Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
458
FXUS66 KSEW 160945
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
245 AM PDT Sat May 16 2026
.SYNOPSIS...
Very cool upper level trough over Western Washington today will
move south tonight and Sunday. Upper level ridge building
Sunday with the ridge axis offshore extending into Southern
British Columbia. The ridge will remain through the week with
weak systems passing by to the north at times.
&&
.SHORT TERM /TODAY THROUGH MONDAY/...
Satellite imagery shows mostly cloudy skies over Western
Washington this morning with an upper level trough over the area.
Plenty of showers on the Doppler radar with a rain shadow
evident over the Central Puget Sound. Temperatures at 2 am/09z
were in the mid 40s.
Upper level trough remaining over Western Washington today. Very
cold for May temperatures aloft with 500 mb temperatures
around -30C. Air mass slightly unstable this morning will
become more unstable this afternoon. Convective indices by 21z
include lifted index of 0 to -2, lapse rates plus 7 to 8C/km,
convective temperatures in the lower 50s and even 500 J/kg of
CAPE. Scattered showers this morning with the rain shadow
continuing over the Central Puget Sound. With the convective
temperatures in the lower 50s will take a little daytime heating
to fire things up with thunderstorm chances increasing around
midday in addition to increasing showers. Convergence zone
developing late in the afternoon. Flow aloft northwesterly which
will push the convergence zone development location a little
further south than usual, mostly likely over Seattle. The very
cold air aloft means heavier showers at any point during day
could produce small hail. Snow levels remaining near 3500 feet
with the possibility of briefly lower snow levels in the
stronger showers. Winter weather advisory for the mountains
will remain in effect. Another cool day with highs only in the
lower to mid 50s. Olympia was the only location Friday to tie a
record low maximum temperature. Like Friday highs mostly only a
couple of degrees above the record low maximums.
Upper level trough digging south tonight with shower activity
decreasing in the evening. The exception to this will be the
convergence zone which will remain between Seattle and Olympia
extending southeast into the Cascades. The zone will dissipate
after midnight. Snow levels remaining near 3500 feet bringing a
few inches of snow to the Cascades south of Snoqualmie Pass. The
winter weather advisory will continue overnight. Lows in the
mid 30s to lower 40s.
Upper level ridge building offshore Sunday with the ridge axis
nosing into Southern British Columbia. Low level flow going
light. This combined with plenty of low level moisture will
produce a mostly cloudy morning, especially over the interior.
More sunshine in the afternoon. Highs warming into the mid 50s
to lower 60s. Still about 5 degrees below normal.
Little change in the pattern Sunday night and Monday. Low clouds
forming Sunday night with the light flow in the lower levels.
The marine layer at this point does not look deep enough to
continue much past midday Monday. Lows in the upper 30s to mid
40s. Highs getting back to normal, in the 60s. Felton
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Models in good agreement with the upper level ridge remaining
over the area into Friday although the ridge does flatten out a
bit beginning Wednesday. Weak systems moving over the top of the
ridge will keep the low level low weakly onshore through the
period. This will prevent temperatures from warming very much.
Highs in the 60s Tuesday, 60s and lower 70s Wednesday through
Friday. Lows mostly in the 40s and lower 50s.
&&
.AVIATION...
Westerly flow aloft will become more northwesterly this morning
and then more northerly by late tonight as an upper level trough
moves across the area. Onshore flow continues in the low levels,
with breezy west/northwesterly winds persisting at coastal terminals,
with gusts to 20-25 kt. Winds across the interior remain southerly,
primarily between 7-12 kt. Radar shows widespread scattered shower
activity across western Washington this morning, which is resulting
in a mixed bag of VFR to MVFR conditions across the area terminals.
Shower activity will continue throughout the day for a continued
mixed bag of conditions, with guidance showing a strong signal
for a PSCZ developing across the central Sound this afternoon
and evening. Isolated thunderstorm activity will be possible
throughout the day, but confidence in occurrence is too low for
inclusion in any single TAF site at this time. Southerly winds
will persist between 7-12 kt through the day for interior
terminals, but could briefly shift northerly this afternoon
within the vicinity of the convergence zone. Showers will taper
area-wide heading into Sunday morning.
KSEA...A mix of VFR to MVFR conditions expected throughout the
day with shower activity. Hi-res guidance continues to indicate
a convergence zone moving into the terminal between 21-00Z. Southerly
winds will persist through the morning hours, primarily between
7-12 kt, but will become variable in the vicinity of the PSCZ
and then shift to the north for a few hours this afternoon and
evening. Isolated thunderstorm activity will be possible, with
latest guidance highlighting a 15-20 percent chance of lightning
within the convergence zone, but confidence is too low to include
in the TAF at this time.
14
&&
.MARINE...
A system moving through the region today will enhance winds and
seas over most of the area waters with small craft advisory
conditions expected for the coastal waters and along the Strait
of Juan de Fuca. The increase in onshore flow could even bring
a few gale gusts to portions of the central and eastern Strait,
with the latest HREF probabilistic guidance indicating roughly
a 50-60 percent chance of gusts briefly exceeding 34 kt this
afternoon. Showers and a slight chance of thunderstorms will be
possible across the area waters as well today, which could bring
brief drops in visibilities in any heavier shower activity.
Seas will build to above 10 ft across the coastal waters today
and could become steep at times.
High pressure will build back into the area waters on Sunday,
before a weak frontal system approaches and moves into the area
waters Monday into Tuesday. Onshore flow will persist and will
result in daily pushes of westerly winds through the Strait of
Juan de Fuca through the first half of next week. High pressure
will then build back into the waters again by Wednesday. Seas
will generally persist between 6-9 ft Sunday into early next
week, though could build back to near 10 ft around Monday into
Tuesday.
14
&&
.HYDROLOGY...
The daily hydrology discussion has ended until the start of the
next rainy season; it will only be updated during this time as
needed.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 8 AM PDT Sunday for Cascades of
Pierce and Lewis Counties-Cascades of Snohomish and
Northern King Counties-Cascades of Southern King County-
Cascades of Whatcom and Skagit Counties-Olympics.
PZ...Small Craft Advisory until 5 PM PDT this afternoon for Grays
Harbor Bar.
Small Craft Advisory from 6 AM this morning to midnight PDT
tonight for Central U.S. Waters Strait Of Juan De Fuca-
West Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from noon today to midnight PDT tonight
for East Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 4 AM PDT early this morning for
Puget Sound and Hood Canal.
Small Craft Advisory until 11 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.
&&
$$
NWS SEW Office Area Forecast Discussion