Dee, Oregon Weather Forecast Discussion

621
FXUS66 KPQR 240432 AAA
AFDPQR
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
932 PM PDT Tue Sep 23 2025
Updated aviation discussion.
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.SYNOPSIS...High pressure will maintain warm and dry conditions
across the Pacific Northwest through midweek. A thermal trough
remains in place, supporting offshore flow and continues low
relative humidity, particularly across the Cascades and interior
valleys. Conditions moderate Thursday as onshore flow returns,
bringing slightly cooler temperatures and higher humidity.
Another warming trend is expected over the weekend ahead of an
approaching frontal system, which looks increasingly likely to
bring rain to the region Sunday into Monday.
&&
.SHORT TERM...Now through Thursday Night...Tranquil weather
continues across northwest Oregon and southwest Washington as a
strong upper-level ridge dominates the region. The ridge has
been amplified in part by surrounding upper-level troughs over
the Gulf of Alaska, the Rockies, and southern California. This
pattern has reinforced the warm, dry airmass in place across the
Pacific Northwest.
Offshore flow persists, with the thermal trough extending across
western Oregon. While pressure gradients supported stronger
winds earlier this morning and afternoon, they have largely
diminished as of 3 PM. The key feature through Wednesday will
instead be the very dry air. Afternoon relative humidity values
will remain low, around 30% or less in many areas east of the
Coast Range, mostly notably the southern Willamette Valley and
the Cascades. These dry conditions, combined with above- normal
temperatures, will continue through Wednesday.
Highs both today and Wednesday will generally reach the low to
mid 80s across interior valleys, while the coast holds in the
upper 60s to low 70s. Nights remain seasonable, with lows in the
upper 40s along the coast and low to mid 50s inland. Early
Thursday, the ridge begins to flatten and the thermal rough
weakens, allowing onshore flow to gradually reestablish itself.
While conditions remain dry, the introduction of cooler marine
air will lower temperatures a few degrees compared to midweek.
.LONG TERM...Friday through Monday...Zonal flow aloft will be
the dominant feature Friday into early Saturday, leaving
conditions relatively unchanged to close out the work week
Saturday will act as a transitions period as a longwave trough
approaches the coast, beginning to shift temperature slightly
cooler. Ensemble spread highlights the uncertainty in exact
values, but generally supports highs in the upper 60s to upper
70s across higher terrain and valleys, with interior valleys
holding in the low to mid 80s. Attention then turns to a frontal
system associated with the deepening trough. Recent model runs
have trended toward slower timing, with each successive cycle
pushing precipitation onset later. The latest guidance suggests
light rain could begin at Astoria as early as Saturday, though
for most of the area, rain is not expected until Sunday, with
the bulk of precipitation arriving Monday. Probabilities for
measurable rain range from 40-50% across much of northwest
Oregon and southwest Washington, with chances somewhat lower
farther south. Associated chances of wetting rain (0.25 in or
greater) run around 20-40%, with the lowest likelihood in the
southern Willamette Valley and Lane/Linn County foothills and
Cascades. Confidence in the timing has increased somewhat but
is still best described as low to moderate, with ensemble
clusters converging on the Sunday-Monday timeframe as we move
further into the week.
Overall, this system looks to bring a noticeable cool-down, with
highs returning to near or slightly below seasonal averages by
early next week. Moisture associated with the front will also
provide a welcome break from the extended stretch of dry
weather.
~Hall
&&
.AVIATION...High pressure will maintain VFR conditions for most of
the area. Winds through the Columbia River Gorge and east-west
oriented Cascade gaps remain easterly tonight and into Wednesday
but will gradually shift onshore late Wednesday. Winds less than
10 kts expected through the period. Winds along the coast and
throughout the Willamette Valley north to northwesterly around 5
kt overnight. Winds increase Wednesday with sustained winds 10-15
kt and gusts around 20 kt possible along the coast. Inland, winds
5-10 kt expected. Guidance suggest a low (10-20%) chance for
patchy fog or low stratus to develop along the coast overnight.
KPDX AND APPROACHES...Light northwesterly winds 5 kt or less
tonight, increasing to around 7-9 kt Wednesday. -Batz
&&
.MARINE...Surface high pressure offshore will continue to yield
northerly flow into the weekend. A tightening coastal pressure
gradient will see winds increase to 15-25 kt across the outer
waters tonight, and across the inner waters by Wednesday
afternoon, while seas of 6-9 ft build to 7-10 ft as winds
strengthen. Small Craft Advisories therefore remain in effect
beyond 10 NM, and will go into effect at 11 AM PDT Wednesday
closer to shore, continuing through early Thursday morning.
Conditions will ease Thursday and Friday before building again
ahead of an approaching frontal system this weekend. -Picard
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 11 AM Wednesday to 5 AM PDT Thursday
     for PZZ251>253.
     Small Craft Advisory until 5 AM PDT Thursday for PZZ271>273.
&&
$$
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NWS PQR Office Area Forecast Discussion