143
FXUS66 KPQR 132124
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
224 PM PDT Thu Aug 13 2026

.SYNOPSIS...Warm and dry conditions expected through the
weekend with persistent onshore flow. Skies become hazy this
afternoon as some wildfire smoke drifts over the area. Slight
chance (10-20%) for thunderstorms or showers over the Cascades
Friday and Saturday afternoons, with the highest chances along
the crest of the Cascades.

&&

.DISCUSSION...Tonight through Wednesday...Upper level
troughing remains over the region with onshore flow in the
lower levels. One nuance, however, is in the mid-levels of the
atmosphere (5,000-10,000 ft above ground), where forecast
soundings are showing light easterly winds. This is resulting in
some smoke from the Grasshopper, High Lava, Mitchell Fires to
drift into the central and northern Willamette Valley. As the
evening progresses, some of this smoke will likely mix-down to
the surface. However, this smoke is expected to be short-lived
as winds from the west/northwest return tonight into Friday
morning and push smoke eastward and clear the air once again.

By Friday, the upper level trough broadens even further off the U.S.
West Coast. As more southerly flow aloft returns over the area, will
see increasing instability and monsoonal moisture that will support
a 10-20% chance for thunderstorms across the Cascades both Friday
and Saturday afternoons/evenings, with the highest chances
along the crest of the Cascades. Otherwise, the general airmass
remains too dry to support any widespread precipitation from
this trough. Guidance suggests high confidence for near to
slightly above average temperatures for mid-August through the
weekend, with afternoon highs warming into the mid to upper 80s
across interior valleys. By Sunday, there is increasing confidence
of the upper trough offshore becoming more elongated with low
pressure dropping south, well off the California coast. This
could allow for upper ridging over the intermountain west to
shift slightly west, nudging into the Pacific NW. But the main
axis of the ridge is expected to stay eat of the region.

Cluster analysis of 500 mb heights continues to show a wide
range of the magnitudes and placements of an upper level trough
offshore. Still, a slight cooling trend to closer to average
temperatures is possible by the middle of next week with no
precipitation in the forecast.

&&

.AVIATION...Westerly flow aloft becomes southwesterly as an upper
level trough moves slowly over the airspace, with north/northwest
flow persisting at the surface. This scenario is resulting in a
rather interesting set up for the airspace as a whole. For the
coast, MVFR marine stratus with a 50% chance of conditions clearing
to VFR for a few hours through 00Z Fri. If VFR conditions develop,
expect MVFR/IFR conditions to return around 00Z-03Z Friday and
persist through around 17Z Friday if not longer.

Inland locations generally VFR. However, through 06Z Friday,
smoke will likely mix down at times and could impact visibilities.
Smoke in the mid levels could impact slant range visibilities anytime
through 06Z Friday for inland locations from KSLE northward. Expect
MVFR conditions to return for locations south of KSLE starting
around 12Z-14Z Friday as marine stratus is expected to return.

North to northwest winds increase to 8-10 kts after 21Z Thursday,
before becoming less than 6 kts after 05Z Friday.

KPDX AND APPROACHES...Generally VFR conditions through the
remainder of the TAF period. However, through 06Z Friday, smoke
will likely mix down at times and could impact visibilities. Smoke
in the mid levels could also impact slant range visibilities anytime
through 06Z Friday. North to northwest winds increase to 8-10 kts
after 21Z Thursday, before becoming less than 6 kts after 05Z
Friday. /42

&&

.MARINE...No significant changes in the overall pattern as high
pressure offshore will continue to support northerly winds along
with fairly benign conditions across all waters into the weekend.
Winds from the north to northwest with gusts less than 21 kts will
continue through at least the weekend, with wind driven seas expected
to remain around 3 to 6 ft. /42

&&

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

&&

$$

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