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000
FXUS66 KSEW 232241
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
341 PM PDT Tue Apr 23 2024

.SYNOPSIS...Weak front offshore moving inland Wednesday. This will
mark the beginning of a cool and wet last week of April with an
upper level trough over the area and a couple of systems moving
through over the weekend and Monday. Snow levels will lower over
the weekend to near 3000 feet Monday for possible snow on all the
mountain passes the first part of next week.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Satellite imagery shows
some high clouds over Western Washington this afternoon.
Approaching front still well to the northwest over Northern
Vancouver Island. Temperatures at 3 pm/22z were in the 60s and
lower 70s.

Low level offshore flow will transition to onshore this evening
with a weak surface ridge out ahead of the next frontal system.
Front moving slowly down from the northwest will still be offshore
by 12z Wednesday. Rain out ahead of the front could reach the
north coast early Wednesday morning. Increasing clouds overnight
will keep low temperatures in the 40s.

Weakening front moving through Western Washington Wednesday. Front
reaching the coast late morning moving through the interior in
the afternoon before hanging up over the Cascades late in the
afternoon. Not much in the way of rain with the front with most
places getting less than a tenth of an inch. Main story for
Wednesday will be the cooler high temperatures, 10 to 15 degrees
cooler than Tuesday, in the mid to upper 50s.

Upper level trough over the area Wednesday night keeping a chance
of showers in the forecast. Mostly cloudy skies and weak low level
onshore flow will keep low temperatures in the mid to upper 40s.

Much more organized system moving into Western Washington
Thursday with a half inch to an inch of rain along the coast with
higher amounts over the Olympics and lesser amounts over the
interior and the Cascades. Snow levels around 4500 feet so no snow
in the lower passes. Highs Thursday remaining cool, in the mid
50s.

Front becoming a little negatively tilted with the associated
surface low moving south along the coast. This will slow the
eastward movement with frontal passage not until later Thursday
night/early Friday morning. Another half to one inch of rain
possible along the coast and in the Olympics with a quarter to a
half inch elsewhere. Rainfall totals with this front will be about
equal to the total rainfall so far for April in some places. Lows
in the mid 40s.

Upper level trough moving over Western Washington behind the front
Friday for more showers across the area. Not much in the way of
cool air associated with the trough with snow levels remaining
above 4000 feet. Highs Friday in the 50s.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Extended models in good
agreement with a splitting front arriving over the weekend and
another front on Monday. Very cool upper level trough settling
into the area later Monday into Tuesday with 500 mb temperatures
as low as -30C. Snow levels lowering to near 3000 feet Monday for
the possibility of snow on all of the mountain passes Monday and
Tuesday. Highs remaining below normal, in the 50s, with lows in
the upper 30s to mid 40s. Felton

&&

.AVIATION...Winds aloft west-southwesterly as a broad upper-level
trough approaches the area from the northwest. VFR conditions
dominate for the majority of the TAF period for most locations. A
blanket of high clouds will continue, with increasing mid to low
level cloud cover tonight as a weak cold front approaches from the
northwest. The best chances for MVFR ceilings are along the coast
after 09-12Z Wednesday. Isolated IFR conditions may be possible
Ceilings should be low-end VFR through the interior terminals, with
a 20-25% chance of MVFR ceilings after 18Z Wednesday. Rain showers
should be limited to the Pacific Coast and the north interior (BLI),
but a few showers/drizzle may be possible through the remainder of
the region Wednesday.

Winds generally west/northwesterly 5-10 kt. Winds decrease tonight
and switch to southwesterly tonight. Winds will pick up in speed
tomorrow morning back to 5-10 kt.

KSEA...VFR conditions expected through the TAF period. High clouds
continue with increasing low-to-mid level cloud cover tonight. Winds
WNW 5 to 10 kt in the afternoon before a transition to light
southerly tonight. Winds increase back to 5 to 10 kt but remain SW
tomorrow. A few showers are possible but should be light and not
impactful.

LH

&&

.MARINE...Weak thermal troughing continues to work onshore and
dissipate as a weak front approaches the region from the northwest.
Winds will increase through the Strait of Juan de Fuca this evening,
with the Small Craft Advisory for the Central and Eastern Strait of
Juan de Fuca in effect through early tomorrow morning. The
aforementioned front will approach the area early tomorrow morning
but will dissipate as it does so, leaving only scattered showers and
minimal impacts. A more substantial system will move through the
area waters on Thursday, however, winds look to remain under
advisory thresholds. A weak surface ridge will momentarily ease the
winds for Saturday before an active pattern begins Sunday.

Seas look to remain 4 to 6 feet at about 10 seconds through the
rest of the week and into Saturday.

LH

&&

.HYDROLOGY...No river flooding expected in the next 7 days.
Heavier rain over the south slopes of the Olympics Thursday and
Thursday night could push the Skokomish River in Mason county
close to action stage Friday. Felton

&&

.CLIMATE...With cool weather ahead for the end of the month the
warmest day in April in Seattle will be 72 degrees on the 20th.
For only the 7th time in 80 years of records at Seattle Tacoma
airport the warmest day in March, 74 degrees on the 16th, will be
warmer than the warmest day in April. Other years this has
occurred, 2019, 1995, 1994, 1969, 1964 and 1948. For those
looking forward to warmer weather there has been at least one 80
degree plus day in Seattle in May in 11 out of the last 12 years.
Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 4 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$