025
FXUS66 KPQR 131817 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1117 AM PDT Wed Aug 13 2025

.UPDATE...Dense fog along the coast and over the waters has
begun to dissipate and visibility has improved. Some areas of
locally dense fog remain, especially around the Columbia River
Bar. However, no longer widespread enough to maintain the Dense
Fog Advisory.


&&

.SYNOPSIS...Marine stratus and fog may reduce visibility along
the coast this morning. Today and Thursday will see a relative
cool down as high pressure breaks down and onshore flow
increases. A low pressure system in the northeast Pacific will
bring widespread rain by the end of the week with cooler
temperatures across the region. Drier conditions return heading
into early next week.

&&

.SHORT TERM...Now through Thursday Night...A relative cool down
begins today as high pressure breaks down due to an upper-level
trough descending from western Canada. This will strengthen
onshore flow, shifting winds more west-northwesterly and
bringing a deeper marine layer to the coast. A Dense Fog
Advisory remains in effect along the coast through 11 AM this
morning. Fog and low stratus will be patchy along the north
Oregon and south Washington coasts, but if it does form, it will
be dense. The highest concentration of dense fog will be from
Lincoln City southward towards Florence. Areas from Cannon Beach
north will see fog burn off the quickest in the morning.
Visibility should improve above one quarter of a mile by late
morning (10-11 AM), but marine clouds will be persist throughout
the day.

Onshore flow doesn`t appear to be strong enough to filter
marine stratus into the Willamette Valley, so expect mostly
sunny skies today inland. Afternoon highs are forecast about 10
to 15 degrees cooler than yesterday - mid to upper 80s across
interior valleys. The most noticeable cooldown will be felt the
further north you go. HeatRisk will decrease to a "Minor" level
throughout the region, and overnight lows will become more
comfortable, generally in the upper 50s to low 60s.

By Thursday, the initial trough will continue its eastward
movement, while a new upper-level trough originating from the
Gulf of Alaska begins moving into the Pacific Northwest. This
will maintain strong onshore flow with winds turning more
westerly. Afternoon highs on Thursday are forecast near or
slightly below seasonal averages, reaching the upper 70s to
low 80s inland and the 60s along the coast. Most locations
remain dry on Thursday, however rain chances return Thursday
evening. The north Oregon and south Washington coasts may end
the calendar day with 0.10-0.20" (20-30% chance of exceeding
0.20"), with the highest totals north of Astoria.    -Alviz


.LONG TERM...Friday through Tuesday...Rain chances increase
early Friday into Saturday as the upper level trough from the
Gulf of Alaska continues to progress southward, centering just
offshore of British Columbia. The surface warm front associated
with this system will bring rain on Friday with the trailing
cold front pushing through Friday night into Saturday morning.
This frontal passage will shift winds more southerly to
southwesterly, and last through Saturday. Temperatures Friday
and Saturday will also cool below-normal, with afternoon highs
forecast in the mid to upper 70s across interior valleys.

While there is high confidence that we`ll see widespread
measurable rain across the region, there is still some
uncertainty with exactly how much rain we will receive by the
end of this system. Chances for 0.50" of rain or greater from 5
AM Friday to 5 AM Sunday are around 70-90% from Lincoln City
and Salem northward, and 40-60% south of Lincoln City and Salem
as you head towards Lane County. However, there is still about
a difference of 0.60-0.80" between the 25th and 75th percentile
48-hour QPF across northwest Oregon and southwest Washington.
It will all depend on how far south the trough drops down as
well as the magnitude.

While this kind of pattern is not the most favorable for
thunderstorms, it can`t be completely ruled out. Once the cold
front pushes through on Saturday, will see lingering showers and
potential for some cloud breaks. This could increase afternoon
instability and thus, lead to thunderstorm development. However,
confidence in thunderstorms is low at this time and remain
around a 15-20% chance across the Cascades Saturday afternoon.
Sunday to Tuesday, the trough will weaken and return drier and
warmer temperatures. However, broad troughing remains in place
during this time, maintaining onshore flow.       -Alviz

&&

.AVIATION...Scattered clouds through the next several hours along
the coast with a tendency to lean IFR. Some patchy fog lingers
around KAST and nearby approaches, but not necessarily widespread.
Have included a TEMPO as it appears to be ebbing and flowing in
and out of the terminal. Inland areas will be VFR with generally
clear skies. Towards the end of the forecast, a cold front will
near the coastline with a stratus shield spreading inland ahead
of it. Skies will become overcast after 12Z Thur hovering just
above MVFR category inland.

PDX AND APPROACHES...VFR conditions with mostly clear skies today.
Increasing low clouds tonight, with a 20-30% chance of MVFR CIGs
after 12Z Thur. Northwesterly flow. In the afternoon, westerly
winds will increase closer to KTTD which may impact approaches.
-Muessle

&&

.MARINE...High pressure will maintain northwesterly winds
across the waters through tonight with gusts around 10-15 kt or
less. Seas around 7-9 ft at 8-9 seconds today will gradually
fall to 5-6 ft at 7-8 seconds tonight. Given the choppy seas,
the Small Craft Advisory remains in effect through 1400
Wednesday.

Thursday begins a pattern change as a low pressure system in the
northeast Pacific shifts winds more southwesterly. The latest NBM
guidance projects a 50-70% chance for Small Craft conditions
during the frontal passage on Friday, with the highest chances
across the inner waters north of Cape Foulweather and Columbia
River Bar. Winds weaken heading into the weekend but there is some
uncertainty with the direction. Some models like the ECMWF/Canadian
want to keep low pressure in the northeast Pacific and maintain
southerly winds, while the GFS suggests surface high pressure re-
building over the waters and returning northerly winds.  -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 2 PM PDT this afternoon for
     PZZ271>273.
&&

$$

www.weather.gov/portland

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