Heisson, Washington Weather Forecast Discussion

686
FXUS66 KPQR 272120
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
220 PM PDT Sat Sep 27 2025
.SYNOPSIS...Dry and mild through Sunday before conditions 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...Saturday Afternoon through Friday...Dry and mild
weather continues this afternoon through Sunday with inland high
temperatures in the 70s. A significant pattern change is in
store for the PacNW starting Monday as a series of frontal
systems associated with an upper level parent low pressure
system will bring periods of widespread rain through the work
week. Expect increasing clouds throughout the day on Sunday as
well as winds shifting southerly and increasing slightly as the
first frontal system approaches the coast. Some breezy southerly
winds are expected along the coast ahead of and along front,
mainly gusts up to 25-35 kts from around 3 PM Sunday through 5
AM Monday. Latest guidance continues to slow down the approach
of this front as satellite imagery shows it slowing over the
Eastern Pacific. Most guidance now does not have precipitation
beginning to impact the coast until early Monday morning around
2-5 AM and then pushing inland into the valley over the next few
hours. This will be a relatively quick- hitting system with
stratiform rain turning to scattered showers by the afternoon.
Rain amounts with this system are diminishing a bit in latest
guidance, especially as the valley seems like it might have a
bit of a rain shadow. Latest forecast suggests 0.5-0.8 inch
along the Coast and Coast Range, 0.25-0.5 inch along the
Cascades, and 0.2-0.45 for inland valleys.
The next frontal system is still slated to be stronger than the
first, impacting the region Tuesday into Wednesday. Winds could
be more impactful with this front, especially along the coast.
NBM indicates anywhere from a 25-50% chance of wind gusts
reaching at least 50 mph along the coast within a 24 hour period
ending 11 PM Tuesday. However, significant spread exists within
GFS, Euro, and Canadian ensemble members on strength of the
winds with a more likely scenario being widespread gusts up to
35-45 mph with maybe a few isolated gusts higher. Some timing
uncertainties continue, as well, but generally expect winds to
increase along the coast Tuesday afternoon through Wednesday
morning, peaking late Tuesday afternoon through the evening.
Winds inland don`t look strong at this point with only a 5-10%
chance of gusts reaching 40 mph in the valley. Best chances are
for gusts up to 25 mph, locally up to 30 mph as the front
passes. Another widespread band of rain will move through the
area Tuesday afternoon/evening through early Wednesday, with
showers continuing through the day Wednesday as well as an
increasing chance (15-25%) of post-frontal thunderstorms in the
afternoon. Rain amounts are expected to be higher with this
system than the first one. There`s an 75-95% chance of at least
1 inch of rain along the coast, Coast Range, and Cascades
between 5 AM Tuesday and 5 AM Thursday. There are similar
probabilities for 0.5 inch of rain for inland valleys with
probabilities decreasing to 50-65% for 0.75 inch of rain.
For Thursday into Friday, ensemble guidance is in good
agreement that the unsettled pattern will continue. However,
uncertainty increases in specific details. The parent low
pressure system is finally slated to move onshore sometime
Thursday into Friday, though there`s quite a bit of spread in
the ensemble members on how much rain is expected with this.
Latest NBM mean along with ensemble means suggest another
0.5-0.75 inch along the coast with 0.25-0.5 in for inland
valleys. Keep an eye out for updates! -HEC
&&
.AVIATION...High pressure is receding ahead of a weak frontal
system approaching from the Northeast Pacific. VFR conditions will
continue through this afternoon, before low marine stratus at
around 500 ft will bring IFR/LIFR cigs and IFR vis to coastal
terminals by 00-03z Sun. Inland, there are low to moderate
chances, around 30%, of MVFR or lower cigs from 12-18z Sun if
marine stratus can push far enough east. Light north to northwest
winds this afternoon will turn out of the south this evening and
overnight ahead of the approaching front. Rain is likely to hold
off until after 18z Sun.
KPDX AND APPROACHES...Continuing VFR conditions beneath sct-bkn
high clouds through much of the period. A marine push overnight
may see low stratus reach up the Lower Columbia, with a 30-40%
chance of cigs at 1-2 kft or lower. Light northwest winds today
will turn out of the south overnight. -Picard
&&
.MARINE...Surface high pressure continues to weaken as a cold
front steadily approaches the coast from the northwest. Winds
remain out of the north to northwest at 5-10 kt into tonight as
seas fall from 8-10 ft to 6-8 ft by midday Sunday as northwest
swell eases. Local buoy observations additionally support Small
Craft Advisories remaining in effect across the waters, including
the Columbia River Bar, through this evening before seas fall
below hazardous thresholds.
Winds will turn out of the south overnight tonight ahead of the
approaching frontal boundary, and then build to 20-25 kt with
gusts to 30-35 kt by Sunday night. Mid-range, relatively coarse
guidance continues to support a roughly 30% chance of gale-force
gusts Sunday night into Monday morning, while the latest high-
resolution ensemble guidance suggests much higher chances of 80%
or more. At this lead time, have opted to hold off any issuance of
Gale Watches given this substantial and sudden disagreement,
however actual chances of gales may be higher than previously
advertised. As southerly winds build, seas will follow, rising to
9-12 ft by Sunday night, before falling to 6-8 ft through Monday
as winds subside.
Another, more potent frontal boundary will move into the waters
Tuesday into Tuesday night. There is high confidence in widespread
Gales across the waters, with 75-95% chances of gusts of 40 mph
or higher. Chances of storm-force gusts of 55 mph or higher also
remain elevated, 25-45% across the waters. Driven by strengthening
winds, seas will quickly build to around 15 ft, with a continued
10-20% chance of reaching 20 ft, especially beyond 30 NM. Seas
look to slowly subside, but remain above 10 ft into the latter
part of next week. -Picard
&&
.BEACH HAZARDS...A low pressure system over the northeast Pacific
is sending a fresh northwest swell of 7-10 ft with a dominant
period of 14-16 seconds into OR and WA coastal waters. This is
producing an elevated sneaker wave threat through this evening.
Waves can run up significantly farther on a beach than normal,
including over rocks and jetties. Sneaker waves can suddenly knock
people off of their feet and quickly pull them into the frigid
ocean which may lead to serious injury or drowning. /42
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210-
     251>253-271>273.
&&
$$
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NWS PQR Office Area Forecast Discussion