210
FXUS66 KSEW 110330
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
830 PM PDT Thu Apr 10 2025

.UPDATE...Post-frontal showers continue this evening, with
convergence zone activity associated with a NE to SW oriented band
of showers Whidbey Island northwards. Showers will continue
tonight, primarily for the Olympic Peninsula and north of King
County. No major forecast updates this evening.

&&

.SYNOPSIS...Isolated post-frontal showers through Friday with a few
additional showers on Saturday. Conditions will dry out starting
on Sunday with high pressure building over the area and persisting
into late next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Radar imagery shows rain
moving across Western Washington as a cold front continues to push
inland this afternoon. The latest observations show gusty winds
already impacting the region. Winds will begin to ease late this
evening into tonight. The strongest winds will be along the coast
and the northern interior, where gusts above 40 mph are likely.
Isolated gusts exceeding 45 mph (40-50% chance) are possible along
the coast and northern interior. In addition, SBCAPE values
80-100 J/kg may promote the development of some thunder this
afternoon. There is a 15-20% chance of thunder for the northern
Cascade foothills and locations north of Everett. Everywhere else,
has around a 10% chance. The lowlands will see around 0.10-0.20
inches of rain, with higher localized amounts in the Cascade and
Olympics (0.40-0.80 inches). Behind the cold front, scattered showers
will remain possible. The latest model runs hint at convergence
zone developing north of I-90 late this evening into tonight.

Snow levels will hover around 5000-6000 ft this afternoon at the
passes. Therefore, any snow accumulations with this system will be
limited to the higher elevations. Snow levels will decrease late
tonight into Friday down to 3000-3500 ft, and by Saturday they
will decrease to around 2500-3000 ft. A trough lingering over the
area will keep showers in the forecast on Friday and Saturday.
This system will bring lowland rain and mountain snow. Snow
accumulations in the passes will will be light (1.00-3.00 inches),
and rain accumulations across the lowlands will be 0.10 inches or
less.

An upper level ridge will build offshore on Saturday. It will move
onshore on Sunday and dry out the region. High temperatures will
generally be in the 50s through the weekend, with each day
gradually becoming warmer. By Sunday, some locations may see highs
in the low 60s. Low temperatures will become colder into the
weekend; temperatures will be in the low 40s on Friday. By
Saturday and Sunday, low temperatures will be in the 30s to low
40s, with colder temperatures across the southern interior (low-
to-mid 30s). The combination of mostly clear skies and light
winds overnight may promote the development of patchy frost across
the southern interior.

.LONG TERM /TUESDAY THROUGH FRIDAY/...There is general agreement
between long-term ensemble guidance that an upper level ridge will
persist into Monday. The ridge will weaken on Tuesday as a
shortwave through pushes through the region. Current model
guidance shows that precipitation will be limited to British
Columbia and northern Cascades. Upper level ridging will rebuild
over the Pacific Northwest on Wednesday and Thursday. There is
some disagreement in the ridge axis location and strength among
ensemble models; however, a general upper level ridging pattern is
favored.

High temperatures on Monday will be in the low to mid 60s.
Temperatures will slightly decrease on Tuesday to the 50s to low
60s and will remain through Thursday. Low temperatures will
generally be in the low-to-mid 40s.

&&

.AVIATION...Southwesterly flow aloft as an upper level trough and
associated front move out of W WA. Surface winds predominantly south
to southwest with speeds varying greatly over the area. Most
terminals currently seeing speeds ranging 10-15 kts with some
occasional gusts to 25 kts still out there. BFI, BLI and CLM have
already seen winds ease to 5-10 kts, where majority of terminals
should end up between 04-06Z tonight. PAE, on the other hand, seeing
some pretty strong winds as of 02Z with speeds running 25-30 kts and
gusts up to 45 kts. These are expected to ease by 04-05Z to fall in
line with the above mentioned majority of stations.

Mix of VFR to MVFR cigs out there this evening, with locations under
showers more prone to the lower conditions. Widespread VFR
conditions...albeit low-end VFR...expected to emerge tonight and for
the remainder of the TAF period as a ridge starts to build into the
area. Locations more prone to lower cigs such as OLM, PWT and HQM
could see cigs dip down into MVFR, but at this time there is no
expectation for IFR conditions nor any significant vis reductions.
Cigs could see some improvement late friday morning and into the
afternoon...although most terminals will remain within a 3000-5000
ceiling.

KSEA...Lingering MVFR conditions this evening should lift back into
low-end VFR by 07Z tonight. Southwesterly winds still breezy this
evening ranging 10-15 kts with gusts up to 25 kts. This, much like
the cigs, should ease off by 07Z, falling into speeds ranging 5-10
kts. Probabilistic guidance still hinting at a 25-35 percent chance
of MVFR cigs developing at the terminal again by early Friday with
potential for convergence zone showers to drift south after flow
turns northerly by 18z Fri. Not much confidence in the former, so
will likely not be included in 06Z issuance, but will need to
consider PSCZ development...maybe going for some VCSH Friday
afternoon.

18

&&

.MARINE...A frontal system will exit the area tonight, allowing
winds to gradually ease. Winds have already come down over the
coastal waters, so have cancelled Gale Warning. Did have to replace
it with an SCA for seas for the outer coastal waters, as seas there
still ranging 8 to 10 ft. SCAs remain in effect for the interior
waters from the Puget Sound waters up to the Canadian border, as
winds continue to hang on there. A push of westerly winds down the
Strait of Juan de Fuca will also yield small craft westerlies in the
wake of the front into Friday morning. Winds will then ease on
Friday as high pressure starts to build back over the northeastern
Pacific.

High pressure will persist over the coastal waters through the
weekend. Guidance then hints at a trough extending northward along
the Washington coast by early Monday. Should this come to fruition,
this would allow for winds to briefly turn offshore on Monday.
Offshore winds will be short-lived, however, as high pressure over
the northeastern Pacific builds back over the coastal waters by
Monday evening. A frontal system may clip the waters early next
week as it moves inland to the north, but does not look to bring
much impact to the area at this time.

As stated earlier, outer coastal waters will see seas 8-10 ft at
least into Friday afternoon before easing while inner coastal waters
will linger around 6-8 ft. Seas will subside towards 4-6 ft again
over the weekend and hover between this range into early next week.

15/18

&&

.HYDROLOGY...No river flooding is expected over the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Friday 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 PM PDT this evening for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands-
     Puget Sound and Hood Canal.

     Small Craft Advisory until 2 PM PDT Friday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

&&

$$