814
FXUS66 KSEW 130326
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
826 PM PDT Sun May 12 2024

.SYNOPSIS...Upper level ridge will continue to exit to the east
today. A weak upper level trough moves through on Monday. Another
upper level ridge will build in from the west on Tuesday and
remain in place through the remainder of the week. An upper level
trough may develop and move through late week into the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Cloud coverage will
continue to increase tonight as a weak shortwave impulse passes
over western Washington into tomorrow. This, along with surface
high pressure over the eastern Pacific pushing closer to the coast
will allow for a westerly push of the marine layer on Monday
along the coast and develop mostly cloudy conditions through the
interior. A few light showers are possible in the Cascades and
foothills as well as the potential for a convergence zone over
Snohomish/northern King County. High temperatures will be again be
around 10 degrees cooler than today, into the upper 50s to 60s, a
few degrees below normal for most.

Surface high pressure broadens on Tuesday and into Wednesday as
an upper level ridge develops and approaches the region from the
west. High temperatures will bounce back into the 70s with dry
conditions and mostly clear skies, with the exception of the
marine layer along the coast.

.LONG TERM /FRIDAY THROUGH MONDAY/...Model guidance is still
somewhat dissonant with a 10 to 15 degree range in high
temperatures between the 25th and 75th percentile Thursday and
beyond but the synoptic pattern is beginning to look more
consistent for the long term forecast. Expecting mostly dry
conditions on Thursday. An upper level trough will move through
British Columbia and into southern Alberta, and some ensemble
members are hinting that the associated surface frontal system may
produce some showers in the Cascades on Thursday and into Friday.
Elsewhere, conditions will be mostly dry. Another upper-level
trough may approach the region next weekend, but deterministic
models disagree on the exact evolution and many ensemble members
keep conditions dry through the weekend.

LH

&&

.AVIATION...Westerly flow aloft will back to southwesterly
tonight as an upper ridge gives way to a weak upper trough and
associated front that will cross the region late tonight into early
Monday. Increasing onshore low-level flow will bring a push of IFR
to low MVFR stratus to the coast this evening. Meanwhile, expect
ceilings to gradually lower into the MVFR range early Monday morning
with gradual lifting to VFR possible later in the day.

KSEA...VFR with increasing high level moisture and cloud cover
expected through the evening. Ceilings expected to fall to the
low end of MVFR by 12Z-15Z Monday. Increasing N/NE surface winds
to 10-13 kt as a weak shortwave approaches. Confidence on wind
direction becomes lower after 09z, with the most likely scenario
being a return to southerly winds. However, if the onshore push
through the Strait of Juan de Fuca is stronger, this could create
a more variable wind direction or delay this switch.

Cullen/Lindeman

&&

.MARINE...Onshore flow continues as a weak system approaches
the area across the north. Elevated winds through the Strait of
Juan de Fuca through the early morning Monday. The gale warning remains
in effect, with small craft advisories for the adjacent waters.
Another round of gusty winds is possible Monday night as well with
the following disturbance so will see how winds develop with this
round and consider any needed extensions or subsequent warnings or
advisories.

Meanwhile, seas remain rather steep across the coastal waters this
after noon. This, coupled with continued gusts into the 20-25 kt
range, warrants the continued advisory through this evening. Expect
that the winds over the coastal waters will ease and the dominant
period to lengthen a bit, so this advisory will run through 11 PM as
planned for now.

Onshore winds look to temporarily weaken around midweek, but again
likely strengthen later in the week. Seas over the coastal waters
will build a bit with each passing system to 7 to 9 feet with
periods remaining short (around 8 seconds).

Cullen

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 4 AM PDT Monday for Admiralty Inlet-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 4 AM PDT Monday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 3 AM PDT Monday for Northern Inland
     Waters Including The San Juan Islands.

     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.

&&

$$