Herman Creek Trail, Oregon Weather Forecast Discussion

061
FXUS66 KPQR 290425 AAA
AFDPQR
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
925 PM PDT Sun Sep 28 2025
...Updated aviation discussion...
.SYNOPSIS...Dry conditions today become wet and cool for the
work week. Multiple frontal systems will bring periods of
widespread rain and breezy winds to the region. The first will
be Monday, followed by the strongest system Tuesday through
Wednesday, with unsettled conditions continuing through Friday.
&&
.DISCUSSION...Sunday Afternoon through Saturday...Satellite
imagery early Sunday afternoon shows the first of a number of
frontal systems approaching the PacNW, situated around 130 W
longitude over the eastern Pacific. Mostly clear skies are being
observed currently, except for marine stratus intrusion along
the coast. This will allow for one more day of high temperatures
in the mid to upper 70s. Cloud cover will become more prevalent
late this afternoon and evening across the region as the front
approaches. Southerly winds will begin increasing along the
coast tonight, with gusts up to 25-35 mph through early Monday
morning. Widespread rain associated with this front is expected
to make landfall along the coast around 2-5 AM, slowly moving
inland into the valley by mid to late morning. Model guidance
continues to indicate this front will weaken as it makes
landfall, and rain is mostly expected to dissipate by late
afternoon with only a few scattered showers continuing into the
evening. Latest guidance indicates up to 0.5-0.75 inch of rain
expected along the coast and Coast Range with 0.1-0.25 inch
inland through 5 AM Tuesday.
The next frontal system won`t be far behind. There will be a
brief break in rain for most areas Tuesday morning before the
next, stronger frontal system moves into the region midday
Tuesday through early Wednesday. Southerly winds will be
breezier with this system. Gusts up to 35-45 mph are expected
along the coast, though there could be a few isolated gusts up
to 50 mph as NBM indicates a 15-25% chance of this, mainly late
Tuesday afternoon and evening. Inland areas will mainly see
gusts up to 20-25 mph, though there`s a 25-50% chance of peak
gusts up to 30 mph, mainly when the front passes Thursday night.
Rain will be more widespread with this front, as well, beginning
along the coast midday and pushing inland Tuesday night.
Conditions become more showery Wednesday, with increasing
chances (15-25%) of post-frontal thunderstorms across the entire
area Wednesday late morning into the evening hours. Not
expecting severe thunderstorms, but any that form could produce
heavy rain, gusty winds, and frequent lightning.
Some uncertainty remains on the timing and strength of the next
frontal system, but it will be hot on the heels of the second
one, moving inland sometime late Wednesday into Thursday along
with the parent low that these fronts will be spinning along.
Winds are expected to remain generally elevated Wednesday
through Thursday with gusts up to 35 mph along the coast and 25
mph inland, possibly increasing again briefly as the front
passes. Thunderstorm chances return again on Thursday afternoon
and evening, which similar impacts to Wednesday. Depending on
the timing and track of this last system, showers could continue
into Friday and Saturday, though a number of ensemble members
show dry conditions these days. Ensembles indicate a longwave
trough will begin deepening somewhere over the Western US on
Saturday, but the WPC 500 mb cluster analysis indicates a nearly
50/50 chance of it deepening over the Great Basin area vs over
the Pac NW. If it deepens over the PacNW, rain chances will be
higher. If it deepens over the Great Basin, dry weather will
prevail. Will have to see how the pattern resolves. -HEC
&&
.AVIATION...VFR conditions with high clouds persist tonight across
the Willamette Valley ahead of the next system. High confidence (60-
80% chance) for MVFR/low-end VFR CIGs along the coast tonight as the
next front moves in. Winds will continue generally out of the south
ahead of the front, with gusts of 20-25 kt likely at coastal
terminals through the TAF period. Inland, winds remain under 10 kt.
Rain should begin along the coast around 09-12z Mon and reach the
Willamette Valley by 15-18z Mon. Once the front moves inland, CIGs
within the Valley will fall to low-end VFR with a 20-40% chance for
MVFR CIGs. Widespread rain transitions into post-frontal showers
behind the front by 18-21z Mon along the coast and 21z Mon-00z Tue
inland.
KPDX AND APPROACHES...VFR with high clouds tonight, dropping to low-
end VFR 15-18z Mon as the next front moves through and brings
widespread rain. 15-30% chance for MVFR CIGs 18z Mon-00z Tue.
Southeasterly winds tonight around 6-8 kt turning more southerly
after 15z Tue with the front.        -Alviz
&&
.MARINE...A cold front moving across the waters through tonight
will continue to produce southerly winds of 15-25 kt with gusts up
to 30 kt. Gust of 30-40 kt cannot be ruled out, but are likely to
remain isolated and intermittent. Seas remain at 8-11 ft, levels
hazardous to small craft and meriting continuation of the Small
Craft Advisory across the coastal waters and including the
Columbia River Bar through tonight. After the front moves onshore
Monday morning, winds will ease to 10 kt while seas subside to
6-8 ft by Monday afternoon.
Another, more potent frontal boundary will approach the waters
Monday night into Tuesday before moving onshore by Tuesday night.
There remains high confidence in widespread gales from midday
Tuesday through late Tuesday evening; a Gale Watch also remains in
effect through this period across the waters and including the
Columbia River Bar. Gusts in excess of 40 kt are very likely, a
75-95% chance, while chances of storm-force gusts greater than 48
kt are generally 15-20% or less. These strong winds will also see
seas build to 15-19 ft by Wednesday afternoon, with a 5-25% chance
of 20 ft seas beyond 30 NM.
Southerly winds then steadily weaken below 15 kt by Friday while
seas similarly ease to 4-6 ft by the end of the week. As the
persistent upper low responsible for the repeated frontal passages
finally moves inland next weekend, building surface high pressure
over the northeastern Pacific will see winds return to a seasonable
northerly pattern. -Picard
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Monday for PZZ210-251>253-
     271>273.
Gale Watch from late Monday night through Wednesday morning
     for PZZ210-251>253-271>273.
&&
$$
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NWS PQR Office Area Forecast Discussion