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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 142209
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
305 PM PDT Sun Apr 14 2024

.SYNOPSIS...Weak high pressure overhead today before upper-
level troughing returns on Monday bringing cooler temps and showers
back to western Washington. Ridging will return later this week with
the potential for more warm and dry weather.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
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Current satellite imagery
shows most of the stratus present over the coast has pushed back to
the Pacific waters...although some scattered low to mid level clouds
linger. The remainder of W WA remains under mostly clear skies with
perhaps a stray cirrus here and there.

Upper level ridging in place is likely to keep things that way for
much of the day today before clouds associated with the incoming
frontal system start to work their way into the area tonight. Timing
still remains a little fuzzy as deterministic models continue to
waffle on timing...the GFS favoring a later frontal entry than the
ECMWF. Neither model seems to be particularly impressed with precip
amounts, each one showing the system to be far weaker than in
previous runs. Ensembles tending to agree with these current
reduction in expected precip amounts and both deterministic and
ensemble data all seeming to agree on letting the chances for precip
linger throughout much of Tuesday...with ensemble QPF guidance even
showing a bit of a bimodal split as opposed to grouping precip all
together as in previous runs. Ultimately, current forecast tries to
straddle the line of incorporating the new data into the old
trend...and this appears to be the best way to go for now...keeping
the earlier starting time with the front making it to the coast at
or around 12Z Monday morning, then allowing PoPs to linger
throughout much of Tuesday with highest chances during the event
still remaining over the Cascades. Wednesday sees upper level
ridging return to the area with generally dry conditions. ECMWF and
ensembles on the same page, keeping the entire CWA dry, however the
GFS wants to keep some moisture present over the central Cascades.
Unfortunately, the NBM seems to have latched onto this as well,
injecting some slight chance PoPs where meteorologically there
really should not be any...but given that the range is 10-20 pct,
ultimately there really is not much of a difference.

Temps today still expected to be split with mid to upper 50s
expected along the coast and water adjacent locations while the
interior will top out in the mid to upper 60s. Monday and Tuesday
will see temps more uniform throughout the area as well as cooler,
with highs in the lower to mid 50s. Wednesday kick starts a new
warming trend in earnest with highs for much of the lowlands ranging
in the upper 50s to lower 60s.

18

.LONG TERM /THURSDAY THROUGH SUNDAY/...Dry conditions with warming
temperatures will remain the case for the bulk of the long term
forecast as upper level ridging will continue to be the dominant
weather feature. Deterministic models disagree on extent and
intensity and the GFS seems to insert a retrograding trough for
reasons that elude current reasoning. Ensembles definitely in
agreement for a prolonged dry stretch. Next system progged to enter
the area possibly Saturday morning or afternoon. Deterministic
models disagree and this disagreement has the trough either passing
to the south as a closed low with precip barely nicking the SW
corner of the CWA via the GFS or a weakening trough that fizzles out
while crossing according to the ECMWF. Ensembles have a wide range
of solutions, however the ensemble mean still suggests that both
Saturday and Sunday could see some, albeit minimal, precip. NBM
PoPs in the forecast remain in the Slight Chance to low-end Chance
range /10-30ish pct/...splitting the difference yet still conveying
low confidence...which would be the proper attitude toward the end
of the forecast period.

Daytime highs will continue to warm Thursday and Friday, the former
in the lower to mid 60s and the latter in the mid 60s to around 70.
Precip or no...the next system will bring temps down somewhat, with
highs both Saturday and Sunday in the upper 50s to mid 60s.

18
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&&

.AVIATION...
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Westerly flow aloft as a cold front and upper low dig
southward into Western Washington into tonight. Onshore flow
continues at the surface with convergence over the Seattle metro
across central King County with northwest wind at BFI and a
transition to southwest now occuring at SEA. Expect southwest winds
to overtake and spread across most of the Puget Sound terminals this
afternoon and evening before a cold front begins diving southward
across the area. Mostly VFR conditions across the terminals this
afternoon, with the exception being HQM, where stratus is still
holding tight this afternoon. A brief break is forecast here from
around the 22-06Z timeframe before stratus moves back onshore. CIGs
will lower tonight, with a 30% chance for MVFR CIGs by around 09Z
through 20Z. Scattered light rain showers and drizzle likely much of
the day Monday across the Puget Sound terminals, though VSBY
restrictions look minimal.

KSEA...VFR cigs with high clouds building through the remainder of
the day. Light and variable winds will shift to the southwest then
nearly due south ahead of a cold front that will dig southward
across Western Washington tonight. CIGs lower closer to MVFR
thresholds after 09Z with a 25% chance of MVFR or lower through 20Z
as CIGS lift back to 4000-5000 foot range. Light rain and showers
expected with weak convergence banding through much of the day after
10-12Z. Surface winds should stay out of the southwest through the
day Monday from 8 to 12 kt.

Davis
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&&

.MARINE...
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Diffuse high pressure is retreating to our south this
afternoon as a cold front dives south across British Columbia,
poised to cross the area waters late tonight into Monday morning.
Onshore flow continues, with Small Craft Advisories extended through
11 AM across the coastal waters and West Entrance to the Strait of
Juan de Fuca. A strong push down the Strait is beginning with gusts
now reaching 25 kt at Race Rocks across the international border.
Gale Warning continue for the Central and East Strait, though they
have been trimmed back to expire at 3 AM. Wind gusts to 35 kt are
likely. Winds will ease through the morning with Gales likely being
dropped to Small Craft Advisories before they quickly pick up again
Monday afternoon. A Gale Watch has been issued for the Central and
East Strait along with Admiralty Inlet Monday afternoon through
early Monday night, with Gales likely (over 80% confidence).
Marginal chances (50% or less) for brief SCA-level wind gusts Monday
night through much of Tuesday over the offshore waters.

Seas from 6 to 8 feet will increase closer to 10 feet tonight over
the coastal waters before gradually lower back to 7 to 9 feet
through the day Monday. Seas continue to lower through the week,
trending below 5 feet Thursday and Friday.

Davis
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&&

.HYDROLOGY...No river flooding is expected through the next seven
days.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...Small Craft Advisory until 11 AM PDT Monday 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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Gale Warning until 3 AM PDT Monday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Gale Watch from Monday afternoon through late Monday night for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 3 AM PDT Monday for Admiralty Inlet.

     Gale Watch from Monday afternoon through late Monday night for
     Admiralty Inlet.
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&&

$$