312
FXUS66 KPQR 040454
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
954 PM PDT Sun Aug 3 2025

.UPDATED AVIATION DISCUSSION.

.SYNOPSIS...General troughing and increasing onshore flow will
bring relatively cooler temperatures Sunday through Thursday
with increasing chances for cloud cover, especially during the
morning hours. Chances for widespread rain increase Wednesday,
however uncertainty remains high regarding exact rain amounts.
Warmer and drier conditions are expected next weekend as high
pressure builds over the region.

&&

.DISCUSSION...Sunday night through Saturday night...Conditions
tonight and tomorrow will be similar to what was observed last
night and thus far today. Expect some cloud cover tonight through
tomorrow morning before cloud cover begins to scatter out in the
afternoon, except late afternoon for southwest WA. The excess cloud
cover will keep temperatures mild with temps in the 60s much of the
day, except low to mid 70s by the late afternoon in response to
increasing breaks of sun. Note the high temperature forecast was
nudged towards the NBM 10th percentile to lower temps, based on
temperature observations thus far today which are running cooler than
the deterministic NBM.

Cloud cover will increase once again Monday night into Tuesday as
onshore flow continues. Cloud cover should mainly be at low to mid
levels of the atmosphere in the morning, with low clouds attempting
to clear out in the afternoon. However, high clouds will be
increasing from west to east simultaneously. This makes for a tricky
high temperature forecast. If high clouds increase quickly and are
thick enough, highs will most likely stay stuck in the 70s across the
lowlands, except 60s at the coast. If high clouds hold off until late
in the day or if high clouds are thin enough, highs in the low to mid
80s are possible for inland valleys.

The aforementioned increase in high clouds Tuesday afternoon/evening
will be in response to an incoming upper level trough and attendant
pair of surface fronts. This system will bring increasing chances for
widespread rain along the coast Tuesday night and for inland areas
Wednesday. NBM PoPs have increased a bit with this system, which
seems reasonable based on QPF ensemble guidance from the
GEFS/GEPS/ENS as only a small handful on members show no rain at all,
except from Salem to Eugene and over the Lane/Linn County
Cascades/foothills where there a more considerable number of ensemble
members showing no rain at all (mainly from the GEFS which continues
to trend drier than the ENS/GEPS). NBM PoPs are lowest in these
areas, which makes sense per ensemble guidance and the northern track
of the trough. NBM 24-hr PoPs now range between 50-80% over southwest
WA, the coast and Portland metro. PoPs are closer to 25-35% from
Salem to Eugene. While confidence remains low regarding exact rain
amounts for locations that do observe rain, there is now more notable
ensemble clustering for amounts below 0.2-0.3 inches and fewer
outliers than are above 0.5 inches. The probability for 0.25 inches
of rain or more ranges between 20-40%, except 40-70% over southwest
WA (highest probabilities are for the Long Beach Peninsula and
Willapa Hills). Hopefully these higher rain amounts come to fruition,
as this amount of rain would be enough to temporarily dampen wildfire
season.

Conditions will begin to dry out from Thursday onward as high
pressure gradually rebuilds over the region. This will also result in
a warming trend with temps warming a few degrees each day, most
likely peaking on Sunday with highs in the 90s for inland valleys.
-TK


&&

.AVIATION...Conditions are generally VFR across this region late
this evening, however, MVFR/IFR ceilings are expected to
redevelop along the coast through the overnight hours becoming
fairly widespread by 10-14z Monday. Additionally, there`s a
40-70% chance of MVFR ceilings redeveloping inland between 10-14z
Monday, lingering through 17-20z Monday. Highest relative
confidence for MVFR CIGs inland at KPDX, KTTD, KUAO, and KEUG.
Back to VFR CIGs Monday afternoon. Winds remain fairly light out
of the north to northwest, mainly less than 10 knots.

PDX AND APPROACHES...VFR conditions currently prevail. However,
there`s a 60-70% chance for MVFR ceilings redeveloping between
12-14z Monday, dissipating by 18-20z Monday. Expect northwesterly
winds under 10 kt through the period. -Schuldt/HEC

&&

.MARINE...Minimal change in the forecast as a persistent
pattern will maintain relatively calm seas. Seas remain 3 to 5
feet through the week and into next weekend. Winds will be
northwesterly 10-15 kt with gusts as high as 20 kt along the
coast and the far outer waters through Monday. Due to the
northerly flow, the inner waters will see the gustier conditions
though will remain just below critical criteria.

On Tuesday, a low pressure system drops south into Haida Gwaii,
bringing southerly winds over the waters. Within the inner waters
there will once again be an increase in winds, but gusts are still
expected to remain 21 kts, Small Craft Advisory levels. However,
wind waves will still react and thus bring combined seas to 4-6
ft at 10-12 seconds.

&&

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

$$

www.weather.gov/portland

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