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000
FXUS66 KSEW 240253
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
753 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/...Forecast remains on track
this evening as a mild evening continues for some of the interior.
Increasing high clouds already overhead with a transition to low-
level onshore flow underway ahead of the next frontal system.
Previous discussion remains valid and follows.

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 remain west-southwesterly into at least
Wednesday morning as a broad upper-level trough approaches the area
from the northwest. Surface winds generally west/northwesterly 5-10
kt at most terminals this evening before decreasing somewhat to 4-8
kts and shifting to the southwest tonight. Speeds expected to
increase back to 5-10 kts Wednesday morning although direction will
remain the same.

VFR conditions with mainly high clouds over W WA this evening, but
will start to see cigs lower overnight as mid-level clouds start
working into W WA ahead of the next system. Conditions will continue
to erode as the system starts to enter the region by late Wednesday
morning/early afternoon...however cigs are expected to remain
largely within VFR criteria. The only exceptions to this may prove
to be HQM and OLM. HQM being not only the westernmost terminal and
thus first to be impacted but also being more prone to lower cigs
may see MVFR to even possibly IFR conditions as early as the
overnight hours and extending into the remainder of the TAF period.
Models remain in some disagreement with OLM, however latest trends
also suggest MVFR conditions starting as early as overnight tonight
or as late as late Wednesday morning. Will need take this recent
trend into account for the 06Z TAF. Low model confidence in the
prospect of precip Wednesday at current will prevent TAF mention at
this time. Some sites contain VCSH to cover this and will leave that
stand for the time being.

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 this evening 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.

18/LH

&&

.MARINE...Weak thermal troughing continues to work onshore and
dissipate as a weak front approaches the region from the northwest.
Winds in the Central Strait hitting SCA criteria while the East
Entrance is seeing gusts that fall within criteria...but sustained
have not quite ramped up just yet. Given the speeds being seen in
the Central portion, fairly confident that these speeds will
translate further eastward and as such, inherited Small Craft
Advisory looks good and will remain unchanged. 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. At this time, winds look to remain under advisory
thresholds. A weak surface ridge will momentarily ease wind speeds
for Saturday before an active pattern re-emerges Sunday.

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

LH/18


&&

.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.

&&

$$