Durham, Oregon Weather Forecast Discussion

551
FXUS66 KPQR 071056
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
356 AM PDT Sun Sep 7 2025
.SYNOPSIS...A closed upper level low will settle over the area Monday
into Tuesday, bringing cool, cloudy and wet weather as widespread
rain showers move in from the south Monday morning and afternoon.
Remaining cool on Wednesday with showers becoming more limited to the
Cascades. Trending drier Thursday and Friday with slightly warmer
temperatures.
&&
.SHORT TERM...Now through Tuesday night...The short term forecast is
highlighted by fall-like weather with cooler temperatures, cloud
cover and widespread rain showers beginning Monday. Starting off with
today, expect widespread cloud cover to linger through most of the
day, keeping high temperatures in the low to mid 70s. Areas of
drizzle are possible this morning, especially over the Portland
metro. Otherwise expect mainly dry conditions, aside from the
Lane/Linn County Cascades where there is a 20-30% chance of
thunderstorms Sunday afternoon, especially near the Cascade crest.
Conditions will become cooler and wetter on Monday in response to a
closed upper level low currently centered over the northeast Pacific,
which is set to move into western WA/OR early in the week. Timing
information from the HREF ensemble mean suggests rain showers will
move into the area from the south Monday morning and afternoon, most
likely beginning in Lane County between 8-10am before reaching Salem
around 10-11am and the Portland/Vancouver metro by 11am-1pm. It
appears showers hold off for most of southwest WA until 2-5pm.
Confidence is high all locations will see rain showers with this
batch of precipitation, except for the south WA/north OR coast and
Willapa Hills where confidence is lower and rain chances are only
around 50%.
Showers should become less widespread Monday night before becoming
widespread again Tuesday afternoon. Conditions will then attempt
drying out Tuesday night into Wednesday as showers diminish,
especially over the lowlands. Until then, how much rain will fall?
WPC`s latest QPF guidance came down slightly, but still suggests
substantial total rain amounts of 0.3-0.8 inches (covering a 48-hr
period from 5am Monday until 5am Wednesday). Note the higher rain
amounts are forecast in the Cascades and foothills. Probabilities for
48-hr rain amounts of 0.5 inches or more remain high at 60-90%, with
the highest probabilities over the Oregon Cascades and foothills. The
one exception is for the south WA/north OR coast, Willapa Hills, and
lower Columbia where probabilities range from 25-40% for 0.5" or
more. Note locations that see repetitive heavier showers could see
over 1" of rain. -TK
.LONG TERM...Wednesday through Saturday night...Forecast confidence
has increased a bit on Wednesday on Thursday, which has begun
trending drier with lower chances for rain showers as the closed
upper level low centered over the area early in the week drifts
southward into northern California. The latest NBM PoPs reflect this
well, only peaking around 15-30% now, except 40-50% in the Oregon
Cascades. Even if rain does occur west of the Cascades on either or
both days, expect rain amounts to be light as even the wettest
ensemble guidance only shows a few hundredths of an inch or so.
The forecast becomes more uncertain Friday into Saturday as models
begin to diverge on the evolution of the upper level low, mainly in
regards to how fast it will weaken and progress eastward. That being
said, nearly 80% of the total ensemble space from the GEFS/GEPS/EPS
suggest this low will be focused over Nevada late in the week with
weak shortwave ridging pushing into western Oregon. This outcome
would favor dry weather with slightly warmer temperatures, which is
what the deterministic NBM and current forecast reflects. Assuming
this outcome comes to fruition, expect high temperatures in the mid
to upper 70s on Friday and Saturday, or even lower 80s if enough
sunshine occurs. The exception will be at the coast where highs in
the 60s will remain in place each day. -TK
&&
.AVIATION...An expansive marine stratus deck will most likely
remain in place through at least 20-22z Sunday, resulting in
persistent MVFR cigs at all terminals before conditions trend
towards VFR thereafter. Cigs have lowered to 1300 ft at KTTD and
have the potential to fall as low as 900-1000 ft at any time
through 15z Sunday (10% chance). In addition, cigs may
temporarily lower down to 600-800 ft at KAST at any time through
16z Sunday (50% chance). Winds remain light and variable around 5
kt or less at all terminals.
In regards to precipitation, showers and thunderstorms have moved
out of the area into northwest Washington. Meanwhile, areas of
marine layer drizzle will continue over the Portland metro this
morning, impacting KPDX and KTTD at times. Looking ahead, rain
showers will spread from south to north over northwest Oregon
between 12-18z Monday, likely reaching into southwest Washington
around and after 21z Monday.
PDX AND APPROACHES...Expect MVFR cigs to persist through at least
20-22z Sunday before trending to VFR thereafter. Occasional
drizzle will continue at the terminal this morning, lowering
surface visibilities down to 5-6 SM at times. Any lingering
drizzle should come to an end shortly after sunrise. Winds remain
light and variable around 5 kt or less. -TK
&&
.MARINE...Southerly winds will continue over the waters through
Monday as low pressure remains in place over the northeast
Pacific. Winds become light on Tuesday as this low moves overhead.
Seas remain under 5 ft through Tuesday.
Light northerly winds return for Wednesday and Thursday. There is
a 70-90% chance combined seas will climb above 5 ft on Wednesday
and Thursday over the outer waters. Probabilities for seas over 10
ft are under 5%. There are no signs conditions will meet small
craft advisory criteria through the week. -TK
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$
www.weather.gov/portland
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NWS PQR Office Area Forecast Discussion