929
FXUS66 KPQR 162143
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
243 PM PDT Fri May 16 2025

.SYNOPSIS...A progressive weather pattern will bring periods of
light rain through the weekend and into early next week. Expect
temperatures to remain slightly below average during this period.
Rain showers increase later tonight through Saturday, along with a
10-20% chance of thunderstorms Sat afternoon. Lingering showers into
Sunday, though most areas likely drier. Temperatures trending
warmer, upper 60s to lower 70s, toward the end of next week.

&&

.DISCUSSION...Tonight through Friday...Mostly cloudy skies with
light rain showers, mainly along the north coast, will continue
through this evening. Temperatures this afternoon are warming into
the mid-60s inland, still around 5 degrees below normal for mid-May.
Later tonight, expect showers to increase in intensity and become
more widespread as the next weather system approaches. A shortwave
trough riding along the northern Pacific jet slides across the
region, digging toward northern California by early Saturday
morning. Rain showers will likely be heaviest through the early
morning hours as the atmospheric moisture is at its deepest and the
upper trough is overhead. Chances for showers will continue through
the rest of the day, with a small (10-20%) chance for a rumble of
thunder through Saturday afternoon/evening. No strong thunderstorms
expected. With continued onshore west to northwesterly flow aloft,
rain will be most persistent along the higher terrain, especially
the western slopes of the Cascades and Cascade foothills. Total
rainfall amounts from now through Saturday night are expected to
range from around 0.10 to 0.40 inch for much of the lowlands, and a
bit more substantial for the higher terrain, around 0.5 to 1.0 inch,
with a 20-30% chance of exceeding an inch of rainfall over 48-hours
for a few locations in the Cascades.

Conditions trend drier on Sunday, though light showers persist into
the afternoon as troughing along the British Columbia coast drops
south, developing into a cutoff low east of the Cascades by Sunday
evening. Transient upper level ridging builds over the region Sunday
night with decreasing clouds, and some sunshine by later Sunday
afternoon into the evening. Temperatures remain slightly below
average into early next week. Another round of light rain is now
likely on Monday as a weak front crosses the region. Zonal flow with
embedded upper level disturbances could maintain light showers into
Tuesday, again mainly over northern portions of the forecast area.

Agreement amongst the models and their ensembles degrades middle to
end of next week with cluster analysis showing split pretty equally
between ridging and troughing. NBM guidance though continues to
suggest temperatures gradually warm closer to average toward the
latter part of next week, along with precipitation probabilities
generally 15% or less Wednesday through Friday. /DH

&&

.AVIATION...West to southwest winds aloft as a weather system
approaches and moves through the region, becoming west to
northwest by 12z Saturday. Predominately VFR conditions inland
through 06-09z Saturday. Along the coast, predominately MVFR
conditions with occasional IFR conditions expected though a few
hours of improved conditions possible through 03z Saturday.
Another frontal system is expected to bring a round of widespread
showers and the return of MVFR/IFR cigs along the coast by 03-06z
Saturday and MFR cigs inland by 06-09z Saturday. Southerly to
southwesterly winds at less than 10 kt will continue at all
terminals through much of the period, turning out of the north to
northwest behind the frontal boundary.

PDX AND APPROACHES...VFR cigs around FL3300-5000. Another frontal
system will bring additional rain showers and likely MVFR cigs
around FL1500-3000 after 06-09z Saturday. North to northwest
winds less than 10 kt, becoming westerly after 12z Saturday. -HEC

&&

.MARINE...Southwesterly winds over the waters Friday afternoon
will shift northwesterly tonight into Saturday as a front passes
through the region. Winds through early Saturday morning around
8-15 kts with gusts mainly below 20 kts. However, a localized area
of wind gusts up to 25 kts exists in portions of zones PZZ271 &
PZZ251 through around 5 PM PDT. Winds increase Saturday late
morning behind the frontal passage to 17-22 kts with gusts up to
25-30 kts through Sunday morning. A Small Craft Advisory has been
issued for 11 AM Saturday through 11 AM Sunday. Seas remain around
5-9 ft at 10-12 seconds through the weekend.

Another frontal passage is forecast on Monday. Winds shift
southerly with another round of Small Craft wind gusts 25-30 kts
expected (70-90% chance). Seas decrease to 5-7 ft at 10 seconds
Monday before an increasing westerly swell builds waves to around
9-10 ft at 12-13 seconds on Tuesday. -HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 11 AM Saturday to 11 AM PDT Sunday for
     PZZ210-251>253-271>273.
&&

$$

www.weather.gov/portland

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