Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
821
FXUS66 KSEW 301034
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
231 AM PST Tue Dec 30 2025
.SYNOPSIS...
An upper level ridge will remain in place over Western Washington
through midweek. This will maintain dry conditions and patchy fog. A
more active weather pattern returns on Thursday, with a return of
mountain snow and lowland rain late this week through the start of
next week. An increased threat of coastal flooding due to larger
high tides develops late this week.
&&
.SHORT TERM /TODAY THROUGH THURSDAY/...Latest satellite imagery
shows some scattered high clouds moving over the area, but otherwise
generally clear skies. Although many locations are seeing a 1-3
degree dewpt depression, there are some that are going to 0-1
degrees and as such, fog has developed...mainly over the south Sound
and Chehalis River valley, but also in isolated spots near Arlington
and Port Townsend. Of particular note is a pretty thick band that
has formed along the south shores of the Strait stretching from near
Neah Bay almost reaching Port Angeles. Timing on any fog lifting
should be similar to previous days...most spots should clear out by
late morning while others, especially around Olympia, will likely
hang on until the early afternoon.
Forecast models remain consistent with the upper level ridge holding
court over the Pac NW through at least mid-week, keeping conditions
dry and overnight lows still on the chilly side...residing mainly in
the lower to mid 30s. Some outliers in the SW interior could dip
down into the upper 20s while some spots along the water may stay in
the upper 30s to around 40. Daytime highs will remain in the mid to
upper 40s in the lowlands. As the upper high has been over the area
for some time now...making for a relatively stable atmosphere, the
question of air stagnation concerns does arise. In collaboration
with local air quality agencies, while isolated locations may see
some degradation of air quality, overall there are no widespread
concerns for west of the Cascades at this time.
18
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Overall, model guidance is in good agreement with the next incoming
system moving up into the area Thursday night. While a fair number
/but not quite a majority/ of ensemble members want to sneak in some
precip as early as Thursday afternoon, deterministic models and
majority of ensemble members show chances rising Thursday evening
with those chances rising to high-end Chance to Likely during the
overnight hours and staying that way into Friday. A more organized
system moves in quickly Friday afternoon as an upper level trough
sinks southward over the eastern Pacific and churning moisture up
into the area. As has been stated in prior discussions, this follow-
up system continues to show some atmospheric river-like qualities,
yet models remain on track keeping the bulk of this moisture well to
the south of WA...targeting northern CA instead. This trough will
slowly rotate northeastward, keeping precip going into Saturday.
Just as this feature exits Saturday evening, yet another trough dips
in behind it, spinning additional moisture up into the area to keep
rain in the forecast for the remainder of the weekend. Deterministic
and ensemble model data starts to hint at the potential for a small
break in the action Sunday evening...maybe stretching into Monday
morning...as a weak shortwave ridge tries to exert some influence
over the area...but by Monday evening, the trough responsible for
Sunday`s precip begins to work toward the coast brining yet more
rain.
Daytime highs in the long term remain fairly steady, mainly in the
mid to upper 40s, although some isolated spots could reach 50 at
times. It is the overnight lows that get a much needed boost, in the
upper 30s to lower 40s.
Finally, the threat of minor coastal flooding will continue to
increase late in the week. While there is uncertainty regarding the
timing and strength of the upcoming weather systems, they could
exacerbate coastal flooding concerns.
18
&&
.AVIATION...
Mostly VFR early this morning with passing high clouds and localized
IFR/LIFR in fog and low stratus across the Chehalis Basin south of
the Puget Sound. Fog/freezing fog and stratus are expected to expand
through the morning for areas west and south of the Sound, with
terminals east of the Sound expected to remain VFR as northeast
winds persist. A slight improvement in conditions is possible by the
late afternoon hours for terminals seeing fog early this morning,
however expect improvement to be short-lived with fog and low
stratus on track to redevelop once again tonight. Surface winds will
generally remain out of the north to northeast around 4 to 8 kt this
morning, gradually transitioning back to southerly by late this
afternoon.
KSEA...VFR conditions expected to prevail through the period with NE
winds around 4-8 kt early this morning. While a few low clouds will
be possible within the vicinity of the terminal this morning,
northeasterly winds will likely help limit fog potential and keep
VFR conditions prevalent at the terminal. Winds will gradually
transition to more southerly throughout the afternoon today.
15
&&
.MARINE...
High pressure will remain situated over the coastal waters through
Wednesday, while a weak thermal trough remains situated along the
coast today. This will continue to promote offshore flow through the
first half of the week. Seas will continue to hover between 6-9 feet
today with a west-northwest swell moving into the coastal waters.
Seas will then gradually subside towards 5-7 feet by midweek.
Dense fog may develop over portions of the interior waters with
clearing conditions and light winds during the overnight periods the
next few days and may restrict visibilities across the waters at
times.
A more active pattern returns the second half of the week, with the
next frontal system expected to move into the area waters on
Thursday, followed by a stronger system on Saturday. Increasing
winds and seas building to 10-13 feet by the weekend will likely
bring the next round of area-wide headlines.
14
&&
.HYDROLOGY...
No river flooding is expected during the next seven days.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&
$$
NWS SEW Office Area Forecast Discussion