Grapeview, Washington Weather Forecast Discussion

352
FXUS66 KSEW 202200
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
300 PM PDT Sat Sep 20 2025
.SYNOPSIS...A frontal system moving through the area late
tonight into Sunday morning will bring widespread rain, breezy
winds, and cooler temperatures. Drier weather will return
Monday and linger through midweek, followed by what looks to be
typical late September weather for the second half of the week.
&&
.SHORT TERM /TODAY THROUGH MONDAY NIGHT/...Mostly clear skies
over the interior with lingering stratus along the coast. Smoke
from fires on the Olympic Peninsula will continue to degrade
air quality through today mainly for areas near the fires and
portions of the interior south of Puget Sound.
Mid level clouds already beginning to move on to the north
coast ahead of an approaching frontal system. Increasing cloud
cover will spread inland through the late afternoon and early
evening with widespread rain on track to move onshore late this
evening and through the interior by early Sunday morning. The
heaviest rain expected along the coast and Olympics from 11pm to
2am and 3am to 6am for the interior lowlands. Showers may stick
around into Sunday morning especially over the Cascades. High
resolution ensembles continue to highlight the formation of a
convergence zone later Sunday morning, keeping precipitation
going over the metro area into the Cascades into Sunday
afternoon. With the trough axis directly overhead by Sunday
afternoon, there may be just enough instability for a lightning
strike or two, but overall the probability is low (10-15%) with
the best bet being with the convergence zone. Precipitation
amounts through Sunday afternoon remain in the ballpark of 0.5
to 1 inch across the mountains and the Pacific coast, with the
interior around 0.25-0.5 inch. More than anything this will
bring a temporary reprieve for the active fires in the area and
help with the air quality. Sunday`s high temperatures will
remain quite cool, in the mid to upper 60s with lows in the 40s
to near 50 in the metro/urban areas going into Monday morning.
Areas of fog can also be expected Monday morning. Building upper
level heights behind the upper level trough will help mostly
clear skies and more seasonable temperatures return Monday
afternoon, with highs a few degrees on either side of 70.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...Upper level ridging looks
to remain in place into Tuesday and Wednesday, allowing for a
gradual warm-up, generally back into the mid to upper 70s with a
few spots at or near 80. Lows remain in the 50s. The pattern
looks to shift around mid-week, opening the door for the
potential for a systems to brush the area late in the week into
the week. This will likely bring more typical late September
temperatures with periods of potential precipitation.
&&
.AVIATION...VFR across all terminals this afternoon and will persist
for the rest of today. As for the coast, conditions are not expected
to improve past MVFR today. Mid to high level clouds will increase
this afternoon in the interior ahead of an approaching cold front.
Ceilings will lower overnight as rain associated with the frontal
system push through Western Washington. Rain is expected to reach
the coastline around 03z-05z and will reach the interior terminals
around 05z-09z. Rain activity associated with the front will start
to gradually subside after 12z-13z for the coast and after 15z-16z
for interior terminals. Some guidance is hinting at a potential
convergence zone developing after 16z-17z in between BFI and PAE.
Improvement into VFR expected early in the afternoon for the
interior terminals. Coastal terminals will likely only improve to
MVFR. Surface winds will get gusty with the frontal passage and
behind the front, with gusts up to 20-25 kt possible.
KSEA...VFR conditions will prevail today. Mid to high level clouds
will increase this afternoon as a frontal system approaches Western
Washington. Latest models have the rain arriving around 08z-09z
Sunday and continuing through around 17z. Ceilings will lower
overnight to MVFR as the rain pushes through the terminal with
improvement into VFR after 20z-21z. Gusty S/SW surface winds of 10-
15 kt will accompany the frontal passage and will continue post-
frontal. Gusts of at least 20 kt are likely starting after 02z.
Probabilities of exceeding 25 kt are around 45%-70% between 12z-18z.
Winds will start to gradually subside Sunday afternoon after 18z.
&&
.MARINE...Latest surface observations near Port Angeles show gusts
are meeting small craft thresholds (which also aligns with model
data), so went ahead and issued the Small Craft Advisory for the
central portion of the Strait of Juan de Fuca a couple hours
earlier.
Surface high pressure will weaken tonight as the frontal system
pushes through area waters tonight through Saturday morning. Winds
will increase across all area waters as the front passes over the
waters, for which Small Craft Advisories have been issued. In
addition, went ahead included the Northern Inland Waters, Admiralty
Inlet, and the western portion of the Strait of Juan de Fuca in the
advisory. A strong push of post-frontal westerlies is expected along
the Strait of Juan de Fuca Sunday morning through the afternoon for
the central and eastern portions. The strongest winds will be in the
central portion, where wind gusts may reach low-end gales. Winds
will gradually subside late Sunday night. In addition, there is a
small chance of thunder (15%-20%) for the coastal waters Saturday
night. Seas will build tonight into Sunday to 8-10 ft for the
coastal waters.
High pressure will build over the waters late on Sunday into Monday
and will weaken slightly as a weakening front moves over the waters
on Tuesday. High pressure will rebuild again over the waters on
Wednesday.
29
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Air Quality Alert until midnight PDT tonight for Foothills and
     Valleys of Thurston and Lewis Counties-Foothills of the
     Western and Southern Olympic Peninsula-Lowlands of Lewis
     and Southern Thurston Counties-Middle Chehalis River
     Valley-Olympia and Southern Puget Sound-Olympics-Southern
     Hood Canal-Willapa and Black Hills.
PZ...Small Craft Advisory from 7 PM this evening to 3 AM PDT Sunday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 1 PM PDT Sunday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.
Small Craft Advisory from 11 PM this evening to 9 AM PDT
     Sunday for Admiralty Inlet-Northern Inland Waters
     Including The San Juan Islands-Puget Sound and Hood Canal.
Small Craft Advisory until 2 AM PDT Sunday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater Out 10 Nm.
&&
$$

NWS sew Office Area Forecast Discussion