700
FXUS66 KPQR 171629
AFDPQR

Area Forecast Discussion...Updated Aviation
National Weather Service Portland OR
929 AM PDT Thu Jul 17 2025

.SYNOPSIS...Onshore flow gradually increases in the coming days
allowing inland high temperatures to decline moving into the
weekend. That said, temperatures likely remain above normal
through Friday for much of the region. Our focus then turns to
the potential further amplification of an upper trough on Monday
as temperatures bottom out, and depending on the track light
precipitation will be in play across the area as well. Low to
moderate forecast confidence Tuesday onward due to rapidly
increasing model uncertainty.

&&

.SHORT TERM...Now through Sunday...After yesterday`s hot
temperatures and broad offshore/easterly flow, expect a switch
back to light onshore westerly flow today into the weekend
allowing conditions to gradually trend cooler the next few
days. Currently, satellite imagery depicts fog and low stratus
firmly in place across the coast into the coast range valleys, a
sign of moister/cooler oceanic air attempting to surge inland.
While models like the HREF show this cloud layer struggling to
penetrate into the Portland/Vancouver metro southward through
the Willamette Valley, this shift in low level flow will be
enough to knock inland high temperatures down into the upper 80s
to low 90s - a noticeable decrease from yesterday (Wednesday).
Highs at the coast hold in the upper 50s to 60s. As a nice added
bonus, the westerly flow should help to keep regional wildfire
smoke confined east of the Cascades, a trend likely to persist
through the weekend as well. Anticipate comparable temperatures
on Friday to that of Thursday although a weak upper-level
trough begins to dig into the Pacific Northwest during the
afternoon hours which at the very least leads to increasing west
winds through the central Columbia River Gorge.

Come Saturday and Sunday both ensemble and deterministic
guidance support broad northwesterly flow as a weak upper-level
troughing is maintained overhead helping to reinforce cooler
conditions and increase morning cloud cover potential - both
along the coast and inland. As the marine layer deepens, there
is growing support for morning drizzle, particularly along the
coast into the west slopes of the coast range. The best window
for this looks to be during the Saturday night into Sunday
morning time period, although it can`t be ruled out Friday night
into Saturday morning. The south Washington and north Oregon
coasts currently carry the highest relative chance (10-20%) of
seeing a few hundredths of an inch, with lower probabilities
south of Lincoln City/Newport. High temperatures over the
weekend likely hold in the upper 70s to low 80s across the
inland valleys, that said, the exact timing of clearing morning
cloud cover will modulate these values. If clearing of the
morning marine stratus deck is delayed by a few hours, which is
sometimes the case (models typically mix out morning clouds too
quickly), these values will trend moreso towards the mid to
upper 70s - something to keep in mind. -Schuldt

.LONG TERM...Monday through Thursday...Looking into early next
week, uncertainty rapidly increases regarding the exact
placement of future trough amplification over western CONUS and
thus chances for light showers/rainfall locally. Ensemble
systems and their respective deterministic counterparts are
struggling to resolve the progression of an upper-level
shortwave running north to south along western B.C. into the
Pacific Northwest slated to arrive on Monday. Exploring the 00z
ensemble space through cluster analysis shows around 45% of the
total ensemble members, and the deterministic ECMWF, depict a
shortwave track and eventual amplification far enough west for
decent light shower chances across the CWA while the remaining
55% keep it shunted further east leading to a drier solution. In
either case, temperatures likely remain a few degrees below
normal on Monday. Would like to see another model run or two
depicting similar probabilities of the former solution before
increasing PoPs on Monday. From there model solutions diverge
further with the ECMWF/Canadian favoring continued troughing
overhead through Wednesday while the GFS tries to slowly
increase upper-level heights. The NBM does favors a gradual
warming trend Tuesday into Wednesday, however, due to the
aforementioned model uncertain forecast confidence out at day
5-7 is only low to moderate at this time.  -Schuldt

&&

.AVIATION...Marine stratus still affecting coastal terminals, with
an MVFR overcast deck around 1500 ft AGL affecting coastal
terminals as of 1630z Thu. Coastal conditions persist through at
least 20z Thu, with some clearing at the northern coast (KAST,
KTMK). Further south (KONP), there is a 50-60% chance of MVFR
conditions persisting throughout the TAF period.

Inland, clear sky VFR conditions throughout the period are
expected. Generally west-northwest winds throughout the period,
with sustained winds around 5-8 kts throughout the period.

PDX AND APPROACHES...VFR conditions throughout the period, with
more or less clear skies. West northwest winds around 5-8 kts
throughout the period. /JLiu

&&

.MARINE...Based on satellite imagery and surface observations, a
Dense Fog Advisory has been issued across all waters including the
Columbia River Bar for dense fog reducing visibility to 1 NM or
less. Conditions should improve by 1200-1400 Thursday as daytime
heating and atmospheric mixing progresses.

A weak surface trough will bring light southerly winds across the
waters today, mainly north of Cape Foulweather. By this evening,
high pressure will re-build and return northerly to northwesterly
winds through next week. The Small Craft Advisory for choppy seas
over the outer waters (10-60 NM out) is set to expire at 0500
Thursday. Winds weaken and seas subside further heading into the
weekend with minimal impacts expected.      -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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