245
FXUS66 KPQR 280407
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
907 PM PDT Fri Jun 27 2025

Updated aviation discussion.

.SYNOPSIS...A pattern change begins on Saturday as we transition
to well above normal temperatures for the latter half of the
weekend into early next week. Confidence remains moderate to high
for inland valley temperatures to approach or exceed 90
degrees Sunday through Tuesday - highest temperatures Monday.
Another concern remains for the possibility (15-35% chance) of
thunderstorms over the Oregon Cascades Monday and Tuesday.
At least temperatures likely trend cooler (low to mid 80s)
by the middle to end of next week.

&&

.SHORT TERM...Now through Sunday Night...A sharp warming trend
will take place next couple of days as a ridge of high pressure
amplifies overhead. Starting on Saturday the persistent morning
cloud cover which has kept a damper on temperatures the last
several days thanks to modest onshore flow will be less
prevalent headed through the afternoon hours as northerly flow
develops. For locations like the Portland/Vancouver metro
temperatures likely rise 5-8 degrees into the upper 70s to low
80s while this jump is less noticeable in the southern
Willamette Valley where skies have cleared more readily in past
days. Models show excellent agreement in the development of
offshore flow just above the surface Saturday night into Sunday
helping to drive temperatures even higher for Sunday
afternoon. A near surface thermal trough surges northwest Sunday
as well, but the axis of this feature should stay pinned closer
the Cascades keeping at least some degree of N/NNW flow near
the surface and holding temperatures somewhat in check. The NBM
projects around a 30-50% chance for highs to meet or exceed 90
degrees Sunday afternoon across the Willamette Valley, highest
along the foothills of the Cascades (locally 60-80%), but keeps
these probabilities lower Portland proper northward (only
10-20%) likely due to that aforementioned N-NNW surface flow
kicking in during the afternoon hours. Given the overall set-up and
tight NBM ensemble temperature distribution confidence in the
forecast through the weekend is high - it`s going to get warm.
-Schuldt

.LONG TERM...Monday through Thursday...Monday will likely be
the hottest day of the week with highs across the Willamette
Valley and other inland valleys reaching to the low 90s. Due to
overnight lows in the 50s to low 60s Heat Risk should only peak
in the moderate category. Temperatures drop a few degrees for
Tuesday as more of an onshore component returns to the low-
level flow but we`ll still be 6-10 degrees above normal for
early July. Probabilistically, there is a a 75-90% chance to
exceed 90 degrees on Monday for the interior valleys, falling to
a 40-60% chance Monday.

While the primary concern remains heat related early next week,
starting on Monday we are still on the lookout for possible
thunderstorms in the Cascades, especially in the late afternoon
and evening Lane County Cascades southward. This is all thanks
to a weak upper-level closed low off the coast of California
increasing mid-level moisture (700-500mb) across portions of
the region leading to increasing instability. At this time,
chances have held in the 15-30% range for T-storms mainly
focused along the Cascade crests where terrain forcing is
favorable to spark activity. Given the location of the upper-
level low and moisture plume, Lane County southward will have
the have the best chances of seeing at least isolated
development. Should it shift northward, those chances could
extend upward towards Mt. Hood but this appears to be a outlying
scenario at this time. Could see thunderstorms again on
Tuesday, although with less confidence in the exact placement.

Temperatures will cool down a bit for the middle of the week
but still stay warm. Highs in the Willamette Valley will likely
stay in the low to mid 80s through midweek. Overnight
temperatures will also be warmer than what we have seen
recently, generally staying in the 50s to low 60s. -Schuldt/Hall


&&

.AVIATION...Predominately VFR conditions across NW Oregon and SW
Washington as of 04z Sat, though continued onshore flow will
produce another round of widespread stratus. Along the coast,
patchy stratus remains and is expected to become more widespread
with MVFR/IFR ceilings by 06-08z Sat. Occasional LIFR ceilings
could be observed, as well. Stratus begins forming inland by
10-12z Sat with MVFR ceilings likely through 17-20z. However,
stratus deck is expected to be thinner than previous nights, so
inland terminals could see conditions bouncing between low end VFR
and high end MVFR, or a shorter period of prevailing MVFR. Winds
remain light and from the west/northwest through around 15-18z
Sat. Then, building high pressure begins shifting winds northerly,
with offshore flow taking hold through the rest of the TAF period
into Sunday.

PDX AND APPROACHES...Prevailing VFR conditions through 10-12z Fri.
Then a 50-60% chance of MVFR ceilings, becoming

&&

.MARINE...Onshore flow persists with little change in the
forecast. On Saturday, conditions will begin to shift as a ridge
of high pressure slowly builds over the Pacific and a trough to
the north shifts eastward. The combination of these two features
will cause northerly winds over the waters to increase. This
typical summertime pattern will bring winds to 15-20 kt with gusts
up to 25 kt through all of the waters spreading from south to
north. Given the timing difference between zones, each as a
separate Small Craft Advisory, though that may shift if timing
becomes into better agreement. On Sunday through Tuesday
temperatures will rise considerably and a thermal trough forms.
This temperature difference will cause winds to peak on Monday
morning with gusts up to 30 kt in PZZ273 and 253.

Seas will be predominately west-northwest with a northerly wind
wave kicking in on Sunday night. At this time, the wind wave will
be the dominate feature. However, conditions will see little
change as overall they will not rise considerably. Looking at seas
of 5-6 ft at 9 seconds on Saturday building to 7-9 ft at 9 seconds
on Monday. Seas will then ease as the ridge decays. -Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 8 PM Saturday to 2 PM PDT Sunday for
     PZZ252-272.
     Small Craft Advisory from 2 PM Saturday to 2 PM PDT Sunday for
     PZZ253-273.
&&

$$

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