Oswego, Oregon Weather Forecast Discussion

739
FXUS66 KPQR 080423
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
923 PM PDT Sun Sep 7 2025
Updated aviation discussion.
.SYNOPSIS...A closed upper level low pressure will bring cooler
and showery weather to the region Monday and Tuesday before the
area gradually dries out late in the week. There is a 60-70%
chance another Fall-like storm system impacts the region next
weekend.
&&
.SHORT TERM...Now through Tuesday Night...Visible satellite
imagery this afternoon reveals morning stratus slowly
dissipating from southwest to northeast across the area.
Suspect most areas except for some spots in the Cascade
foothills and portions of southwest Washington should at least
get a sunset this evening. Convection has been firing over
central Oregon this afternoon, but the southwesterly flow should
generally keep most convection late this afternoon and early
this evening east of the Cascade crest. The main exception to
this will be across far eastern Lane County where any storms
that develop over eastern Douglas County could briefly traverse
the region between Diamond Peak, Willamette Pass, Waldo Lake and
the Three Sisters.
Water vapor satellite imagery reveals a rather impressive
shortwave trough over the eastern Pacific off the coast of
Oregon and California. An embedded area of low pressure is
producing a fairly large of convection. Global ensembles are in
good agreement this system will move towards the Pacific
Northwest over the next 24 hours. While the best dynamics will
slide south of the region, it appears there will be enough
instability and large scale lift to generate considerable number
of showers and isolated embedded thunderstorms across the
southern half of the area Monday morning that will then spread
northeastward across the area through the day. The upper level
trough will be directly over the region on Tuesday, which should
lead a continuation of showers. The weak flow through the
atmospheric column on Tuesday will likely inhibit updrafts from
persisting long enough to generate deep updrafts, though.
The north Oregon Coast Range and southwest Washington will
generally experience lower rainfall totals compared to areas
farther south Monday and Tuesday. The good news is that the
region most in need of rain, eastern Lane and Linn Counties, has
the highest probabilities (70-90% chance) of experiencing
rainfall totals in excess of 0.50" of rain between Monday and
Tuesday.
.LONG TERM...Wednesday through Sunday...Ensembles are in general
agreement the aforementioned closed upper level low pressure
will slowly meander eastward over the northwestern Great Basin
during the middle of next week. As the upper level exits the
region, shortwave ridging will shift across the area and allow
the area to at least temporarily dry out late in the week.
Nonetheless, there are still a subset of ensemble members that
keep the upper level low pressure close enough to the region
that embedded shortwave troughs rotating around the parent low
keep shower chances going Wednesday into Thursday, particularly
across the Cascades.
Global ensembles have shown a marked uptick in the number of
members depicting a scenario where another shortwave trough will
push into the Pacific Northwest next weekend. This would bring
another round of cooler temperatures and wet weather to the
region, which would be good news for further subduing the 2025
fire season. With that said, there are still considerable
differences in details including how the upper level trough will
evolve and timing. NBM PoPs and temperatures all appear
entirely reasonable given the uncertainty in details so the long
term forecast remains unchanged.
&&
Predominately VFR conditions persist through across NW Oregon and SW
Washington. There`s a 40-60% chance for MVFR ceilings to develop
along the coast after 06-08z Mon. Chances for IFR/LIFR conditions
have decreased, though can`t rule out ceilings dropping for a few
hours. Conditions expected to improve again to VFR by 17-19z Mon.
Scattered showers are forecast to move from south to north across
the area after 12-15z Mon. There`s quite a bit of uncertainty in
exact timing of showers, but general thinking is showers will reach
KEUG by 12-15z and KPDX by 18-20z.
Additionally, there`s a 15-25% chance of isolated thunderstorms
developing after 21z Mon. Conditions could temporarily lower to
MVFR/IFR in showers/thunderstorms, and any thunderstorm could
produce heavy rain, gusty winds, frequent lightning, and small hail.
Otherwise, winds generally light and variable.
PDX AND APPROACHES...VFR conditions will persist through the TAF
period. Winds variable less than 6 kts. Rain showers may arrive at
the terminal around 18-20Z Monday with thunderstorm chances after
00z Tue. Brief MVFR/IFR conditions possible in
showers/thunderstorms. -HEC
&&
.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. Seas will increase to around
6 to 7 ft. Probabilities for seas over 10 ft are under 5%. There
are no signs conditions will meet Small Craft Advisory criteria
through the week. Into next weekend, there is a 5-10% chance we
could see gusts up to 21 kt in the outer coastal waters.
~Hall/TK
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$
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NWS PQR Office Area Forecast Discussion