Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 230352
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
852 PM PDT Fri Mar 22 2024

.UPDATE...Satellite imagery shows upper level low off the Central
Oregon Coast near 43N/127W, a little further east than the models
position. Showers rotating around the low over Western Washington
this evening. Doppler radar showing enhanced echoes near the coast
but with the low further east the flow aloft over Western
Washington is southerly so these showers should stay along the
coast and offshore. Low will continue to drift east tonight into
Saturday with a deformation zone setting up near the Canadian
border Saturday. This is where the heaviest precipitation will
occur. Current forecast on track. No updates this evening. Felton

&&

.SYNOPSIS...An upper low offshore will slowly move eastward and
move inland later Saturday bringing periods of rain. A weak, brief
upper ridge offshore on Sunday. A series of weather systems will
then move through Western Washington Monday through Thursday
bringing lowland rain and mountain snow.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Steady light rain across
portions of Western Washington this afternoon with an upper low
slowly moving eastward offshore of Oregon. This initial band will
push northward through the evening hours. Another round of
steadier rain is then expected to slowly move north tonight
through Saturday for additional lowland rain. Snow levels will
generally range 4000-5000 feet for some accumulating snowfall at
Stevens Pass. The upper low offshore will then move inland and
slide eastward Saturday night into Sunday. Brief ridging offshore
is expected on Sunday, however, with northwest flow aloft, clouds
and showers will likely linger on Sunday for some areas,
especially Snohomish County southward. There will likely be some
areas of clearing Sunday afternoon into Sunday night. Another weak
system will move into Western Washington on Monday for lowland
rain and light mountain snow. Highs in the 50s through the
weekend.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Troughing will be over
Western Washington Tuesday for continued showers chances and
onshore flow. Ensemble guidance suggests a stronger system may
impact the area on Wednesday with a deeper upper low approaching
the coast. Steadier lowland rain, as well as periods of mountain
snow and breezy winds, is likely mid-week with this system.
Ensemble guidance is consistent in continued troughing Thursday
and Friday for additional precipitation. Cooler temperatures, a
few degrees below normal, is expected through next week with
highs in the low to mid 50s for Western Washington. JD

&&

.AVIATION...Southerly flow aloft into at least Saturday afternoon as
an upper level low slowly shuffles eastward. Cigs generally VFR for
most spots however there are still some MVFR to IFR spots thanks to
lingering scattered showers over W WA this evening. Even as these
taper off as the night progresses, there will be enough low level
moisture for cigs to lower with most terminals dipping down into
consistent MVFR conditions during the overnight hours after 06Z.
Locations more prone to lower cigs /OLM, PWT/ may see vis reductions
or patchy fog. Conditions do look to improve in the 18-20Z time
frame Saturday with more widespread VFR conditions expected to re-
emerge.

KSEA...VFR conditions in place at the time of this writing /02Z/,
however showers passing over the terminal have resulted in
occasional MVFR conditions with vis reductions. By the time more
consistent rain moves over the terminal around 06Z tonight, MVFR
conditions expected to be in place and remain so into Saturday
afternoon as precip starts to taper off. As that happens, VFR
conditions will return. NW winds at 5-10 kts remain in place,
turning southerly overnight after 06Z and easing to around 5 kts.
Northerly winds return Saturday afternoon.

18

&&

.MARINE...A surface low continues to meander offshore throughout
the weekend, with little to no impact expected across the coastal
waters. Conditions over the interior waters also look to remain on
the quieter side through the weekend and into the first half of next
week. Active weather is expected to return by midweek as a stronger
system enters our area, which may give rise to the potential for
headlines.

Combined seas 3 to 6 feet will remain throughout the weekend and
into the beginning of next week, before rising midweek.

18/Maz

&&

.HYDROLOGY...No river flooding is expected the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$


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