615
FXUS66 KPQR 171715
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1015 AM PDT Sun Aug 17 2025

.SYNOPSIS...High pressure continues to build through the week
with variable conditions early in the week. Persistent onshore
flow until later in the week when winds will become offshore as
a thermal trough develops.

&&

.SHORT TERM...Now through Wednesday...The synoptic pattern is
composed of a broad area of low pressure in the northeast
Pacific, and a developing high over the Rockies. The combination
of these two features will make for a dynamic system. In the
short term, the low will become anchored over southeast Alaska
and the islands of British Columbia through Monday. Weak
perturbations within the overall flow will continue the threat
of light showers and mixing. In general, showers will be
isolated to the coast, and the northern most portions of
northwest Oregon and southwest Washington. Models are in fairly
good agreement in location, but some are more robust than others
- like the NAM Nest that is putting significantly more rain
than other high- resolution models.

One slight shift in the forecast lies on Tuesday and Wednesday.
The surface pattern is pushing the parent low into inland
Canada, with the high building over the Rockies. The 850 mb
temperature profile is showing a deepening trough of cooler air
over the interior Rockies and over the Pacific, while over the
PNW, 850 mb temperatures continue to rise through Wednesday.
                   -Muessle

.LONG TERM...Thursday through Friday...Transitioning into
Thursday, the ridge will be amplifying with a thermal trough
forming over Oregon. A weak Omega blocking pattern is forming to
the north with two broad lows over interior Canada and the Gulf
of Alaska. With the thermal trough forming at the surface and
high pressure further inland, expecting winds to shift to the
east. Some downsloping will occur through the end of the week
which will cause additional heating and drying. On Friday, 850
mb temperatures will rise up to around 24 deg C. With this
vertically stacked temperature profile, easily could see
temperatures to return into the upper 80s and lower 90s in the
Willamette Valley. -Muessle

&&

.AVIATION...Largely VFR flying conditions expected across the
region, with sct-bkn clouds at 5-6 kft through this afternoon
and evening. Along the coast, a few isolated rain showers
cannot be ruled out, most likely at KAST, but any impacts are
unlikely and would be brief. Marine stratus this evening into
tonight will favor IFR/LIFR cigs and potentially restricted vis
after 00-06z Mon at coastal terminals, most widespread along the
central Oregon coast with lower confidence to the north.
Inland, VFR conditions are expected to continue, however there
remains a 10-20% chance of cigs falling to MVFR levels after 12z
Mon. Diurnal west to northwest winds rise to 5-10 kt today,
then ease to 5 kt or less overnight out of the south/southwest.

PDX AND APPROACHES...VFR flying conditions expected with
persistent sct-bkn clouds at 5-6 kft. Cloud cover again
increases tonight, with a 10% chance in cigs falling to MVFR
levels 12-18z Mon. Northwest winds around 5 kt will become light
and variable after 06-09z Mon. -Picard

&&

.MARINE...Relatively tranquil conditions are expected into next
week with light southwesterly winds and seas falling from 5-7
ft today to 3-4 ft by Tuesday, driven largely by a west-
northwesterly swell at 9-10 seconds. High pressure building over
the northeastern Pacific will see winds shift out of the
northwest to north by Tuesday night, with a 50-70% chance of
gusts exceeding 20 kt on Wednesday, and 70-90% on Thursday and
Friday. -Picard/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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