415
FXUS66 KSEW 252249
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
349 PM PDT Fri Jul 25 2025

.SYNOPSIS...Zonal flow will continue into Saturday, maintaining
cooler and cloudy conditions across western Washington. Southwest
flow aloft will begin to develop on Sunday, kicking off a warming
and drying trend with chances for thunderstorms towards the middle
of next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...With low pressure to the
north and high pressure to the south, zonal flow aloft will
continue to bring moist onshore flow to western Washington through
Saturday. High temperatures will be limited by the cloud cover
this afternoon, reaching the upper 60s to near 70 and the upper
50s to near 60 along the coast. The weak trough over British
Columbia will shift further inland on Saturday, bringing a repeat
of cooler and cloudy conditions to western Washington. However,
slightly less cloud cover on Saturday afternoon may allow
temperatures to peak a degree or two warmer than today.

A warming trend will begin on Sunday as a high pressure ridge
begins to build over the south central US and a low pressure
system deepens over the Gulf of Alaska. While conditions will stay
dry through Monday, flow aloft will turn southwesterly and allow
temperatures to warm up several degrees. Highs will return to near
seasonal averages on Sunday and Monday with plentiful afternoon
sunshine.

.LONG TERM /TUESDAY THROUGH FRIDAY/...A deep upper level low will
churn offshore through the extended period, generating southerly
flow aloft over western Washington and injecting periods of
moisture northward. Ripples in the southerly flow may generate
thunderstorms throughout the week, especially over the Cascades
and Olympics, where ensembles show potential for MUCAPE values as
high as 500-1000 J/kg. While the exact details remain highly
uncertain at this time, the threat for storms continues to be
closely monitored.

15

&&

.AVIATION...A shallow trough in north B.C. will slowly
fig southward today. The flow aloft will increase and turn from
zonal to slightly west-southwest as it digs down over WA into
Saturday. Stratus remains in place this afternoon along the coasts,
Southwest Interior up into Kitsap/Puget Sound terminals. Terminals
under the stratus remain MVFR this afternoon. Satellite shows
clearing taking place on the east side of the Cascades (particularly
south of I-90), and also some clouds eroding along the east Strait
of Juan de Fuca. Given the lingering stability and lack of solar
input to mix up, the cloud deck will linger a bit longer through the
afternoon. Scattering of the main deck is anticipated from 20-22Z
(though the coast will likely remain MVFR due to the onshore
pattern). Winds this afternoon are still southwesterly 4 to 8 kt
(gusty at KBLI to 20 kt and also Strait of Juan de Fuca areas due to
push. Diffluence from the marine push through the strait will turn
winds lightly northerly from 02-04Z through 09Z in Puget Sound.

Another marine push Saturday morning will likely bring stratus.
There is a 40-60% chance of MVFR in interior terminals, and 60-90%
from Olympics to the coast. Highest chance of IFR (20-40%) is most
of the coast, Olympics, Hood Canal, Kitsap, and north Puget Sound
terminals. Some mist and possible drizzle may mix in spots.
Improvements to VFR expected 18-21Z.

KSEA...MVFR Cigs expected to scatter this afternoon between 20-22Z,
with either SCT or FEW likely remaining in the evening around or
below 5,000 ft. Southwest winds this afternoon 4-8 kt will likely
turn northwest after 02-04Z through 9Z (expected at or below 5 kt),
before returning to the southwest. Another marine push likely to
bring stratus/mist and possible drizzle in the morning (as early as
12Z lasting 18-21Z) - 40% chance of MVFR and 15% chance of IFR.

HPR

&&

.MARINE...An upper level trough will bring increasing onshore flow
today over the region. The trough will remain in place through
Saturday before moving inland. A larger low will dip down from
Alaska offshore through next week.

For this weekend, the onshore marine pushes may bring stratus and
mist/fog over portions of the waters Saturday morning (especially
the inner coastal waters). Diurnal pushes through the Strait of Juan
de Fuca will continue through the weekend. A small craft advisory
continues for the central/east Strait of Juan de Fuca this evening,
and the push Saturday evening/Sunday may produce gusts and
potentially sustained small craft winds. Coastal seas will remain

Seas will remain 5 feet or less throughout the weekend through next
week.

HPR

&&

.FIRE WEATHER...No fire weather concerns through Monday. Conditions
will start to warm up and dry out early next week as an upper level
ridge begins to build over the Pacific Northwest. Concerns begin to
increase going into the middle of next week as a trough slowly
drifts south out of the Gulf of Alaska, and the flow aloft over the
region turns southerly. This will allow for more moist air from the
Pacific to move into the region and this pattern is indicative for
the potential for thunderstorm development. While significant
positive precipitable water anomaly values point towards mostly wet
thunderstorms, fuels will be dry enough that any lightning could
prove problematic. More details will be available as we get into
next week, but we will continue to closely monitor how the pattern
evolves.

62

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 2 AM PDT
     Saturday for Central U.S. Waters Strait Of Juan De Fuca-
     East Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$