Washington State Forecast Discussion

Western Washington


903
FXUS66 KSEW 160923
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
223 AM PDT Wed Apr 16 2025

.SYNOPSIS...A dry, warmer pattern will continue through Friday
across Western Washington with upper ridging. A weak frontal
system will move through on Saturday with cooler temperatures and
increasing shower potential. Additional shower chances and cooler
temperatures Sunday into Monday with troughing over the Pacific
Northwest.

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.SHORT TERM /TODAY THROUGH FRIDAY/...Generally clear skies for
most of Western Washington early this morning with a few mid
level clouds across central Puget Sound due to weak convergence
around 850 MB. Some clouds may also be around this morning across
the Southwest Interior, otherwise, clear skies for most of Western
Washington today. Upper ridging continues to build offshore into
Thursday for increasing northerly flow and slowly warming
temperatures. Highs Wednesday and Thursday will be in the 60s for
most areas. Temperatures are expected to peak for most areas on
Friday as the SW/NE oriented ridge axis moves over Western
Washington, with highs in the mid 60s to low 70s.

.LONG TERM /SATURDAY THROUGH TUESDAY/...The upper ridge will
flatten over the Pacific Northwest Friday night into Saturday as a
weak frontal system moves across Western Washington. An uptick in
precipitation potential is expected during this period, although
QPF amounts are generally light (under 0.10" for the lowlands),
and favored in the Cascades as well as in any convergence areas.
Ensembles are in good agreement that troughing remains in place over
the Pacific Northwest Sunday into Monday for continued cooler
temperatures. Weak ridging may again build into the region Tuesday.
Temperatures are expected to range near to slightly below normal
over the weekend and into early week. JD

&&

.AVIATION...Northwesterly flow aloft this morning will turn more
northerly this afternoon as an upper level trough dives southward
into eastern Washington throughout the day. Surface winds currently
representing light onshore flow, turning northerly by late morning
with speeds increasing to 10-15 kts especially for the eastern half
of the CWA.

Widespread VFR conditions over W WA this morning with most terminals
reporting clear skies or only high clouds. The exception being a
patch of clouds present over the southern half of Puget Sound,
impacting SEA, BFI and PWT. Cigs still fall very comfortably into
VFR conditions with bases at their lowest at PWT at 4000 ft and at
their highest at SEA and BFI at 6000 ft. Satellite trends show some
thinning out, so inherited forecast scattering out this layer around
12Z still seems on track. VFR conditions are expected to remain in
place for all terminals for the entire TAF period.

KSEA...VFR conditions in place and expected to remain that way for
the TAF period. See above discussion regarding current cigs, trends
and impacts to the forecast. Depending on how long these clouds
linger, may need to adjust either timing or cigs of 12Z line in
current TAF. Light northerly winds this morning with speeds largely
under 5 kts before an increase in speed to 10-15 kts around 20Z with
possible gusts impacts the terminal this afternoon. These speeds
will gradually ease by 12Z Thursday.

18

&&

.MARINE...High pressure over the northeastern Pacific
extending over the waters will continue into Friday. A pair of
weak systems will move through the area over the weekend.

Combined seas over the coastal waters in the 10 to 12 foot range
through Wednesday. Seas for the outermost coastal waters could reach
14 feet throughout the day today. Winds as high as 30 knots in the
outer coastal waters still possible early this morning before
gradually easing. Inherited SCA for the coast looks good and remains
in effect until 6 PM this early evening. While current forecast
suggests speeds should remain just under criteria, isolated
northerly winds in Puget Sound might encroach on SCA criteria. This
will need to be monitored. A Small Craft Advisory for rough bar
conditions at the Grays Harbor Bar also looks valid and will
therefore go untouched. Seas subside tonight back into the 4 to 6
foot range later Thursday and Thursday night.

18

&&

.HYDROLOGY...No river flooding expected during the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 PM PDT this evening for Coastal
Waters From Cape Flattery To James Island 10 To 60 Nm-
Coastal Waters From Cape Flattery To James Island Out 10 Nm-
Coastal Waters From James Island To Point Grenville 10 To
60 Nm-Coastal Waters From James Island To Point Grenville
Out 10 Nm-Coastal Waters From Point Grenville To Cape
Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
To Cape Shoalwater Out 10 Nm-Grays Harbor Bar.

&&