157
FXUS66 KPQR 122237
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
337 PM PDT Fri Sep 12 2025

.SYNOPSIS...A brief warming trend continues through the first
half of the weekend as dry conditions prevail. However, this
break appears short-lived as our next frontal system arrives
Saturday night to Sunday bringing widespread light rainfall to
most areas. Conditions dry and warm up again early next week
with the potential for offshore winds Monday night through
Tuesday.

&&

.SHORT TERM...Now through Sunday Night...Late this afternoon
clearing has finally overtaken the Portland/Vancouver metro down
through the Willamette Valley and into the Cascades as with
temperatures likely topping out in the low to mid 70s where this
clearing is present. The axis of a transitory upper-level ridge
of high pressure is expected to pass overhead tonight favoring
an even shallower marine layer headed into Saturday morning.
Models suggest that low stratus and fog likely re-develops
across the Willamette Valley and southwest Washington lowlands
as the surface moistens under the nighttime inversion, but again
in weaker/thinner state than past nights. This`ll least to quicker
clearing Saturday morning and thus higher temperatures (upper
70s to near 80) Saturday afternoon across the interior valleys.
By Saturday evening, the aforementioned shortwave ridge
progresses eastward with increasing cloud cover across the area
as the next frontal system approaches.

Cooler temperatures and widespread light rainfall is likely
(70-80%) by Sunday morning as a shortwave trough and
accompanying cold-front swing through western Oregon and
southwest Washington. While precipitation along the immediate
frontal boundary may be more stratiform in nature, rainfall
quickly transitions to lingering showers by the midday hours.
Forecast rainfall totals from late Saturday evening through
Sunday evening are projected to be in the 0.10-0.30" range
across most interior valleys, 0.20-0.40" along the coast, and
0.30-0.60" across the Coast Range, Willapa Hills, and Cascades
with the highest relative amounts on the western slopes of these
terrain features. However, confidence in these totals are only
moderate as over the past several model runs guidance has slowly
been trending downward with our storm totals as is often the
case for these early fall systems. That`s not to say large
swaths of the region won`t get any rain at all, but amounts
outside of the west slopes of the coast range appear rather
light. By Sunday evening, the front further weakens and rapidly
exits to the east allowing any lingering shower activity to
taper off overnight into early Monday morning. -Schuldt

.LONG TERM...Monday through Thursday...Shortwave ridging
returns on Monday as will drier conditions and clearing skies
by Monday afternoon. Then come Monday night into Tuesday there
is high agreement among ensemble members in a return to above-
average 500 mb heights as the ridge axis centers over the
Pacific Northwest. This is in addition to a near surface
thermal trough amplifying across western Oregon with higher
pressure east of the Cascades, leading to an offshore flow wind
pattern and a sharp spike in high temperatures. There remains
some uncertainty in the exact placement the thermal trough
feature which would determine the strength and western extent of
offshore winds, but for now they don`t appear particularly
strong. Still, a -3 to -5mb gradient from KTTD to KDLS Tuesday
may yield at least breezy east winds through the Columbia River
Gorge with gusts up to 25-35 mph east of Troutdale. This Monday
night through Tuesday period needs to be monitored in the
coming days given an expected drop in relative humidity compared
to past days. Fortunately, westerly flow returns Tuesday night
into Wednesday morning mitigating any further concerns.

Forecast confidence begins to decrease Wednesday and Thursday as
ensemble systems struggle with the exact progression of the
upper-level pattern. For Wednesday into Wednesday night most
ensemble systems do show a troughing feature moving into far NW
CONUS but there`s a decent spread in the longitudinal placement
and moreso the amplitude of said feature. At least in almost
all scenarios the frontal boundary paired with this trough
appears to deteriorate before reaching our area. There is a
slight chance (20-25%) that we could see some light showers
mainly along the coast and southwest Washington. -Schuldt/Alvis

&&

.AVIATION...Mainly VFR conditions across the area. Marine stratus
has mostly dissipated across the area with only KAST still hanging
on to MVFR CIGs. Winds remain from the north/northwest at 5 to 10
kt and are expected to become light and variable overnight.
Another repeat is expected tonight with stratus moving in along
the coast between 04-06z Sat and between 10-12z Sat inland.
Probabilities for sub- VFR CIGs along the coast are >80% while
inland they are between 40-60%. Expect clouds to clear inland between
18-20z Saturday. Winds increase from the south/southwest Saturday
morning ahead of an approaching cold front.

KPDX AND APPROACHES...VFR conditions through the evening and into
the overnight. Winds from the northwest around 5 kt. Another
round of stratus is expected to move in between 10-12z Sat,
bringing MVFR CIGs, clearing between 18-21z. Winds increase from
the southwest Saturday morning, remaining light around 5 kt. -Batz

&&

.MARINE...High pressure will give way to a low pressure system and
associated cold front approaching the area overnight. Variable
winds expected to become southerly late this evening into early
Saturday morning. Seas 6-8 feet at 10-13 seconds expected through
the weekend as a northwesterly swell moves into the waters. Winds
expected to increase Saturday evening to 10-15 kt with gusts to
around 20 kt through Sunday morning. Hourly wind gust probabilities
for gusts of 21 kt or greater Saturday afternoon through Sunday
afternoon are remain around 10-35%, with the highest chance along
the far outer waters. 24 hour probabilities are 20-50%, again
highest for the far outer waters. Given the low confidence in
persistent gusts of 21 kt or greater, will continue to hold off on
any products.

A small craft advisory is in effect from 6 pm Friday to 1 am
Saturday for the Columbia River Bar. Seas around 7 feet are
expected with a strong ebb current of 5.8 kt which will create
Rough Columbia River Bar conditions, hazardous to small craft.

Next week looks mostly benign. A building ridge of high pressure
is expected to support an area of thermal low pressure that will
increase the pressure gradient over the waters on Tuesday. Could
see some gusts to around 21 kt during the afternoon and evening
hours but to much uncertainty this far out to have high
confidence. -Batz

&&

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

$$

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