734
FXUS66 KSEW 080304 CCA
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
757 PM PDT Mon Apr 7 2025

.SYNOPSIS...More rain and mountain snow through Tuesday with a
trough over the region. Weak upper level ridge trying to build
over the area Wednesday. The ridge will shift east Wednesday night
into Thursday allowing another front to reach the area Thursday
night. Cool upper level trough over Western Washington Friday and
Saturday with an upper level ridge building Sunday.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Scattered showers
continue across Western Washington this evening as the region
remains under a broad trough that extends from the northeast Pacific
across the Pacific Northwest. The next embedded disturbance plainly
visible on satellite imagery over the Oregon offshore waters will
curl northeastward into the area Tuesday morning for an increase in
showers and isolated thunderstorms. Winter Storm Warnings remain in
effect for portions of the Cascades and this is working out well
thus far with Paradise/Mt Rainier picking up at least 4 inches of
snow since late this afternoon. Current forecasts are on track.
Previous discussion follows with updates to marine and aviation
portions.  27

There is broad troughing over the Pac NW with a parent low spinning
offshore near the Gulf of AK. Across western WA, we`re under moist
S/SW flow with batches of rain moving in and out. The air mass is
slightly unstable and there`s a chance of thunderstorms over the
region too. Snow levels will lower tonight, around 3500-4000 ft, and
the volcanoes may see periods of heavy snow. A Winter Storm Warning
is in effect with heaviest amounts over Mount Baker and Mount
Rainier (up to a foot of snow).

Wet weather continues into Tuesday with more rain and mountain
snow. Showers are enhanced with a passing trough axis due to cross
western WA during the afternoon. Heavy snow is still expected at
Mount Baker, Mount Rainier and White Pass. Snoqualmie will see a
rain/snow mix with around 4-6" at Stevens Pass. By Tuesday night,
we`ll be in post-frontal flow with showers and a convergence zone
aimed at Snohomish and Skagit counties.

A weak ridge will bring drier weather moving into Wednesday. The
air mass will be warmer with temps in the upper 50s to lower 60s.
The ridge holds on going forward to Thursday, keeping part of the
day dry. Rain returns late Thursday afternoon and evening as the
ridge shifts east and a front moves in from the Pacific. 33

.LONG TERM /FRIDAY THROUGH MONDAY/...A trough over the West will
keep rain chances going Friday through the weekend. Temperatures
will be cooler with morning lows in the 30s (beginning Saturday
morning). We`ll see light snow in the mountains as well. High
pressure brings drier weather later Sunday and into early next
week for a break in the weather. 33

&&

.AVIATION...Moist southwesterly flow aloft as upper level troughing
continues to bring showers to western Washington. Mostly VFR
conditions present over W WA, however periods of MVFR to IFR
conditions can emerge under any of the remaining showers this
evening. This on and off shower activity will continue into Tuesday
as the aforementioned upper level troughing moves onshore. Can
expect lower conditions (MVFR/IFR) at times throughout most of the
terminals through the overnight hours due to showers and low level
moisture keeping ceilings low. Surface winds largely south to
southwesterly with majority of terminals seeing speeds generally
within a 10-15 kts range. BLI, CLM and OLM are the exceptions, with
slower speeds ranging 4-8 kts. OLM and BLI should see speeds
increase to join the others by 09Z tonight, but given the southerly
component, CLM may be shadowed keeping speeds there where they are
currently.

KSEA...VFR conditions in place and current radar trends suggest this
might hang on for the remainder of the evening hours. However,
activity upstream suggests current TAF is on track with showers
resuming by 06Z tonight and continuing off and on throughout the
overnight period. This combination of activity coupled with an
already moist air mass in place will allow conditions to erode down
into MVFR through at least 12Z, perhaps longer. To offset that, SW
winds increasing after 12Z may help mixing lift cigs, restoring VFR
conditions early Tuesday morning through the remainder of the TAF
period. South to SW winds expected for the entire period, speeds
generally 10-15 kts, however gusts up to 20-25 kts will be possible
during the afternoon and early evening.

Mazurkiewicz/18

&&

.MARINE...A frontal system moving through the area will
keep winds slightly elevated over the coastal and interior waters. A
small craft advisory remains in effect for the coastal waters for
elevated seas and winds and will go unaltered. A small craft
advisory is also in place for the Central and Eastern Strait for a
push of westerly winds ranging from 15-25 kts, however most obs show
these winds have largely subsided with the exception of Race Rocks
on the Canadian side of the Central Strait. Given both this downward
trend and the persistence of one observation point, will leave this
headline in place until its expiration time of 9 PM this evening.
Another disturbance will push through the waters Tuesday bringing
breezy southerlies across the waters. A brief break in the weather
Wednesday and Thursday before another system approaches the area
near the end of the week.

Combined seas around 9 to 11 feet will generally remain through
Tuesday. Seas look to subside to around 5 to 7 feet by midweek,
before gradually building back up to 10 feet by the end of the week.

Mazurkiewicz/18

&&

.HYDROLOGY...A Flood Watch is effect for the Skokomish River in
Mason County. This is due to the river already running high with
an additional 2 to 2.5 inches of rain along the south slopes of
the Olympics in the next 36 hours. The current forecast has the
river cresting just a few inches below flood stage late Tuesday
night. If the Skokomish River does reach flood stage, it will not
remain over flood stage long with the watch ending Wednesday
morning.

No river flooding on the remainder of the rivers in the next 7
days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning from 5 PM this afternoon to 5 PM PDT
     Tuesday for Cascades of Pierce and Lewis Counties-Cascades
     of Whatcom and Skagit Counties.

     Flood Watch from Tuesday afternoon through Wednesday morning for
     Foothills of the Western and Southern Olympic Peninsula-
     Middle Chehalis River Valley-Olympia and Southern Puget
     Sound-Olympics-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 9 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 11 AM PDT Tuesday 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.

&&

$$