833
FXUS66 KSEW 171530
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
830 AM PDT Sat May 17 2025

.SYNOPSIS...An upper level trough will continue to produce
showers through the weekend, with an isolated chance of
thunderstorms Saturday afternoon. Additional disturbances will
bring showers across the region through next week, with
precipitation chances decreasing through the week. Temperatures
will slowly climb a few degrees going into the next week, with
highs climbing from around 60 to near 70 in the lowlands.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...Showers today with a trough
moving through. Will also see convergence zone activity in the
central sound with a chance of thunderstorms too this afternoon.
Temps only in the 50s to lower 60s today. 33

Previous discussion...This morning`s trough is beginning to move
onshore, with a weak cold front draping along in southern WA/OR.
A surface trough also sits just east of the Cascades and is acting
as a post-frontal boundary.

Radar remains active with several bands of showers moving
northeastward towards the Canadian border. The strongest of these
showers was localed just offshore of Grays Harbor County. Cooler
air aloft associated with the trough has helped to destabilize
the atmosphere somewhat for the potential for afternoon convection
(in the form of thunderstorms). Instability is expected to
increase up to 200 J/kg through the late morning and afternoon. As
the trough digs southward across western WA this afternoon, the
positive vorticity advection should help to aid in
afternoon/evening convection across our region. The two ares the
HREF were pinging for ingredients was the south Puget Sound area,
and up near Bellingham. Some small graupel and gusty winds may
accompany the strongest storms, but otherwise no severe storms
are expected. The convection later today may organized into a
convergence zone that continues into the overnight. Highs
Saturday will climb into the low 60s for most lowland spots.

Showers are expected to continue Sunday morning and start to taper
back as a break in between systems (late Sunday morning through
Sunday night). The cool air associated with the trough will drop
snow levels just north of 3,000 ft (which will mix some of the
precipitation that falls). Light snowfall accumulations are
possible with the system passing through today in the Cascades
(and to a weaker extent the Olympics).

Monday will see an organized frontal system sweep across western
WA. The best chance of thunder will be up in the Neah Bay area
into the waters (late Monday afternoon/evening).

.LONG TERM /TUESDAY THROUGH FRIDAY/...Late Tuesday through the
rest of the work week is expected to be drier (though not shower-
free at times due broad troughing over the Pacific). Most models
favor wet/dry pattern to continue through the end of the work
week. Temperatures are expected to slowly climb through the week,
with a couple spots in the Southwest Interior expected to hit
around or close to 70 next Saturday.

HPR

&&

.AVIATION...Upper level trough over the area today will shift
east tonight. Weak upper level ridge building offshore Sunday.
Southwesterly flow aloft becoming westerly this morning and
northwesterly tonight. In the lower level increasing onshore flow
with low level convergence over the Puget Sound area into this
evening.

Generally MVFR ceilings this morning. Convergence developing over
the Central Puget Sound with IFR ceilings at times this morning
becoming more prevalent this afternoon. Ceilings in the Central
Puget Sound lifting to MVFR tonight. Outside of the Central Puget
Sound ceilings improving to low end VFR later this afternoon
lowering back down to MVFR tonight.

KSEA...MVFR ceilings this morning with IFR at times. IFR ceilings
late morning through the afternoon hours. Ceilings lifting back
up to MVFR this evening into Sunday morning. Light winds this
morning could turn briefly north less than 5 knots. Winds becoming
southwest 4 to 8 knots this afternoon and 10 to 15 knots tonight.
Felton

&&

.MARINE...Weak front dissipating over the waters this morning. Surface
high pressure will rebuild over the coastal waters tonight into
Sunday. The next frontal system will arrive on Monday. Another
system will follow later Tuesday. High pressure will build over
the area Wednesday.

Gale warning for the Central and Eastern Strait beginning this
afternoon and continuing through tonight. Small craft advisory
winds for the remainder of the waters late this afternoon through
Sunday morning with the exception of the Puget Sound where
converging winds will keep speeds 20 knots or less. Winds easing
all waters later Sunday into MOnday.

Seas building to near 10 feet over the coastal waters Monday night
into Tuesday night behind the system moving through the waters
Monday. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 11 AM PDT
     Sunday 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-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 3 PM this afternoon to 5 AM PDT Sunday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Sunday
     for Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 3 PM this afternoon to 5 AM PDT Sunday
     for Admiralty Inlet.

&&

$$