627
FXUS66 KSEW 172108
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
208 PM PDT Mon Aug 17 2026

.SYNOPSIS...Dry and mild weather will persist through midweek. Shower
and mountain thunderstorm chances increase heading into Friday
and Saturday as the next system moves in. Quiet weather returns
for the first half of next week.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...Generally
mild/benign weather for western WA through midweek. Currently,
we sit under weak/split flow with high pressure to our south and
low pressure offshore. The flow pattern remains onshore with
temperatures close to average. High pressure remains nearly
stationary moving toward midweek with ongoing dry weather across
western Washington. 33

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...Low pressure starts to
shift east and inland Friday and Saturday for a chance of
showers and cooler conditions. Most of the shower activity will
be over the coast and mountains and there is a slight chance of
thunderstorms in the northern Cascades Saturday afternoon. With
the trough overhead, Saturday`s highs will be cooler and in the
60s to lower 70s. The trough exits east Saturday night and
we`re back to our dry and mild conditions Sunday and Monday with
temps very close to our averages. 33

&&

.AVIATION...VFR this afternoon will prevail across the terminals.
Conditions will deteriorate this evening first along the coast
and later across interior terminals by the morning as another
round of stratus pushes inland. Latest guidance suggests Puget
Sound terminals will see MVFR cigs. IFR/LIFR conditions expected
for locations along the coast, Strait of Juan de Fuca, and
Kitsap Peninsula. In addition, reductions in visibility possible
with the marine push. NW winds this afternoon will shift SW by
Tuesday morning.

KSEA...VFR will prevail through the day. Another push of marine
stratus is expected to bring MVFR cigs to the terminal after 12z.
Clouds expected to lift and scatter in the afternoon after 18z. NW
winds this afternoon around 5-7 kt will transition to SW late
tonight into Tuesday morning around 3-5 kt. Increasing SW in the
afternoon to 6-9 kt.

&&

.MARINE...High pressure will remain over the far offshore
waters and slowly build into area waters through the middle of
the week, which will maintain northwesterly winds over the
coastal waters. A weak system will approach area waters on
Tuesday, with little impact to the waters. Northwesterly winds
look to increase late tonight into Tuesday over the outermost
waters, which may develop steep seas around 6-7 ft with a
dominant period of 7 seconds. The threat for steep seas may
continue through mid-week. High pressure will weaken late in the
week as a frontal system passes over the coastal waters. Weak
westerly pushes down the Strait of Juan de Fuca will continue
this week. The next round of westerlies that may exceed 21 kt is
Friday, with the latest probabilities around 40-60%.

62/29

&&

.FIRE WEATHER...The weather pattern will remain fairly stagnant
over the next few days, with onshore flow promoting healthy
relative humidity values. An upper level ridge will build
northward towards the Pacific Northwest during the latter half
of the week, bringing a mild warming and drying trend to western
Washington.

The next weather system is favored to cross the region late Friday
into the weekend, with potential for thunderstorms to develop over
higher terrain leading to elevated fire weather conditions. While
precipitation amounts may bring localized wetting rains to the
region, any storms that develop will also be capable of generating
gusty and erratic outflow winds and abundant lightning. While the
exact timing and location of thunderstorms remains uncertain at this
time, the threat of overnight thunderstorms remains into the
weekend, particularly Friday night into Saturday.

15

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$