Washington State Forecast Discussion

Western Washington


700
FXUS66 KSEW 051707
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
907 AM PST Sun Jan 5 2025

.UPDATE...Areas of drizzle and lower visibilities continue this
morning with abundant moisture at the surface. Lingering showers
also continue, mainly over the Cascades. Clouds with drizzle will
remain around into the afternoon. Otherwise, no major forecast
updates this morning.

&&

.SYNOPSIS...Light precipitation this morning in the wake of
Saturday's front. A weak system will move by to the south tonight
into Monday morning. Upper level ridge building offshore tonight
will move inland Monday night. The ridge will weaken and shift
east Tuesday. A weakening system will arrive Tuesday night into
Wednesday morning. Another ridge will build Wednesday night into
Thursday then move east Thursday night allowing another front to
arrive Friday.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Satellite imagery shows
front has moved east of the area early this morning. Cloudy skies
behind the front with areas of light showers or drizzle indicated
on the doppler radar. Temperatures at 3 am/11z are in the mid 40s
to lower 50s.

Not much going on weather wise today. Next system headed towards
Northern Oregon will still be offshore by late afternoon.
Precipitation drying up this afternoon with no post frontal cold
air and northwesterly flow aloft. Light flow in the lower levels
combined with a little post frontal lift will keep the light
showers/drizzle going until late morning. Showers continuing in
the Cascades with a couple more inches of new snow. Light flow
continuing into the afternoon hours keeping the low level moisture
in place for a cloudy day. Little change in the temperatures with
highs 5 degrees or less warmer than the current temperatures.

Next system moving inland over Northern Oregon late tonight/early
Monday morning. Chance of rain from about Seattle south beginning later
tonight. Light flow in the lower levels continuing with areas of
fog developing overnight over the northern portions and along the
coast. Lows tonight near 40.

Front well to the southeast Monday morning. Question for the day
is how long will the low clouds and fog last. Upper level ridge
offshore building inland during the day to increase the subsidence
over the area. Northeasterly surface gradients will also help dry
out the low level moisture. Will go with areas of morning fog and
some sunshine in the afternoon. Highs near 50.

Upper level ridge over the area Monday night will move east and
weaken Tuesday. Surface gradients going light again creating a
good environment for fog development overnight for the lowlands.
Could see some dense fog over the Southwest Interior early Tuesday
morning. With the lack of cloud cover lows near freezing in many
places in the interior with all locations at least in the 30s.

Frontal system approaching Tuesday weakening as it runs into what
is left of the ridge. Increasing easterly gradients in the morning
will help erode the morning fog. Increasing middle and high level
clouds in the afternoon. Highs in the mid 40s to near 50.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models trending
a little stronger with the front Tuesday night into Wednesday
morning but the front still falls apart over Western Washington.
Will just have chance pops in the forecast. Instant replay for
Wednesday night and Thursday with another upper level ridge
building over the area. Low level flow light with fog developing
late Wednesday night/Thursday morning. Fog dissipating by Thursday
afternoon. Ridge shifting east Thursday night with a more
organized front arriving Friday. Wet ensemble solutions increasing
with this feature with almost all of the solutions indicating
rain in the lowlands Friday on both the GFS and ECMWF. Models
differ in the strength of the upper level ridge for Saturday. The
GFS has a higher amplitude ridge with only a couple of wet
solutions in the ensembles, ECMWF not as strong with the upper
level ridge allowing an upper level trough moving down the British
Columbia coast to arrive late in the day. Just slight chance pops
in the forecast for Saturday at this point. Felton

&&

.AVIATION...West to northwest flow aloft will turn north to
northeasterly tonight as a weak system passes mostly to the south
of the region and upper ridging begins to build offshore. Post-
frontal shower activity will continue to dissipate this morning.
With plentiful low level moisture in place and light surface
gradients, widespread IFR/LIFR ceilings and visibilities are
expected to persist through late this morning. Conditions will be
slow to improve with ceilings reaching low MVFR thresholds by the
mid-afternoon for most areas.

KSEA...Mostly IFR ceilings expected through the morning with shower
activity coming to an end. Some marginal improvement to low MVFR
expected near or after 21Z. Ceilings are likely to sink back to
IFR at times again tonight. Surface winds southwesterly persisting
at 8-12 kts transitioning to northerly 4-7 knots after around
00Z. 27/14

&&

.MARINE...A weak surface trough and associated front will move into
the Oregon coastal waters tonight with little impact for area
waters. A strengthening surface ridge over the interior of British
Columbia will lead to increasing offshore flow Monday and Tuesday.
Easterlies may occasionally reach small craft advisory criteria near
the west entrance to the strait during that time frame. A
dissipating front is expected to reach the area around midweek with
little impact apart from weakening the strength of offshore flow.
High pressure is then expected to rebuild over area waters before a
front arrives toward the end of the week. All in all, it is expected
to be a rather quiet week for the area with the exception of seas.
Seas over the coastal waters which will occasionally surpass 10 feet
Monday and again midweek. 27

&&

.HYDROLOGY...The Skokomish River is cresting just below flood
stage this morning. The river will begin to recede this
afternoon. Weak systems later this week will not produce
hydrologically significant precipitation.

No river flooding expected in the next 7 days with the exception
of the Skokomish today. JD/Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 10 AM PST this morning for West
Slopes North Cascades and Passes-West Slopes North Central
Cascades and Passes-West Slopes South Central Cascades and
Passes.

PZ...None.
&&