Cascade Locks, Oregon Weather Forecast Discussion

228
FXUS66 KPQR 301811
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
1111 AM PDT Tue Sep 30 2025
Updated Aviation discussion & Watches/Warnings/Advisories...
&&
.SYNOPSIS...A fall-like weather pattern is expected to continue
through much of the week as we transition from September into
October. Expect periods of rain through at least Thursday as a
series of fronts 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. Dry weather is expected to return for
the weekend while temperatures remain seasonably cool.
&&
.DISCUSSION...Today through Monday...A more potent frontal
system is expected to push another round of rain onshore
starting this morning through Tuesday night as well as bringing
breezy southerly winds. Current (0230 Tuesday) Water vapor
satellite imagery shows a low pressure system centered near
48N/135W, which looks to have a center pressure around 975-980
mb. Ensemble guidance remains in very good agreement that the
surface low will remain well offshore of CONUS and near
Vancouver Island through at least Friday. By early Friday,
models have this low starting to slowly drop down towards OR/WA
as well as weaken.
Now, onto the series of fronts that this system will be sending
into the Pac NW. The warm front looks to arrive and bring
moderate rain to the area by late Tuesday morning through the
afternoon. Followed by a cold front through the evening and into
Wednesday morning, which will result in more showery rain.
Also, cooler air aloft will also result in elevated instability.
The main chances (15-30%) for thunderstorms remains along the
coast on Tuesday, before spreading inland with around a 15-20%
chance of thunderstorms Wednesday afternoon. Any passing
thunderstorms can bring gusty, erratic winds and heavy rain.
Expect southerly wind gusts along the coast, especially beaches
and headlands, approaching 40-50 mph, with just a 10-20% chance
of high wind gusts exceeding 60 mph as an occluding cold front
approaches the coast. Inland areas will mainly see wind gusts of
30 mph or less. While guidance suggests there is only a 5-25%
chance of wind gusts up to 40 mph, with leaves still on the
trees, there is a small chance for a few broken tree limbs or
garbage cans falling over through Tuesday night. Southerly winds
remain slightly elevated through Wednesday with gusts generally
up to 35 mph along the coast and 25 mph inland.
Total rainfall for the Tuesday 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
the Great Basin from Canada by Friday/Saturday. -42/Hartsock
&&
.AVIATION...Dry conditions with VFR cigs/vis continues across
the region into the early afternoon ahead of an approaching
frontal boundary. As the rain band moves onshore and spreads
from west to east from 20-23z Tue, a degradation to MVFR
cigs/vis is expected 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 shower coverage overnight, increasing 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. These
gusts will develop over the next few hours as precipitation
begins, and then persist through much of the period.
KPDX AND APPROACHES...VFR conditions continue through 21-23z Tue
ahead of precipitation onset, with cigs likely to remain at low-
end VFR levels around 4 kft after rain begins. MVFR cigs at 2-3
kft remain possible, about 20-30% chance. Southeasterly flow
will turn southerly as rain begins, building to 10-15 kt with
gusts to 20-25 kt for much of the period, then easing slightly
late in the period, after 06-09z Wed. -Picard
&&
.MARINE...As a surface low deepens west of Vancouver Island
over through Tuesday another, more potent frontal boundary
approaches the coast. This will result in southerly winds
increase through Tuesday. Current guidance is showing peak winds
up to 45 kt across all waters starting early Tuesday morning
through Tuesday night. Isolated storm-force gusts of 48 kt or
more cannot be ruled out. Seas will also build quickly towards
15-19 ft by Tuesday afternoon, although chances for 20 ft or
greater seas have fallen to less than 5%. While winds are
expected to fall below gale-force by Tuesday night, seas will
remain elevated through Wednesday around 14-18 ft and will
continue to slowly subside towards 10-12 ft by Thursday
afternoon. As a result a Gale Warning will come online for the
outer waters by 5am Tuesday and 11am for the inner waters and
the Columbia River Bar, which will continue through late Tuesday
night. Have also upgraded the Hazardous Seas Watches to
Warnings as elevated seas will persist through at least early
Thursday morning.
Behind the Tuesday/Wednesday front, winds are expected to
steadily weaken below 20 kt by Wednesday night and 15 kt by
Thursday evening. Seas expected to subside towards 6-8 ft by early
Friday morning. As the deep low fills and moves inland by this
weekend, it will likely be replaced by building surface high
pressure over the northeastern Pacific which will see winds
return to seasonable northerly flow. -42/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