803
FXUS66 KPQR 242158
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
258 PM PDT Sat May 24 2025

.SYNOPSIS...Dry conditions and above normal temperatures persist
the rest of this afternoon into Sunday with light winds.
Chances for light rain showers return to the region Sunday
evening/night into Monday, with most locations likely observing
at least some measurable rain. Trending warm and dry again from
Tuesday onward, with the warmest temps of the year so far
possible on Wednesday.

&&

.SHORT TERM...Tonight through Sunday Night... A transient ridge
of high pressure continues to progress east of the Cascades
today with a switch to southwesterly flow aloft come Sunday.
Still, conditions will be rather similar through tomorrow
(Sunday) afternoon aside from slightly cooler temps due to
increasing high clouds - a modest 4-7 degree drop for most
inland locations. The main exception will be in the Cascades
where there is still a 15-30% chance of rain showers in the
Cascades during the late afternoon hours (after ~2-3pm),
increasing to 40-60% in the evening due an an approaching
frontal boundary. There`ll also be a slight chance (10-15%) for
thunderstorms near the Cascade crest-line however models depict
an upper level flow pattern that is more southwesterly rather
than south-southwesterly. This flow regime should generally keep
convection east of the Cascade crest which is currently what is
shown in almost all high resolution model guidance like the
HREF, UW-WRF, and MPAS. Even if an isolated cell or two is able
to initiate along the immediate crest, it would quickly shift
northeastward into central/eastern Oregon and Washington.

The axis of the incoming shortwave trough and accompanying frontal
boundary finally move overhead Sunday night into Monday morning
bringing cooler and cloudier conditions along with light rain
showers for most locations, mainly focused in the morning hours.
The latest NBM shows a 60-90% chance for at least measurable
rain (at least 0.01") across all of northwest OR and southwest
WA Sunday night through Monday afternoon, with the highest
probabilities for the coast, Coast Range and Cascades. While
confidence is fairly high at least some measurable rain will
occur, confidence is low regarding exact rain amounts as some
ensemble guidance continues to show higher amounts around
0.2-0.3". The NBM is still showing a 10-25% chance for 0.25" of
rain or more along the coast/Coast Range, except 30-45% in the
Cascades and 5-10% or less elsewhere during this same time
period. Fortunately, conditions dry out Monday night as the
weakening front moves well east of the Cascades and heights
begin to rebuild aloft. -Schuldt/TK


.LONG TERM...Tuesday through Friday night...Deterministic and
ensemble guidance are in good agreement depicting dry weather
and a rapid warming trend Tuesday into the middle of the week
with potentially the hottest temps of the year so far Wednesday
come afternoon. WPC`s cluster analysis for 500 mb heights and
anomalies continue to suggest 500 mb heights will be well above
normal as an upper level ridge amplifies over the Pacific
Northwest and low-level flow turns offshore; this latter
component is key to the significant jump in temperatures Tuesday
to Wednesday. Confidence is now very high (>80-90%) temps will
warm into at least the mid 80s over the interior lowlands and
into the 70s at the coast Wednesday afternoon. In fact, the
central/northern Willamette Valley, lower Columbia and
Portland/Vancouver metro are likely to warm into the upper 80s
to low 90s. The probability for high temps above 90 degrees is
around 10-30% for most inland valley locations, except around
40-60% across the greater Portland/Vancouver metro and lower
Columbia where the warmest temps are expected. HeatRisk is now
in the Moderate category for the aforementioned warmest
locations and in the Minor category elsewhere. Those who chose
to seek relief by swimming in rivers and lakes should be very
careful and ideally wear a wetsuit as water temps are still cold
enough to result in cold water shock.

The forecast becomes a little more uncertain Thursday onward as
guidance starts to diverge on the eastward progression of the
upper level ridge over the area, the degree of amplification, as
well as the eastward progression of a Pacific front that may
attempt pushing inland. There is at least a high degree of model
confidence Thursday will be a cooler than Wednesday by ~6-12
degrees due to a return of low-level onshore flow and/or
potential frontal influence, but inland locations should end up
somewhere between the mid 70s and mid 80s depending on the
timeliness of the previously mentioned feature. Ensembles then
show a ridge of high pressure building over western CONUS late
next week although there`s decent uncertainty in the
longitudinal placement of this feature which will heavily
modulate temperatures. For now at least, the majority of
solutions support above normal temperatures prevailing.
-Schuldt/TK

&&

.AVIATION...VFR conditions under clear skies across all terminals
through Saturday evening. Expect west-northwesterly winds across the
area this afternoon, generally under 10 kt. Tonight, marine stratus
returns along the coast due to increasing moisture from onshore
flow. Will begin to see FEW/SCT low clouds along the coast around 05-
06z Sun, with MVFR CIGs likely (60-80% chance) after 09-11z Sun. VFR
conditions prevail inland tonight, with a 15-30% chance for MVFR
CIGs across the Willamette Valley between 10-18z Sun. Winds shift
southwesterly overnight across the region ahead of a weak front,
but remain light.

PDX AND APPROACHES...VFR conditions with high clouds through the TAF
period. Guidance suggests a 15-25% chance for MVFR CIGs between 12-
17z Sun. West-northwesterly winds around 5 kt or less through
tonight, turning southwesterly by Sunday afternoon.      -Alviz

&&

.MARINE...Weak high pressure offshore will maintain northerly to
northwesterly winds under 10 kt across the waters through
Saturday evening. Tonight, winds shift south-southwesterly ahead
of an approaching weak front. This front will push through the
waters Sunday evening, increasing southerly winds to 10-15 kt
with gusts up to 20 kt. Winds weaken and shift more westerly
behind the front on Monday. Seas 3-5 ft will build to 6-8 ft at
11 seconds Sunday as the front moves through.

A Small Craft Advisory has been issued for the Columbia River Bar
between 1 AM to 6 AM Sunday for a very strong ebb current. This
will result in 7-8 ft seas for the Bar early Sunday morning.
                                                      -Alviz

&&

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

$$

www.weather.gov/portland

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