963
FXUS66 KSEW 082246
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
346 PM PDT Tue Jul 8 2025

.SYNOPSIS...High pressure shifting east tonight. Weather system
moving down the British Columbia coast going through Western
Washington Wednesday bring rain to portions of the area along with
much cooler temperatures. Post frontal convergence zone over
Snohomish County Wednesday night. Upper level ridge rebuilding
Thursday with the ridge remaining over the area into the first
part of next week.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Satellite imagery shows
front moving down British Columbia coast over Northern Vancouver
Island this afternoon. Clear skies over most of Western Washington
with high clouds over the North Coast. Temperatures at 3 pm/22z
were in the mid 70s to mid 80s over the interior and in the 60s
along the coast.

Front will continue to move slowly southeast tonight but still be
northwest of the area come sunrise Wednesday morning. Increasing
clouds over the area with rain developing along the North Coast
and a chance of rain over the Northwest Interior. The increasing
clouds will keep lows in the mid 50s to lower 60s.

Front slowly moving through Western Washington Wednesday with the
frontal passage in the afternoon. West northwesterly flow aloft
will rain shadow the Central Puget Sound with just a chance of
rain south of Seattle over the interior. Rain along the coast and
over the Northwest Interior. Rainfall amounts significant for this
time of year over the Northwest Interior and Coast with a quarter
of an inch or so. Even more in the North Cascades with a quarter
to a half inch with isolated pockets up to an inch. For the
remainder of the area a tenth of an inch or less. High
temperatures will be up to 20 degrees cooler with 60s common.

Post frontal convergence zone between Seattle and Everett
Wednesday night with a tenth to a quarter inch more of rain in
the Central Cascades and foothills. Drying trend behind the front
for lowland locations outside of the convergence zone. The zone
will dissipate after midnight. Under mostly cloudy skies lows in
the 50s.

Upper level ridge beginning to rebuild over the area Thursday with
the ridge building continuing Thursday night into Friday. 500 mb
heights in the low 580 dms Thursday morning pushing 590 dms by 00z
Saturday. Onshore surface gradients continuing through Friday with
the onshore flow becoming northwesterly beginning Thursday night.
Clouds lingering Thursday morning will dissipate by Thursday
afternoon leaving mostly clear skies for Thursday night into
Friday. Highs in the mid 60s to mid 70s Thursday warming into the
70s to mid 80s Friday. Lows in the upper 40s and 50s.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Upper level ridge
remaining in place through the extended period with weak low level
northwesterly onshore flow. This will keep highs from getting too
warm over the weekend, 70s to mid 80s over the interior and near
70 on the coast. Weak shortwave moving over the top will dent the
ridge Sunday night into Monday. No precipitation with this
feature. Low level onshore flow increasing behind the shortwave
cooling high temperatures on Monday a couple of degrees. Ridge
begins to rebuild Tuesday warming highs back into the 70s to mid
80s. Models hinting at offshore flow developing mid week warming
temperatures even more. Felton

&&

.AVIATION...Widespread VFR conditions across the terminals this
afternoon and will persist into the evening. A weak front will bring
increased cloud cover tonight, with ceilings expected to lower into
MVFR for the interior terminals. IFR conditions are also possible
for the interior terminals, with a 20%-40% along the Kitsap
Peninsula, Strait, and KPAE. IFR conditions expected along the
coast, including reduced visibility, with the potential for ceilings
to decrease to LIFR (40-60%). Showers expected to start impacting
the terminals early Wednesday morning. Improvement into VFR is not
expected with this TAF package at this time, as the latest guidance
keeps the ceilings lowered well beyond the TAF package.

Generally southwesterly winds at most terminals. Northerly flow
along KPAE will attempt to push down south. Winds may turn
northwesterly at KBFI this afternoon, however they are not expected
to make it further south. Breezy conditions along the Strait of Juan
de Fuca expected this afternoon. Surface winds will become more
southerly overnight. Winds speeds will increase Wednesday morning to
8-13 kt, with gusts up to 20 kt possible.

KSEA...VFR conditions will prevail into the evening hours. Low
clouds will push into the terminal, lowering ceilings to MVFR and
will prevail throughout the remainder of the TAF package. Guidance
hints at the potential for IFR ceilings between 10z-18z, with a 25%-
35% chance. Northerly surface winds to the north of the terminal are
not expected to impact the terminal this afternoon, rather winds
will turn more westerly-southwesterly. Winds will shift more
southerly overnight and will increase Wednesday morning to speeds of
10-13 kt, gusting up to 20 kt.

&&

.MARINE...Another push of westerlies across the Strait of Juan de
Fuca is expected this afternoon, with a Small Craft Advisory in
effect until Wednesday morning. Another round of westerlies is
expected Wednesday afternoon, which may require additional
headlines. A weak trough will move over the waters Wednesday morning
and strong high pressure will rebuild over the area waters Wednesday
afternoon into late in the week. High pressure will weaken slightly
over the weekend, but will remain the dominant feature over the
waters into early next week, keeping northwesterly flow over the
coastal waters. Seas generally  3-5 ft throughout the week,
increasing over the weekend to 5-7 ft. Guidance is hinting at the
potential for steep seas over the weekend.

29

&&

.FIRE WEATHER...Warm and dry conditions with RHs in the 20s to
30s this afternoon along with some breezy conditions with gusts
locally up to 20 to 25 mph are contributing to elevated fire
weather conditions. Luckily, a frontal system just offshore will
move across the tomorrow, allowing for a return to cooler and more
moist conditions with some light precipitation expected. Wetting
rains are possible across portions of the northern Cascades.

Upper ridging will then build back into Western Washington late
Thursday, resulting in the return of warm, dry weather and elevated
fire weather conditions on Friday. This will be the driest day of
the period, with RH values dropping back into the 25% to 35% range
over the mountains and across the lowlands south of the Puget Sound.
Warm and dry conditions look to persist into next week but the
details remain uncertain at this point to the degree of onshore flow
going into next week.

62/15

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 10 PM PDT this evening for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

&&

$$