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279
FXUS66 KSEW 251030
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT Thu Jul 25 2024

.SYNOPSIS...
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Upper level trough moving off to the northeast today.
Weaker upper level trough moving over the area for the weekend. A
frontal system will move inland mostly over British Columbia
Monday with the southern end of the front moving through Western
Washington. Upper level trough axis moving through Tuesday with a
weak upper level ridge beginning to build Wednesday.
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&&

.SHORT TERM /TODAY THROUGH SATURDAY/...
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Satellite imagery shows
mostly cloudy skies over most of Western Washington early this
morning. Doppler radar has light showers over the North Cascades
and in a convergence zone from Central Snohomish county westward
to just south of Port Townsend. Temperatures at 3 am/10z were in
the mid 50s to lower 60s.

Convergence zone over mostly Snohomish county will begin
dissipating later this morning. Weak shortwave associated with the
upper level low over Central British Columbia slowly moving
northeast of the North Cascades this morning. Both of these
features will produce isolated showers this morning. For the
remainder of the area mostly cloudy skies. Cloud cover decreasing
across the area this afternoon. With the cloud cover and cooler
temperatures aloft highs today will be a little below normal, in
the mid 60s to mid 70s.

Upper level trough east of the area tonight with a weaker trough
beginning to form offshore. Low level onshore flow will become
light. This will prevent the marine layer from getting much into
the interior. With the lack of cloud cover the cooler locations in
the interior will drop into the upper 40s overnight. Lows for the
remainder of the area in the lower to mid 50s.

Weak upper level trough developing over Western Washington late
Friday. Not much with this feature with mostly sunny skies for
all but the coast. Shallow marine layer bringing some low clouds
to the coast in the morning. The clouds will retreat offshore by
afternoon. Highs near normal with 70s and lower 80s interior and
mid 60s to lower 70s coast.

Weak trough remaining over Western Washington Friday night and
Saturday. Increasing onshore gradients Friday night will pull the
marine layer into the interior but at this point the onshore flow
does not look strong enough to get the marine layer east of Puget
Sound Saturday morning. The stratus will retreat to the coastline
by midday. Lows FRiday night mostly in the lower to mid 50s.
Highs Saturday in the 70s in the interior and mid to upper 60s
coast.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Extended models in pretty
good agreement with the weak upper level trough over the area
Sunday followed by a rare late July frontal system Monday into
early Tuesday. Main portion of the front moving into British
Columbia with Western Washington getting the southern end of the
front. With 500 mb heights in the mid to upper 570 dms plus
Western Washington on the southern end of the front plus the
climatology for this time of the year will keep pops in the chance
category for Monday and Tuesday. July 29th is the driest day of
the year in Seattle. In 79 years of records at seattle- Tacoma
airport it has only rained a total of 0.31 inches on July 29th (
0.17 inches in 1993, 0.11 in 2008, 0.02 in 1955 and 0.01 inches in
1981 ). Upper level trough axis moving through later Tuesday. Highs
in the mid 60s to mid 70s with lows mostly in the 50s.

Weak upper level ridge building Tuesday night and Wednesday for
dry and warmer weather. Lows Tuesday night in the mid 50s to lower
60s. Highs Wednesday near normal, 70s and lower 80s inland and mid
60s to lower 70s coast. Felton
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&&

.AVIATION...
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An upper level low will continue to fill as it moves
inland over southern British Columbia Thursday. This will swing
around a jet max over the state with strong west flow aloft
(particularly at higher altitudes over 30,000 feet with 100 kt
winds). Continue to see wind gusts in terminals outside the Strait
of Juan de Fuca with the strong marine push (KBLI gusted to 15 kt,
and 20 kt were observed Oak Harbor and KCLM). Once the low moves
inland, winds around the strait will decrease to west at 8 to 12 kt
(with gusts to 16-18 kt periodic throughout the day). Remaining
inland areas will see southwest winds 6 to 10 kt (couple gusts to 15
kt possible) turning northwest late this afternoon.

Overcast skies are currently present - currently VFR but expected to
drop to MVFR this morning in several areas (highest confidence along
the coast, Cascades/Olympics, and north of Everett to the Canadian
border). Pockets of IFR are possible in the mountains (low CIGs and
VIS). Once the low moves out, majority of CIGs will scatter out late
this morning and afternoon (some may remain along the coast at a VFR
level).

KSEA...VFR/overcast CIGs currently overhead. NBM gives a 20% chance
of MVFR ceilings (between 12 and 18Z this morning) but deterministic
guidance estimates CIGs around 3,000 to 4,500 feet. All CIGs are
expected to scatter out by 20Z. Winds will rotate from east to
southwest this morning, becoming northwest late Thursday afternoon
at 6 to 10 kt (a gust or two to 15 kt possible).

HPR
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&&

.MARINE...
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A strong upper level low will fill moving inland this
morning. High pressure remains out in the east central Pacific Ocean
with ridging up to Alaska. This will continue onshore flow with west
winds in the Strait of Juan de Fuca, and northwest winds in the
coastal waters. The associated jet max with the low has been able to
mix strong winds down to the Strait of Juan de Fuca (observed wind
gusts to 35 kt at Smith island this morning). With the push
gradually weakening this morning, the gale threat will end, but
there remains a strong chance (based on HREF ensemble guidance) for
frequent gusts to 25 kt in the Central/East Strait of Juan de Fuca
throughout the day. A small craft advisory will replace the gale
warning from 5 AM to 11 PM Thursday. Winds will drop off in the
advisory area late tonight.

The outer coastal waters may see northwest winds up to 20 kt and
gusts to 25 kt Friday evening/Saturday. Otherwise winds remain light
at 8 to 14 kt for remaining areas. Wave heights will hold at 3 to 6
feet through next week.

HPR
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...None.
PZ...Gale Warning until 5 AM PDT early this morning 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 Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT early this morning for
     Admiralty Inlet.
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&&

$$