458
FXUS66 KPQR 040955
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
255 AM PDT Mon Aug 4 2025

.SYNOPSIS...Mean troughing will bring continued below-normal
temperatures through Thursday with cloudy mornings giving way
to afternoon sun inland. Clouds and chances for rain increase
Tuesday night into Wednesday, before building high pressure sees
a warming and drying trend Thursday through the weekend.

&&

.SHORT TERM...Now through Wednesday Night...An upper-level
trough centered over southeastern Alaska with surface high
pressure offshore in the northeastern Pacific will see continued
onshore flow and maintain below-normal temperatures through
midweek. An embedded upper shortwave moving onshore early this
morning will see enhanced onshore flow and marine overcast,
which could see clouds persist into the early afternoon even
across inland valleys, as on Sunday morning. Boundary layer
schemes often over-mix the lowest levels in scenarios like
this, and have therefore leaned cloudier this morning and
cooler this afternoon than the majority of guidance, yielding
afternoon highs in the mid to upper 70s inland and 60s along the
coast; if robust mixing does clear skies earlier, temperatures
inland could reach into the low 80s. Overnight lows look to
remain int he 50s across much of the region tonight.

By Tuesday, low-level flow turns increasingly southerly while
flow aloft returns to a more zonal pattern locally, aiding in
warming temperatures by a few degrees into the 80s across inland
valleys unless a thicker cirrus deck develops ahead of an
approaching frontal system. As troughing aloft deamplifies, a
filling surface low will track north of Vancouver Island and
bring its aforementioned surface front toward the coast. This
system will bring the best chance for widespread rain in some
three weeks from late Tuesday through Wednesday, although there
remains uncertainty around forecast rainfall amounts. Nearly
all global ensemble members now depict accumulating rain along
the coast as well as inland north of Corvallis/Albany, while the
southern Willamette Valley and adjacent Cascades are the most
likely to remain dry. Rainfall amounts at this point are favored
to be below 0.1" for most, and 0.1-0.3" in the northern Oregon
Coast Range and Willapa Hills, along the southwestern Washington
coast, and across the Cascades from Clackamas County north to
Mount St. Helens. Chances for a true wetting rain (>0.25") are
generally 20-60% in these areas, and less than 20% elsewhere.
Ongoing rain showers will keep overnight temperatures slightly
more mild Tuesday and Wednesday nights, and a few degrees cooler
Wednesday afternoon. -Picard


.LONG TERM...Thursday through Sunday...While cloud cover and
a few scattered rain showers may linger into Thursday morning
behind the departing system, a marked pattern shift will see
rising heights aloft atop resurgent surface high pressure over
the northeast Pacific. This flow regime will usher in a steady
warming and drying trend beginning Thursday and pushing
temperatures above normal by the weekend. By Sunday and next
Monday, 850-hPa temperatures of 20-25C could see surface
temperatures well into the 90s and approaching 100 degrees
across inland valleys, with 20-60% chances of highs exceeding
100F along I-5 from Portland/Vancouver southward. -Picard

&&

.AVIATION...VFR conditions continue across the airspace as of
10Z Monday. Expect conditions to begin to deteriorate by
11-13Z Monday as a blanket of high clouds move northeastward out
of the area, allowing for low stratus to develop. Current
guidance suggests a 50-70% chance for MVFR conditions along the
coast through most of the TAF period (lowest chances at KONP);
inland chances for MVFR conditions around 30-50% between 11-18Z
Monday. Highest relative confidence for MVFR CIGs inland at
KPDX, KTTD, KUAO, and KEUG. Inland terminals will return to VFR
in the afternoon. North to northwesterly winds under 10 kt
through the TAF period.

PDX AND APPROACHES...VFR conditions currently prevail. There is
a 30-50% chance for MVFR CIGs redeveloping between 11-18Z
Monday, then improving to VFR by the afternoon. Expect
northwesterly winds under 10 kt through the period. ~Hall

&&

.MARINE...Minimal change in the forecast as a persistent pattern
will maintain relatively calm seas. Seas remain 3 to 5 feet
through the week and into next weekend. Winds will be
northwesterly 10-15 kt with gusts as high as 20 kt along the
coast and the far outer waters through Monday. Due to the
northerly flow, the inner waters will see the gustier conditions
though will remain just below critical criteria.

On Tuesday, a low pressure system drops south into Haida Gwaii,
bringing southerly winds over the waters. Within the inner waters
there will once again be an increase in winds, but gusts are
still expected to remain 21 kts, Small Craft Advisory levels.
However, wind waves will still react and thus bring combined
seas to 4-6 ft at 10-12 seconds. ~Hall/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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