961
FXUS66 KPQR 212051
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
151 PM PDT Tue Jul 21 2026

.SYNOPSIS...Very hot temperatures today will persist overnight
into Wednesday. Highs in the mid to upper 90s expected inland
with chances of highs up to 100 degrees F on Wednesday.
Monsoonal moisture will move in on Wednesday which will
complicate the forecast. Thunderstorm and shower chances
increase on Wednesday, especially in the afternoon with
additional daytime heating. Widespread lightning not out of the
question. Showers persist into Thursday and cooler temperatures
expected through the remainder of the week.

&&

.SHORT TERM...Now through Thursday...Today has been on the hot
side as high pressure over the region has built. Overnight lows
were higher than forecast with temperatures reported around 65
degrees F in urban areas. This created a launching pad for
today`s highs where temperatures are n the widespread 90s inland
and in the mid to upper 50s along the Coast. Even along the
Cascades, some sites are reporting highs of 90-91 degrees as of
2 PM. Will see a continued warm up my a few more degrees today.
One caveat is in the southern Willamette Valley where some bleed
over monsoonal moisture is filtering in. Satellite is showing
cloud cover moving in which may inhibit some daytime warming
around Eugene and the foothills of the Willamette Natl Forest.
With that said, still increasingly hot and there appear to be
enough breaks where there is ample time for warming. Radar shows
virga also in the region. Overnight temperatures will fall but
are not expected to see significant relief outside of the coast.
These overnight temperatures combined with today`s high sparked
the need for additional Heat Advisories along the south
Washington Cascade and central Oregon Cascade foothills through
at least tonight.

Moving into Wednesday we are going to see a bit of a transition.
While some models would suggest the pattern is fairly cut and
dry, the overall pattern is actually quite messy which is
leading to some levels of uncertainty. While models want to
maintain the overall high pressure over the region, a
combination of monsoonal moisture influx and a low pressure
system off of the Oregon/California border will drive a much
more active weather pattern. Will see southerly flow maintaining
which, when combined with warm overnight temperatures, will once
again bring an influx of warm air to the region. Each model run
has shown the high temperature forecast increase steadily now
with multiple areas seeing forecast highs near or greater than
100 degrees F. However, that is not the whole picture as there
is that moisture to deal with. Will see higher than normal
humidity on Wednesday which will make the air appear hotter
than it normally would if the atmosphere was drier. Major
HeatRisk exists through much of the Willamette Valley.

This incoming moisture will not only impact how hot conditions
feel, but will also change the sensible weather. High
resolution models have begun to show more widespread and
potentially intense precipitation starting as early as Wednesday
morning with higher confidence on it starting Wednesday
afternoon. One thing to note though is that it likely will not
be in the form of rain, but rather as thunderstorms. Convective
indices like Most Unstable CAPE (MUCAPE) are showing elevated
convection around 1500 J/kg over the Cascades and even some
inland sites. This is only amplified when taking into account
daytime heating which would help us surpass any caps that form
at the surface. Therefore there is around a 15-20% chance of a
widespread thunderstorm situation over all of northwest Oregon
and southwest Washington. Over the Cascades though that is
higher with closer to a 30-35% chance. The highest probabilities
will be over the Willamette Natl Forest on Wednesday afternoon
and evening. Some models are showing a few cells popping up on
Wednesday morning along the coast, but there is much higher
consensus on the afternoon time frame. With this in mind, these
storms are forecast to be wet with limited wind. However,
widespread lightning (similar to last week) cannot be ruled out.
It is critical that if you hear thunder or see lightning that
you take cover immediately inside of a sturdy structure, get off
of the water, and limit outdoor activities like golfing or
playing baseball.

Storms and showers are expected to persist overnight, though
will become lighter as we lose daytime heating. Isolated showers
into Thursday morning. -27



.LONG TERM...Thursday night through Tuesday...By Thursday, the ridge
begins to weaken as a broader trough moves toward the Pacific
Northwest. This should promote a return to more noticeable
onshore flow and begin a gradual cooling trend that carries into
late week. Temperatures are still likely to remain somewhat
above seasonal normals Thursday and Friday, but not to the
degree seen earlier in the week. Looking beyond Friday, forecast
guidance currently does not show a strong signal for meaningful
precipitation, while temperatures trend toward the lower 80s
through the weekend and into early next week. -12


&&

.AVIATION...VFR flight conditions expected inland today with
BKN/OVC high clouds in central OR. Any lingering marine stratus
along the coast should dissipate and improve to VFR by 18-19z Tue.
A resurgence of marine stratus is likely again tonight into
Wednesday morning with IFR/LIFR cigs. At KONP, stratus returns
after 00-03z Wed with LIFR conditions favored with a 40-60%
chance. Stratus could return at KAST anytime after 06z Wed with a
20-40% chance of IFR and LIFR conditions, higher chances after 12z
Wed. North to northwest winds generally less than 10 kts.

KPDX AND APPROACHES...VFR conditions prevail with northwest winds
less than 8 kts. -03

&&

.MARINE...A typical summertime pattern will continue through the
middle of this week with persistent north to northwest winds over
the coastal waters. Winds then shift southwest to westerly
Thursday into the weekend as weak low pressure develops over the
waters. Winds will remain light less than 10-15 kts. Seas will be
3-6 ft at 8-9 seconds through the weekend.

On Wednesday, there is a chance for showers and thunderstorms
across all of the waters through the majority of the day and
overnight hours. There could be frequent lightning and gusty and
erratic winds with any thunderstorm that forms. -03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 11 PM PDT Wednesday for ORZ108>115-120>122.
     Heat Advisory until 11 PM PDT this evening for ORZ117-124.
WA...Heat Advisory until 11 PM PDT Wednesday for WAZ204>210.
PZ...None.
&&

$$

www.weather.gov/portland

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