742
FXUS66 KSEW 190433
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
833 PM PST Tue Nov 18 2025

.SYNOPSIS...
Showers give way to mostly dry and clearing conditions tonight.
Cool temperatures Wednesday morning with areas of fog.
Increasing easterly gap winds during the day Wednesday. A weak
front moves in Wednesday night, but splits as it does so, bringing
light precipitation. Additional systems reach the area Friday and
into this weekend, with the potential for more substantial rain
and accumulating snow in the mountain passes Sunday into early
next week. A cooling trend looks to start next week.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
An upper level trough axis has moved east of the Cascades this
evening. Skies have begun to clear across much of the lowlands. But
light surface winds, a long night ahead, and plentiful low level
moisture are expected to result in widespread low cloud development
overnight along with areas of fog by morning. Apart from monitoring
of fog development overnight, current forecasts have trends covered
well. Previous discussion follows with update to aviation portion. 27

Radar imagery and surface analysis show a few very isolated
showers, mostly across the northwest interior. Shower coverage
will decrease tonight as a brief upper level ridge and
associated surface high pressure system moves across the
region. High pressure will quickly move inland tonight. As such,
clouds will clear tonight. This, along with mostly light to
calm winds at least early in the night will allow for areas of
dense fog to develop into early Wednesday morning. The best
chances of seeing fog will be across the Southwest Interior up
through the Kitsap Peninsula and up towards the Seattle metro,
in western Whatcom county, and along the Strait of Juan de Fuca.
Satellite trends will be monitored tonight for the potential
for any advisories. Additionally, low temperatures will likely
drop a decent amount, reaching into the low to mid 30s, to near
40 in the urban metro.

High pressure will remain over eastern Washington/southeastern
British Columbia on Wednesday while a frontal system will
approach the coast Wednesday night. Conditions will be dry
during the day Wednesday. However, winds will begin to increase
early Wednesday morning as offshore gradients increase. Winds
look to peak early Wednesday afternoon. Maximum gusts through
the gaps in the terrain may reach 25-35 mph, with locally up to
40-45 mph near North Bend. Since this is one of the few times
this is expected to peak during the day, a wind advisory will be
issued mainly for the North Bend area.

Rain chances will begin to increase along the coast after around
midnight Thursday, but as the front moves inland, it quickly
begins to split and weaken as upper level support decreases. As
such, rain will devolve rather quickly into scattered showers
for the rest of the area Thursday morning. Precipitation
accumulations will be small to negligible. Showers taper off
Thursday night. Temperatures on Thursday will be a bit warmer,
with highs in the low to mid 50s and lows in the upper 30s to
low 40s.

Along the coast, large long period waves will arrive
Thursday afternoon. However, currently guidance is suggesting
that waves will be just short of high surf advisory criteria.
Will continue to monitor trends as the waves develop and move
into the area. Localized beach erosion and significant run-up
may be possible on Thursday.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Precipitation chances reenter the forecast on Friday for the
far northwest portions of the area as a system tracks across
southern British Columbia. This will try to slowly sink
southward on Saturday before an upper level trough moves into
the area Sunday into Monday, which will bring the best for more
substantial precipitation area-wide. Lowering snow levels will
likely result in some accumulating snow at the passes. There are
still considerable differences in the exact evolution of the
weather this weekend, and the ensembles are still showing about
a 50/50 split between between a cooler and perhaps drier
solution vs warmer and wetter solution. What does look more
likely is next week marking the start of a cooling trend through
the week with highs back in the 40s and lows in the 30s.

62

&&

.AVIATION...
An upper trough axis has moved east of the Cascades with north to
northwest flow aloft developing over Western Washington as a weak
upper ridge builds into the area. Weak surface gradients will become
increasingly offshore during the day on Wednesday. Evening surface
observations show little temperature/dew point separation. With
higher level clouds clearing out, low clouds and fog are already
beginning to form and will become progressively more widespread
overnight into Wednesday morning. IFR or LIFR ceilings with areas of
reduced surface visibility are expected 11Z-16Z for many interior
lowland terminals. Low level offshore flow will begin to develop on
Wednesday and this should help gradually erode the low clouds for a
return to VFR most areas by midday Wednesday.

KSEA...Weak surface winds overnight combined with some clearing and
little temperature/dew point separation lend a good degree of
confidence into the development of low clouds and fog. Satellite
trends and regional observations point toward fog formation as
opposed to stratus. Will incorporate this into the 06Z TAF package.
Fog and low clouds may hang on into late morning before low level
easterly flow breaks through near-surface inversions. Surface winds
light N/NE this evening will become light and variable overnight
then becoming E/NE 5 to 8 knots toward late morning...rising to 10
to 15 knots at times toward 00Z.    27

&&

.MARINE...
Marine conditions look to remain rather tranquil until Wednesday
morning as high pressure moves inland and a frontal system
approaches the coastal waters from the west. Offshore gradients
increase, which will bring Small Craft Advisory winds to the
outer coastal waters as well as through the western Strait of
Juan de Fuca. Winds will ease overnight Wednesday into Thursday
morning as the front moves inland. Additional systems look to
move across the northwest Friday into Saturday with potentially
a stronger system Sunday into Monday, but there remain
significant differences between model outcomes.

Seas around 7 to 9 ft will begin to rise Thursday as a long
period swell group arrives to the west coast. Wave heights will
increase to 16 to 18 ft late Thursday (with a dominant period of
around 15 to 16 s) and will slowly ease to around 10 to 12 ft
Friday and remain around there through the weekend into early
next week.

62

&&

.HYDROLOGY...
No flooding is expected through the week ahead. Stronger
weather systems moving into the region by early next week could
bring periods of heavier rain and will be the next time frame
to watch with respect to hydrologic concerns.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory from 10 AM to 10 PM PST Wednesday for Foothills
     and Valleys of Central King County.

PZ...Small Craft Advisory from 7 AM to 4 PM PST Wednesday for
     Coastal Waters From Cape Flattery To James Island Out 10
     Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 7 AM to 10 PM PST Wednesday 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

&&

$$