077
FXUS66 KPQR 271121
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
421 AM PDT Sun Sep 27 2026

.SYNOPSIS..Dry weather persists the next couple of days
accompanied by near to slightly below normal temperatures. A
weakening frontal boundary presents our next opportunity for
light rain on Tuesday into early Wednesday with the best
chances along the coast, Coast Range, and Cascades - mostly dry
inland valleys. From there, ensemble favor dry weather across
the region to end the week.

&&

.DISCUSSION...Now through Saturday...High pressure near the
surface continues to linger overhead as an upper-level trough
of low pressure well off the coast transitions into a closed low
and dives into California. This pattern supports continued calm
conditions across the region albeit with some weak
easterly/offshore flow today, turning a light onshore for
Monday. High temperatures both today and Monday generally rise
into the upper 60s to low 70s across the inland valleys which
ends up falling just a degree or two short of our normal high
temperatures for this time of year. Tonight into Monday morning clear
skies and light winds, especially in sheltered valleys, will
promote efficient cooling which may led to two potential
impacts. The first is for isolated pockets of frost in some of
our high mountain valleys, like the Upper Hood River Valley, as
low temperatures could again fall into the mid to upper 30s.
However, chances for temperatures to drop below 36 degrees are
only around 15-20% come Monday morning. The second impact is
patchy fog potential during the sunrise hours where low-level
moisture, the aforementioned efficient cooling, and light winds
overlap. The central and southern Willamette Valley, Coast
Range valleys, and Cascade valleys are among the more favored
locations for fog. Any fog should be localized and dissipate by
late morning.

The next meaningful change arrives Tuesday as a upper-level
trough and weakening frontal boundary move into the region. The
highest confidence for measurable precipitation remains along
the north Oregon coast and Coast Range into southwest
Washington, where precipitation probabilities now sit around
60-90% during the day Tuesday before decreasing Tuesday night
into Wednesday morning. Some precipitation may extend into the
northern Oregon Cascades as well. Farther inland and lower in
elevation, the signal for rainfall much weaker, with only
around 10-30% of ensemble members indicating more than a trace
of precipitation in the Portland metro and Willamette Valley
Tuesday through Wednesday morning. Thus, inland valley locations
likely end up mostly dry through this midweek period especially
the further south you go.

Dry conditions are expected to return by midday Wednesday
at the latest through Thursday. Ensemble guidance becomes
increasingly spread out late next week but the larger-scale
flow remains fairly progressive overall. Some solutions favor
another weak trough and cooler conditions with a few light rain
chances along the coast on Thursday, while others maintain zonal
flow or weak ridging and generally dry weather. Specifically,
the latest ensemble clusters are as such: 35% weak troughing,
35% weak ridging, and 30% roughly zonal. There is not yet
enough agreement to favor a specific outcome, that said, the
weather related impacts from any of these scenarios appear
rather benign. -99/12


&&

.AVIATION...Through 12Z Monday...Primarily VFR conditions are
expected through the TAF period. Early this morning a scattered
to broken high level cloud deck AOA ~20,000ft continues to move
across portions of the region however the central and southern
Willamette Valley have begun to clear more noticeably while
winds lighten. This may pave the way for patchy fog/low stratus
development again between 12-16z with IFR/LIFR conditions. The
best chances for degraded conditions (30-40%) appear to be at
KEUG and to an extent KONP/KSLE (10-25%) with only a 5-10%
chance elsewhere. Should any fog/low stratus occur it will
quickly clear by 16-17z at the latest. North winds increase
again along the coast to 15-20 kt by 19-21z today, though they
remain generally less than 10 kts inland.

KPDX AND APPROACHES...VFR conditions are anticipated through
the TAF period. Thanks to high clouds overnight into this
morning and northerly winds keeping the atmosphere mixed,
chances for morning fog/low stratus are very low, only ~5%
locally at PDX. North to northwest winds around 5-10 kt through
the period. -99

&&

.MARINE...Expect northerly winds to persist across the coastal
waters today thanks to lingering high pressure near the surface
helping to facilitate gusts up to 20-25 kts at times. There`ll
likely be a short lull in wind gusts this morning, mainly across
the inner waters, before they increase again this afternoon
into the evening. Small Craft Advisories remain in effect through
11 PM PT Sunday. Wave heights will remain around 4-6 ft at 8-10
seconds through tonight.

Then our focus shifts to a frontal boundary approaching the
waters on Monday shifting winds more westerly during the daytime
hours then eventually southerly Monday evening. This frontal
feature finally moves through the waters the second half of
Tuesday. There are high chances (70-90%) of wind gusts exceeding
21 kts(Small Craft Advisory criteria) late Monday into Tuesday
for the coastal waters north of Cape Falcon, with gusts most
likely peaking around 25-30 kts. Lighter northerly winds return
Tuesday night. A longer period west to northwesterly swell of 5-8
ft at 12-16 seconds will also move into the coastal waters late
Monday through Wednesday, resulting in a moderate sneaker wave
threat and increasing significant wave heights into the 6-9ft
range. While seas gradually fall into Thursday, models hint at
the arrival of another WNW swell of similar magnitude around
Friday. -99/03


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     PZZ210.
     Small Craft Advisory from 2 PM this afternoon to 8 PM PDT this
     evening for PZZ210.
     Small Craft Advisory until 11 PM PDT this evening for
     PZZ251>253-271>273.
&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland