296
FXUS66 KPQR 302226
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
326 PM PDT Sat Aug 30 2025

.SYNOPSIS...A cutoff low lingering offshore of northwestern
Oregon and southwestern Washington will bring continued
seasonable temperatures through Labor Day Weekend with morning
incursions of marine clouds giving way to breaks of afternoon
sun. Building high pressure will yield a warming trend early in
the week, with the potential for high temperatures reaching the
90s and Moderate to Major HeatRisk Tuesday through at least
Thursday across inland areas. Increasing chances of scattered
showers and isolated thunderstorms midweek.

&&

.SHORT TERM...Saturday Afternoon through Monday...Satellite
imagery Saturday afternoon depicts two classic low pressure
systems, one just west of the Oregon/Washington coast and one
farther southwest in the Pacific, centered around 40N 155W. The
low pressure system just to the west of our coast will remain
fairly stationary through Monday, only moving slightly to the
northwest. Today it is closest to the NW Oregon and SW
Washington coast, and it is producing showers over the coastal
waters that are pushing just along the coast. Most of these
showers are drying and becoming virga as soon as they reach
land, though a few observation stations have reported a trace to
0.01 inch of rain throughout the day. Mid to upper level clouds
are streaming across much of the region, with along with the
cooler air funneled into the region from the upper low are
helping to keep temperatures on the cooler side. Observed
temperatures as of 3 PM are only in the upper 60s for the SW
Washington lowlands, mid 70s north of Salem, and upper 70s to
low 80s south of Salem where there is little to no cloud cover.
Conditions tomorrow into Monday will be similar with just less
widespread cloud cover, leading to slightly warmer temperatures
each day. Marine stratus formation is likely each night into the
morning hours, with stratus intrusion possible through Coast
Range gaps each morning. -HEC

.LONG TERM...Tuesday through Friday...The forecast becomes more
uncertain in the long term. Ensembles indicate the low pressure
system off of the coast will begin retrograding on Tuesday, with
high pressure currently over the Great Basin beginning to move
west into Oregon and Washington. This will allow temperatures to
warm a bit on Tuesday into the upper 80s to low 90s. However,
ensembles are in good agreement of a compact closed low moving
into central California late Monday/early Tuesday, then moving
north through California into Oregon sometime after that. The
uncertainty now comes into play in the timing of when the low
will move into Oregon as well as the strength of it, both of
which could impact how far west the high pressure can spread
into the area and therefore whether temperatures continue
warming into midweek or remain steady. Additionally, this low
will produce shower and thunderstorm chances over Oregon, but
due to the previously mentioned uncertainty, that introduces
uncertainty in location and timing of shower and thunderstorm
chances. If showers/thunderstorms form, this would produce cloud
cover that could also impact the potential for warming
temperatures.

The 13z NBM run has toned down on the warming temperatures, with
deterministic highs remaining in the low 90s for Wednesday and
Thursday. Probabilities for reaching 95 degrees for both days
have also decreased a bit to 40-55% for inland valleys.
Overnight temperature forecast still remains on the slightly
warmer side with many inland locations forecast to remain above
60 degrees. There is still widespread Moderate HeatRisk for
inland areas for Tuesday through Thursday, but Major HeatRisk is
now more limited to the Portland and Salem urban areas and the
Columbia River Gorge. These temperatures could still impact
vulnerable populations, especially those spending extended time
outdoors or those without adequate air conditioning.
By Friday, temperatures are expected to begin a downward trend
into the 80s, though there`s still a 10-25% chance temperatures
could be as warm as 95 degrees. -HEC

&&

.AVIATION...A weak upper low offshore the Washington and Oregon
coast will support a deepening marine layer tonight and return MVFR-
IFR stratus to the coast and interior valleys tonight into Sunday
morning. Overnight stratus is expected to have more widespread
interior coverage Sunday morning compared to what was observed
Saturday morning. The probabilities for ceilings below 1000 ft
along the coast exceed 50% around 06z Sunday and increase to 70%
11z Sunday. The probability for ceilings below 1500 feet exceeds
30% in the Willamette Valley at 14z Sunday with clearing shortly
after 19z Sunday.

PDX AND APPROACHES...There is a 30-40% probability of MVFR
ceilings returning to the area 13z Sunday. Any stratus that forms
should clear to VFR around 20z Sunday. Light winds of 5 kt or less
will prevail.~TJ

&&

.MARINE...Low pressure will maintain light winds across the
coastal waters through Monday. High pressure builds Tuesday and
Wednesday for increasing north winds. The winds will be strongest
in the afternoons and evenings, especially to the south where the
surface pressure gradient will be the strongest. The north wind
gusts will flirt with small craft conditions Tuesday and Wednesday
afternoons where there is a 40% chance of wind gusts greater than
20 kt. Seas will be below 4 ft through Monday, with an increase
in wind waves building seas to 5-6 ft Tuesday through
Thursday.~TJ

&&

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

&&

$$

www.weather.gov/portland

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