-3 kft remain
possible, about 20-30% chance. Southerly winds of 10-15 kt with
gusts to 20-25 kt are expected into tonight, before easing but
remaining breezy after 06-09z Wed. -Picard
&&
.MARINE...An unseasonably deep surface low west of Vancouver
Island is supporting strong and gusty southerly winds as a potent
frontal boundary moves onshore this afternoon and evening. Winds
are rapidly ramping up to gale-force, with widespread gusts of
40-45 kt very likely. Isolated storm-force gusts in excess of 48
kt are also likely, but are expected to be isolated in coverage
and intermittent. Winds will ease below gale-force this evening
through tonight, with Gale Warnings remaining in effect through 11
PM this evening across the outer waters, and through 2 AM early
Wednesday morning across the inner waters and Columbia River Bar.
Latest guidance also favors a second period of elevated winds
from late Wednesday morning through late Wednesday evening,
particularly north of Cape Falcon and across all inner waters from
Cape Shoalwater to Florence including the Columbia River Bar;
additional Gale Warnings may be issued for these areas tonight.
Afternoon and evening thunderstorms will pose an additional
threat today and Wednesday. Storms will be capable of producing
severely limited visibility, gusty and erratic winds, lightning,
small hail, and even an isolated water spout in their local area.
As winds increase, seas are rapidly building as well, with
widespread wave heights of 15-19 ft expected through tonight
across the waters. While winds ease somewhat, seas will remain
elevated through Wednesday and Wednesday night, with Hazardous
Seas Warnings also remaining in effect across all coastal waters
and the Columbia River Bar from tonight through 8 AM Thursday.
Late in the week, the area of low pressure responsible for this
period of active weather will weaken and move inland while high
pressure builds over the northeastern Pacific. Winds will weaken
below 15 kt while seas subside below 10 ft by Thursday evening,
before the more seasonable patterns turns winds out of the north
to northwest at around 10 kt early Saturday morning. -Picard
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Warning until 2 AM PDT Wednesday for PZZ210-251>253.
Hazardous Seas Warning from 2 AM Wednesday to 8 AM PDT Thursday
     for PZZ210-251>253.
Gale Warning until 11 PM PDT this evening for PZZ271>273.
Hazardous Seas Warning from 11 PM this evening to 8 AM PDT
     Thursday for PZZ271>273.
&&
$$
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NWS PQR Office Area Forecast Discussion