840
FXUS66 KPQR 081814 AAB
AFDPQR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
1114 AM PDT Wed Oct 8 2025

Updated Aviation discussion

.SYNOPSIS...Cooler and cloudier weather returns today and
continues through early next week. Low pressure system offshore
will bring persistent chances for rainfall beginning as early
as tonight for the coast and Cascades with chances increasing
late Friday through the weekend as the system moves inland.

&&

.DISCUSSION...Wednesday through Tuesday...There has been very
little change to the forecast since the last forecast package.
Satellite imagery early Wednesday morning shows marine stratus
has returned to the coast due to the return of onshore flow
behind the frontal passage. This stratus will likely push east
into portions of the interior lowlands through Coast Range gaps
through the morning hours as the front continues moving through
western Washington and Oregon. It will dissipate along the coast
by the early morning hours and inland by the afternoon.

An upper level trough deepens off of the West Coast today,
pinching off to form a closed upper low atop a deepening
surface low centered west of the central Oregon coast by
Thursday morning. Due to this, chances for rainfall will
increase through the remainder of the workweek. There remains
some uncertainty in the position of these vertically- stacked
lows, which will affect when rainfall may begin across the
region. At this time, there is a 30-40% chance rainfall may
begin as early as Wednesday night along the coast and a 50-70%
chance across the western slopes of the Cascades. Additionally,
there`s a 30-50% chance for inland valley locales to see rain
by Thursday evening, although these chances are sensitive to the
position of the low. There is high confidence, 70-90% chances,
in rainfall across the region by Friday afternoon and continuing
through much of Sunday as consensus remains high that the broad
area of low pressure will move inland and overhead through the
weekend.

For the period from 5 AM Friday through 5 AM Monday, a
reasonable low-end rainfall accumulation, or the rainfall
amount with a 75% chance of exceedance, is 0.55-0.75" along the
I-5 corridor, and 0.75-1.5" along the coast and in the higher
terrain of the Coast Range and Cascades. Conversely, the
reasonable high-end accumulation (25% probability of exceedance)
is 1.3-1.75" along the I-5 Corridor and 1.5-3.5" along the
coast and in the higher terrain of the Coast Range and Cascades.
Or in an alternative frame, the chances of exceeding 0.5" and
1" of rainfall in the 72-hour period are, respectively, 80-90%
and 45-60% along the I-5 corridor, and 90-100% and 75-90% along
the coast and in the higher terrain of the Coast Range and
Cascades.

Ensemble guidance indicates upper level troughing will continue
across the region Monday. Shower chances continue, though
decrease during the day, with highest chances (60-80%) over the
Cascades. By Tuesday, significant uncertainty returns to
ensemble guidance on the location of the upper level low. About
a 15-40% chance of showers continue through Tuesday, again with
highest chances over the Cascades.

Temperatures will continue to trend cooler across the region
into the weekend, with the snow level falling to 4500-5000 ft
by Sunday morning and remaining low through Monday. This will
allow snow to accumulate in the High Cascades, though only
light and minimally- impactful accumulations are expected at
pass level at this time through Monday. Frost Advisories may
need to be issued in the Upper Hood River Valley as well as
valleys within the Cascades and Coast Range as overnight lows
are expected to fall into the 30s through the weekend.
Elsewhere, temperatures will remain cool with daytime highs in
the 50s and 60s and overnight lows in the 40s. -36/03

&&

.AVIATION...Increasing southwest flow aloft as an upper level
trough drops south just offshore. Lower stratus producing MVFR
conditions across the southern Willamette Valley this morning
expected to lift by 20Z this afternoon. Elsewhere VFR conditions
expected to persist through the period. Showers are likely to
develop over the Cascades later this evening after 06z Thursday,
with lower chances of rain, generally less than 40%, spreading
into the Willamette Valley as well as at the coast. Northwest
winds less than 10 kts across the area will persist through this
evening, becoming ESE after 08z Thu.

KPDX AND APPROACHES...VFR conditions with scattered to broken
mid-level clouds expected through the period. There is a 30-40%
chance of rain showers between 06-12z Thu. Northwest winds around
5 kt expected through this evening. /02

&&

.MARINE...Buoy reports this morning are showing wave heights of
around 7 to 9 ft with a period of 7-9 seconds. Guidance suggests
these seas are likely to continue into early afternoon. Therefore,
have issued a Small Craft Advisory for all coastal waters through
2 PM PDT for steep and choppy seas. Northerly winds will continue
to ease today, falling to 10 kt or less this afternoon.

An area of weak low pressure will approach the coastal waters
from the north today. Northerly winds become variable overnight
as the surface low continues to drop south. The surface low
becomes more organized off the southern Oregon coast on Thursday
as winds turn more offshore Thursday into Friday. Winds expected
to remain less than 20 kts. Seas are likely to linger around 5 to
7 ft through the end of the week. Still some uncertainty where
the surface low ends up by Friday, but will likely push inland by
Saturday with winds becoming northwesterly and breezy. Another
weak low pressure system approaches the coastal waters from the
north late Sunday. /02

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 4 PM this afternoon to 8 PM PDT this
     evening for PZZ210.

     Small Craft Advisory until 2 PM PDT this afternoon for
     PZZ251>253-271>273.
&&

$$

www.weather.gov/portland

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