Orenco, Oregon Weather Forecast Discussion

640
FXUS66 KPQR 201639
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
937 AM PDT Sat Sep 20 2025
.SYNOPSIS...A Fall-like front will bring a quick shot of rain to the
region on Sunday before drier and milder weather return early next
week and persist through at least the middle of next week.
&&
.DISCUSSION...Now through Thursday...As of 4 AM, stratus remains
confined to the immediate coast and coastal gaps, with little
inland penetration so far. Some additional push remains possible
before sunrise, but most inland areas should stay clear. High
pressure will keep conditions calm through today, with highs
reaching the low 80s inland and 60s along the coast. North to
northwest onshore flow continues today, veering westerly and
eventually southwest later in the afternoon as the approaching
front nears. Increasing mid and high clouds will spread inland
during the evening hours ahead of the system.
A stronger shortwave trough moving out of the Gulf of Alaska
will drive a cold front through the region tonight into Sunday.
Current timing brings the front to the coast around midnight,
pushing into the Willamette Valley by roughly 5 AM. Confidence
in precise timing remains modest, but most guidance favors the
system exiting east of the area by around 5 PM Sunday.
Rainfall totals are expected to the highest along the coast,
where 0.50 to 0.75 inches appear likely, with maximum values
north of Tillamook. Inland amounts should range from 0.10 to
0.40 inches, with highest totals northeast of Aurora and into
the eastern parts of the Portland/Vancouver metro. Clusters
indicate a 30 to 60% chance of wetting rain (CWR) across the
area Sunday, rapidly decreasing by the evening. Instability is
limited, but there remains a 5-10% chance of thunderstorms,
mainly near the coast or coastal mountains during frontal
passage.
Sunday will be noticeably cooler with highs in the 60s at the
coast and low 70s inland. After frontal passage, conditions dry
out quickly with a return to more seasonable weather early next
week. Inland highs will rebound to the upper 70s by Monday, with
about a 40-60% chance of reaching 85 degrees on Tuesday.
Forecast confidence degrades midweek. Cluster analysis shows
only 20% of members supporting measurable precipitation by
Wednesday, while Friday carries a roughly 50/50 split between
wet and dry outcomes. Tuesday will also need monitoring for
possible fire weather concerns. While most recent guidance has
trended away from a dry and windy pattern, a minority of
solutions still show humidity values near 25% with sustained
winds around 15 kt along the Cascades and foothills. Overall
confidence in this setup is low, but it remains worth watching.
~Hall
&&
.AVIATION...High pressure aloft will give way to increasing
onshore flow ahead of an incoming cold front that arrives late
tonight. This will maintain coastal stratus along most of the
coast with predominantly MVFR and IFR conditions persisting into
Sunday. Farther inland, conditions will remain predominantly VFR
through 12z Sunday before conditions deteriorate into MVFR
thresholds between 12-18z Sunday as a band of rain tied to the
front pushes into the Pacific Northwest. It should be noted that
there is a 20% chance at any given hour that conditions drop down
into IFR thresholds between 13-18z Sunday. The front will be moving
from northwest to southeast so the window for IFR conditions will
be on the early side of that time window for the Portland TAF
sites and later in that time window for KSLE and particularly
KEUG.
KPDX AND APPROACHES...High pressure over the region will maintain
VFR conditions through 12z Sunday. A cold front and attendant band
of rain will spread over the site Sunday morning. This will bring
a high probability (80-90% chance) of MVFR ceilings spreading over
the site between 12-18z Sunday. Conditions appear likely to
deteriorate rapidly with the arrival of the rain. As a result
there is a 20% chance at any give hour between 13-17z Sunday of
conditions dropping into IFR thresholds.
&&
.MARINE...Seas are currently 5 to 7 ft at 9-10 seconds and
should continue to remain at that level through this evening. A
frontal system arrives tonight from the northwest with winds
turning southerly across the coastal waters beginning this
afternoon. There is an 80%+ chance that winds increase into Small
Craft Advisory thresholds with gusts of 25 kt Saturday night
across the coastal waters north of Cape Lookout. The strongest
winds appear most likely to occur within 10 NM of the north Oregon
and south Washington coast as a weak coastal jet develops. There
is an 80% chance that seas climb into the 7-11 ft range by the end
of Sunday night as a fresh westerly swell moves into the water.
High pressure then returns to the northeast Pacific. This will
result in northerly winds developing across the waters late
Monday into Tuesday. A weak front approaches the region from the
northwest midweek, but appears to stall and dissipate well
offshore so few to no impacts are anticipated.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 11 PM this evening to 7 AM PDT Sunday
     for PZZ210.
Small Craft Advisory from 10 PM this evening to 7 AM PDT Sunday
     for PZZ251-252.
Small Craft Advisory from 8 PM this evening to 6 AM PDT Sunday
     for PZZ271.
&&
$$
www.weather.gov/portland
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NWS PQR Office Area Forecast Discussion