Lake Oswego, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

950
FXUS66 KPQR 222216
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
316 PM PDT Thu May 22 2025

.SYNOPSIS...A warming and drying trend takes hold across the
region for much of this Memorial Day weekend. More active
weather returns late Sunday into Monday, including a 15% chance
for Cascade thunderstorms, however, forecast confidence
degrades dramatically by Wednesday of next week.

&&

.SHORT TERM...Tonight through Sunday...Radar and satellite
imagery shows lingering shower activity has remained fairly
isolated this afternoon, primarily confined to the higher
terrain of the coast range/Cascades, likely persisting into the
evening hours before drier weather returns. Another weak and
progressive trough will pass over the region early on Friday
with almost all areas remaining dry locally due to a lack of
moisture/upper-level forcing. By Friday afternoon, heights
aloft will begin to rise in earnest as longwave ridging begins
to build over much of the western CONUS. Temperatures jump into
the 60s and 70s Friday afternoon which is right around normal.
This warming trend continues into Saturday as well with the
axis of the amplifying upper-level ridge passing west to east
over the Cascades leading to another 5-8 degree jump in high
temperatures. Confidence is high for maximum temperatures rising
into the mid 70s to near 80 along the I-5 corridor and other
inland valleys Saturday afternoon, above normal for late May.

Late Sunday chances begin to increase for a brief breakdown in
upper ridging as an increasing number of ensemble and deterministic
models favor a negatively-tilted shortwave trough undercutting
the ridge, before potentially becoming cutoff over California.
Given the warm antecedent conditions and advection of a mid-
level moisture layer preceding the trough, thunderstorms remain
a possibility (15-20%) late Sunday afternoon, mostly near the
crests of the Cascades eastward. Models like the GFS/NAM
currently show around 200-600 j/kg of MUCAPE in this region but
the exact timing of shortwave forcing will determine the extent
of convective development; a delay of this feature further into
the evening hours would keep activity weaker and pushed to the
east. Still, it`s definitely worth paying attention to if you
plan on venturing outdoors for the holiday weekend, especially
the Cascades.

.LONG TERM...Monday through Thursday...Ensemble and
deterministic guidance generally depict the axis of the
aforementioned upper-level trough with the attendant cut-off
low to our south passing overhead on Monday leading to a slight
chance for showers in the interior valleys but better
probabilities for activity along the coast/coast range and
Cascades due to more advantageous orographic forcing. Still,
exploring the NBM an other ensemble products overall rainfall
accumulation during this period looks rather low, <0.05-0.1"
for the Willamette Valley, 0.05-0.2" coast/coast range, and
0.1-0.3" Cascades. Resurgent ridging into Tuesday would then see
a quick return to warm and dry weather across the region. Then,
confidence rapidly decreases Wednesday and beyond as ensemble
spread increases dramatically. Persistent ridging could see a
prolonged period of warm to hot temperatures and dry weather
continue (50% of ensemble members), while a breakdown of the
ridge could instead see a return to cooler and wetter conditions
(also ~50% of ensemble members). This has resulted in a nearly
30 degree temperature spread (ranging from 65 to 95 degrees)
between the NBM 10th and 90th percentile for the potential high
on Wednesday. The current forecast sits in between (upper 70s
to mid 80s) with hopefully better model agreement in the coming
days increasing forecast confidence. -Schuldt

&&

.AVIATION...Onshore flow will maintain broken to overcast mid
level clouds through tonight, with more clearing expected on
Friday. As of 20z Thursday, predominately VFR conditions with MVFR
CIGs lingering at a few locations. Coastal sites have a 50-60%
chance of MVFR CIGs returning around 04-06z Friday. Winds remain
onshore and generally less than 10 kt. /DH

PDX AND APPROACHES...Predominately VFR conditions expected
through the TAF period with broken mid level clouds. Northwest
winds expected around 4-6 kts. /DH

&&

.MARINE...Weak high pressure offshore will maintain north to
northwesterly breezes across the coastal waters into the weekend.
Winds generally remain below 10-15 kt, though inland daytime
heating could drive the diurnal strengthening of the pressure
gradient, allowing winds to gust up to 20 kt along the nearshore
waters. Seas will persist around 3 to 4 ft through Saturday. By
early Sunday, winds turn southerly ahead of a weak front,
increasing through the day, but expected to remain below 20 kt. A
northwest swell will also build seas to around 6 to 7 ft. /DH


&&

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

$$

www.weather.gov/portland

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