369
FXUS66 KPQR 170922
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
222 AM PDT Mon Aug 17 2026

.SYNOPSIS...Seasonably warm and dry conditions expected through
much of the week with morning clouds and afternoon clearing.
Winds generally out of the west to northwest, strongest in the
afternoon and along the Central Columbia River Gorge and Upper
Hood River Valley. Next chances for light showers arrive Friday
into next weekend.

&&

.DISCUSSION...Now through Saturday...Minimal changes to the
forecast. Seasonably dry and warm conditions continue through
the week with minimal weather impacts. The large-scale pattern
remains stagnant through the period, with broad and relatively
flat upper-level ridging over the majority of CONUS and a weak,
positively-tilted upper-level troughing over the northeast
Pacific. This pattern will support continued onshore flow,
maintaining near-normal daily high temperatures in the 80s
within inland valleys and 60s along the coast, and overnight
lows in the 50s across the region. Mornings will be
characterized by clouds, especially along the coast, which will
tend to clear by the afternoon. Light west to northwest winds
will, peaking each afternoon. The strongest winds are likely to
be along the Central Columbia River Gorge and Hood River Valley,
but impacts are not anticipated.

The majority of ensemble members are in agreement that upper-
level ridging over the Rockies and Great Basin will build late
in the workweek, which would favor a brief warm-up on Thursday.
However, ensemble guidance continues to show the upper-level
trough over the northeast Pacific shifting onshore Friday into
the weekend, resulting in slightly cooler temperatures and winds
coming from the south/southwest. Chances for showers also
increase to 10-25% across the region during this time, with the
highest chances over the Coast Range and Cascades. However,
there is still high uncertainty in the timing and potential rain
amounts. A weak front at the end of the week would have a hard
time counteracting the dry airmass in place, making accumulating
rainfall unlikely and keeping most places dry.       -10/36

&&

.AVIATION...Through 06z Tuesday...VFR flying conditions
currently in place across the airspace will give way to
increasing MVFR chances as low stratus develops initially along
the coast and potentially within inland valleys tonight. There
is high confidence (70-90% chance) in conditions deteriorating
to IFR at coastal terminals as low stratus develops by 09-12z
Mon, while confidence in vis restrictions is lower. There
remains high uncertainty if low cloud will be able to penetrate
inland; the highest confidence (50-60% chance) for MVFR cigs is
along the lower Columbia River into Portland-area terminals
excluding KHIO, while chances are lower (30-50%) at Willamette
Valley terminals. Chances for MVFR cigs rise above 50% in the
hours around sunrise, 11-13z Mon, at KPDX/KTTD, and persist
through much of the morning.

By 16-18z Mon, diurnal mixing will favor clearing skies and
lifting cloud bases, with prevailing VFR again very likely at
inland terminals. Along the coast, low clouds will be slow to
erode, with VFR conditions most likely to be limited to the
mid-afternoon, if at all; there are modest (25-35%) chances
that MVFR cigs may persist through the afternoon.

Light north to northwest winds tonight will build to 5-10 kt at
inland terminals and to 10-15 kt with gusts near 20 kt along
the coast by 17-19z Mon. Winds ease again late in the period.

KPDX AND APPROACHES...High confidence in continued VFR
conditions through at least 08-10z Mon beneath sct-bkn high
clouds. Only moderate confidence in the potential for MVFR cigs
with chances peaking at 50-60% from 13-17z Mon. High confidence
in VFR cigs as diurnal mixing erodes low cloud coverage by
18-19z Mon. Northwest winds ease below 5 kt tonight, then build
to 5-10 kt by midday Monday.        -36

&&

.MARINE...A largely stagnant pattern continues through much of
the week with high pressure offshore supporting northerly to
northwesterly winds of 8-15 kt and afternoon gusts up to 20 kt.
Weak low pressure moving over the northeast Pacific Friday into
the weekend will shift winds out of the south to southwest
across the waters, but chances for gusts exceeding 21 kt remain
low, only 5-10%. Seas of 3-6 ft persist through the period.
Increasing periods of 12-14 sec on Tuesday-Wednesday may result
in a moderate risk for sneaker waves along the coast. Caution
should be used when in or near the water.      -10/36

&&

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

&&

$$

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