Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 182118

Area Forecast Discussion
National Weather Service Seattle WA
218 PM PDT Tue Jun 18 2024

.SYNOPSIS...High pressure aloft will gradually build through the
week, allowing conditions to dry out and warm up. A pattern change
is on track for the weekend as a trough brings wetter and cooler
conditions to western Washington.


.SHORT TERM /TONIGHT THROUGH FRIDAY/...Cloud cover will continue
to break up throughout the afternoon and evening tonight as a
broad upper level trough continues to weaken and exit to the east.
Lingering moisture and cool air aloft, mostly confined to the
far north and east side of the Cascades, may promote a few
isolated showers and thunderstorms this evening and tomorrow
evening, but no significant rainfall is expected on the west side
of the crest. Elsewhere, clouds should be mostly gone by tonight
and remain like so through the short-term period. As a result,
daytime highs will increase each day.

Highs Wednesday should be in the mid to upper 70s to near 80 in
the Southwest Interior, increasing to the upper 70s to low 80s,
with mid 80s possible through the Southwest Interior. Friday looks
to be the warmest day for most as the upper level ridge axis
moves over the region, with temperatures reaching the mid 80s for
most of the interior. Minor HeatRisk will dominant the short-term
period. Pockets of Moderate HeatRisk, most notably in the urban
cores (including Seattle, Tacoma, and Olympia), as well as the
Cascade Valleys, will put heat stress on vulnerable populations in
these areas. Clear skies and light winds will allow overnight
lows to fall into the low to mid 50s, which is helping to limit
significant heat impacts. Onshore flow along the Pacific Coast and
the Strait of Juan de Fuca will help moderate daytime
temperatures there into the 70s.

.LONG TERM /SATURDAY THROUGH TUESDAY/...A shift in the pattern is
in store for the long-term as a large trough will come down from
the Gulf of Alaska. Cloud cover will begin to increase on
Saturday, allowing highs to cool back into the upper 70s. An
associated surface cold front will move through late Saturday into
Sunday, bringing another round of rain showers and breezy winds.
Showers will be most likely along the Pacific Coast and higher
elevations, with amounts remaining very low. The pattern next
week looks to favor an active pattern with several systems moving
through and temperatures remaining below normal.



.AVIATION...North-northwesterly flow aloft with high pressure
building into W WA this evening. VFR conditions this afternoon
will continue into the overnight period as remaining clouds begin
to lift and scatter out. High clouds may linger around this
evening but overall, VFR will continue into Wednesday morning, the
exception being KHQM - where there is a good indication of
MVFR/IFR marine stratus lasting through Wednesday morning. Mostly
clear skies for the interior.

Westerly winds this afternoon will turn northerly across the
interior and remain around 5 to 10 kts.

KSEA...VFR conditions in place this afternoon will continue
throughout the TAF period, with clouds scattering out late this
evening. Westerly winds this afternoon will start to turn to the
north around 22z-00z with speeds around 5 to 10 kts, generally
remaining unchanged into Wednesday morning.



.MARINE...A broad area of high pressure situated just offshore
will continue to influence the pattern throughout the week.
Occasional westerly pushes down the Strait of Juan De Fuca will
be likely during this period, but latest trends show that most of
these pushes will be below any headline criteria. A frontal
system will approach the area waters this weekend introducing
showers, but winds look to remain mostly the same - however
additional pushes down the Strait of Juan De Fuca will continue.

Combined seas will remain 4 to 6 ft through the remainder of this
week, rising around 6 to 8 ft beginning this weekend.