314
FXUS66 KPQR 090416 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
916 PM PDT Wed Oct 8 2025

Updated aviation discussion.

.SYNOPSIS...Cooler and cloudier weather continues through early
next week. Low pressure system offshore will bring persistent
chances for rainfall beginning tonight for the coast and
Cascades and for inland locations by Thursday evening.
Precipitation chances will steadily increase through the latter
part of the week and persist through the weekend as the system
moves inland. Also, don`t be surprised if the higher elevations
of the Cascades see some light snow accumulations this weekend.

&&

.DISCUSSION...Tonight through Tuesday...Well, fall like weather
has finally come to the Pac NW. This will bring cool, moist
onshore flow as well as widespread rain across the CWA through
the weekend and likely into the start of next week. Not to
mention that the higher elevations of the Cascades could even
see some very light snow accumulations starting late Saturday
night/early Sunday morning. Now with the overall picture laid
out in front of us, let`s get into the details (science).

The primary synoptic feature that will be the cause of this
fall like weather, is a broad area of low pressure centered
around 49.13N/128.52W that is slowly moving southward. As this
low moves southward, it looks to strengthen/deepen and as it
does this it will send a series of fronts across the Pac NW that
will bring cooler air along with widespread precipitation.
Current models are showing 850 mb temperatures, associated with
this low around 2C to 4C. What this means is that daytime highs
will start off in the upper 50s to mid 60s and slowly cool by
about 2 to 4 degrees F each day, through Sunday, as cooler 850
mb temps slide into the region. Overnight lows, will not be as
variable with most of the region expected to be in the mid 40s
to mid 50s. However, by Saturday night/Sunday morning areas near
Hood River, some of the mid-elevations within the Cascade
Foothills as well as higher elevations of the Cascades could see
overnight lows at or around freezing. 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 and into the
start of next week. So, if you have any sensitive plants
outside, now would be a good time to start thinking about how to
protect them.

Now, let`s talk about precipitation. As this low pushes
southward models are in excellent agreement that widespread
precipitation will impact the region. While there remains some
variability in the timing and overall precipitation amount`s,
we can get an idea of the precipitation spread that the models
are showing.

Late tonight through Tuesday night storm total precipitation:
        The Coast:         1.30"-2.20"
        Coast Range:       1.30"-2.50"
        Willamette Valley: 1.00"-1.50"
        Cascade Foothills: 1.25"-3.00"
        The Cascades:      2.25"-3.75"

Now, these values are subject to change as timing of any
precipitation as well as the overall movement of the low could
change and that could easily impact precipitation totals for any
given location.

As we get towards the end of the weekend and into the start of
next week, the aforementioned low, is expected to make an
easterly move and come onshore around the OR/CA border. As this
happens, much cooler air will start to be introduced into the
Pac NW and will result in rain becoming snow for elevations at
or around pass level (4000-5000 ft). Currently, snow accumulations
look to be very light, with 1-3 inches of total accumulation
spread across 24-48 hours. Overall, minimal impact from this
snow is expected for the High Cascades.

For the start of next week, models are showing a low diving
southward out of western Canada. This low looks to keep cool and
moist conditions in the forecast as well as the potential for
precipitation. While there remains some uncertainty as to the
strength and position of this Canadian low, the WPC 500 mb
clusters all show a broad trough persisting along the W/NW coast
of CONUS. /42

&&

.AVIATION...Expecting VFR conditions across the area through the
TAF period. Clouds across the coast has mostly cleared while
inland clouds remain around 5-7 kft. Winds increasing from the
southwest at the surface and lower levels will help moisten the
atmosphere. This will bring a chance (40-70%) for light rain
across the Cascades. Lower chances around 20% for the Willamette
valley and Coast Range. Cloud cover is expected to break up across
the Willamette Valley overnight, maintaining VFR conditions.
Upper level cloud cover increases Thursday afternoon as an upper
level low drifts closer to the region. Winds remain southerly
around 5-10 kt for the most part, could see winds shift out of the
ESE late tonight through Thursday morning as a surface low
develops off the central Oregon coast.

KPDX AND APPROACHES...Expecting VFR conditions to prevail through
the period. Cloud deck around 5 kft will persist overnight. Low
chance (~20%) for a stray light shower overnight. Increasing mid
and upper level clouds on Thursday. Southerly winds around 5 kts.
-19

&&

.MARINE...Light and variable winds expected through this
evening as an area of weak low pressure develops over the
coastal waters. The surface low becomes more organized off the
southern Oregon coast on Thursday as winds turn more offshore
Thursday into Friday. An initial frontal band is expected to
lift across the coastal waters late tonight into Thursday
morning, which could produce isolated thunderstorms and periods
of breezy southeast winds, with isolated gusts up to 25 kt.
Breezy southerly winds are likely to continue across the outer
coastal waters into Thursday afternoon, and depending on the
strength an location of the low, there is a possibility that
winds reach thresholds for issuing a Small Craft Advisory.
Southeast winds expected to ease somewhat through Thu night.
Seas are expected to linger around 5 to 7 ft through Friday.
Still some uncertainty where the surface low ends up by Friday,
but will likely push inland by Saturday with winds becoming
northwesterly and breezy. An incoming northwest swell will
likely push seas up to around 10 to 12 ft late Saturday into
Sunday. Another weak low pressure system approaches the coastal
waters from the north late Sunday. /02

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

www.weather.gov/portland

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