729
FXUS66 KPQR 290954
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
254 AM PDT Fri Aug 29 2025

.SYNOPSIS...High pressure over the area will keep conditions dry
and warm through the day. An area of low pressure offshore will
skirt the coast with low probability for showers along the coast.
Any rain that does fall will be sparse and minimal as it will
have to combat a deep layer of dry air. High pressure builds
through next week with increasing temperatures each day.


&&

.SHORT TERM...Now through Sunday...The overall pattern has
experienced minimal change as high pressure builds inland, with
a broad low over the northeast Pacific. Temperatures will be
warm with highs in the upper 80s to near 90 deg F with the
southern portions of the forecast area and urban areas running
warmest. A weak thermal trough will form in the afternoon
shifting east through the afternoon. Expecting typical
summertime diurnal winds where they will be westerly to
northwesterly in the afternoon, then weakly easterly overnight
as the trough returns to the coast.

On Saturday and Sunday, the low aloft will advance towards the
coast but not necessarily push inland. Could see more high level
clouds as a cirrus shield moves in but not expecting dense
cloud cover. However, the low will be wrapped in cooler and more
moist air so temperatures will decrease. In previous model
runs, the fluctuation was much great than it currently is -
likely due to the low staying further offshore. 850 mb
temperatures are around 16 deg C which generally equates to
highs in the mid 80s in the valley, mid 70s along the Cascades,
and in the 60s along the coast. This low will remain nearly
stationary through the weekend with minimal change between
Saturday and Sunday.
-Muessle

.LONG TERM...Monday through Thursday...The long term forecast
remains a mixed bag though there is a bit more continuity in the
overall synoptic pattern. 500 mb heights are in decent agreement
with the low in the northeast Pacific clinging onto the
Washington coast through Monday and a secondary tropical low
advecting over California by Tuesday. This low will amplify the
already present ridge causing temperatures to increase every day
by a few degrees. The main days of focus in the long term will
be Wednesday and Thursday. At this point the upper level low
over northern California will push into southeastern Oregon on
Wednesday causing the ridge to build further. Based on
climatology, the temperatures are rising to anomalous levels
and thus could see another multi-day minor heat spell.

On Wednesday, 850 mb deterministic temperatures are around 24
deg C and on Thursday they are around 25 deg C. There continues
to be a large amount of uncertainty in the sensible weather
though. Looking at the ensembles, there is nearly a 20 degree F
spread in high temperatures on Wednesday and Thursday. At the
low end (5% chance) temperatures would be seasonable around 87
deg F. On the high end though (also a 5% chance), highs could be
as hot as 105 deg F. A 20 deg F spread though is way too far to
come to any conclusions on HeatRisk. As it stands, HeatRisk is
"Major" within the Northern Willamette Valley on Wednesday and
Thursday. However, in comparison to yesterday`s forecast,
temperatures on those two days have risen by around 7 deg F.
Therefore, there is ample room for changing conditions in the
long term with incredibly low confidence.

The components of the long term forecast to watch for though is
the location of the persistent northeast Pacific low and one
dipping down into the northern Plains from Canada. There will be
a trough of cooler air stemming from Canada moving over the
Northern Plains on Thursday which, in combination with the ridge
and considerably higher temperatures over the area, could create
a more dynamic pattern. At this point, it is not concerning, but
if the gradient between the two increases we could be looking at
a windier scenario. Not necessarily seeing any concerning winds
at this time but definitely something to watch over the coming
days. Will note that during this period of time conditions will
be quite dry and unstable. -Muessle


&&

.AVIATION...Typical summer onshore flow pattern bringing in
marine stratus to the coast and reduced visibility in isolated
patchy fog. Nearly a 100% chance of MVFR CIGs along coastal
terminals through 22Z Fri with south to southwesterly winds.
Until 17Z there is a 70% chance of IFR CIGS. One limiting factor
to this though is that drier air at the surface remains and
there is a slight southeasterly flow in some coastal locations.
These conditions will repeat on Saturday morning.

Inland terminals will see minimal fluctuation with VFR
conditions under clear skies with westerly to northwesterly
winds. Areas within the Columbia River Gorge, any terminals
located near the Coast Range gaps, and Cascade foothill valleys
could see elevated gusts in the afternoon due to increased
westerly winds.

PDX AND APPROACHES...VFR with no concerns. -Muessle

&&

.MARINE...Benign conditions will continue over the coastal
waters through the upcoming weekend as winds remain around 10 kt
or less and seas hover between 2 and 4 ft, resulting in
conditions that are favorable for small craft. A more typical
summertime pattern returns on Monday and likely continues
through at least Wednesday of next week, bringing persistent
northerly winds that are strongest during the afternoon and
evening hours each day, especially to the south of Cape Falcon.
That being said, the probability of reaching small craft
advisory level wind gusts of 21 kt or stronger in the next few
days is only around 5-10% each day due to a relatively weak
surface pressure gradient in place. Seas should remain less than
5 ft on Monday before increasing to 5 to 7 ft late Tuesday into
Wednesday. Higher probability for small craft level winds on
Tuesday through Thursday. -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

www.weather.gov/portland

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