687
FXUS66 KSEW 122209
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
309 PM PDT Thu Mar 12 2026
.SYNOPSIS...
Weak atmospheric river will bring continued rain showers
throughout today and into Friday, with the chance of a rain/snow
mix early Friday morning. Upper level troughing will keep
showers around the area into Saturday. A warm front will then
move over the region Sunday into Monday, bringing more
widespread rain and keeping the pattern active.
&&
.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
A weak atmospheric river continues in Oregon, providing western
Washington with some widespread showers across the area this
afternoon. This weak atmospheric river will lift northward later
this evening and into Friday morning, allowing for more moisture
to funnel in the area, primarily south of Seattle, although
showers will still be present across much of the CWA. A Winter
Storm Warning continues for the Cascades and the Olympics as
significant mountain snow continues, on the order of a couple of feet
for Snoqualmie and Stevens Pass.
Turning into Friday morning, the forecast gets a bit complex and
complicated. Cooler air aloft will push down the snow levels
downwards to 500 to 1000 feet, which would allow a rain/snow mix
to develop across the region. There is usually the question
whether moisture will be present, and guidance does show some
moisture from the aforementioned atmospheric river still being
around the area (especially in the southern half of the state).
Latest guidance does suggest there could be light accumulations
possible on the higher foothills, along with grassy and elevated
surfaces. This is a complex situation as local surface
conditions and temperatures will be critical factors in what (if
any) snowfall accumulations may be present early Fri morning.
Overall: you will likely see snow in the interior (particularly
in Puget Sound) Friday morning in some capacity. However,
ground temperatures and near surface temperatures are likely to
be above freezing, which will result in highly variable surface
accumulation. The places that are likely to see any sort of snow
that sticks, are places on the higher foothills, which are
likely around an inch or two at best. The time frame for this is
generally early Fri morning, (4AM-9AM). After that, daytime
heating will take over and warm everything up. Shower will
decrease throughout the day, and high temps will be in the low
40s. Heavy mountain snow continuing.
The same problem exists for Saturday morning, although there
will be less moisture present across the area. Could see a few
flakes fly, but otherwise, Saturday will be a drier day with
temperatures in the mid 40s as an offshore ridge builds.
Mountain snow will also have gradually subsided by Saturday.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Ensembles continue to agree of a warm front will move over the
offshore ridge Sunday into Monday, which would bring another
round of precipitation over the area. Guidance continues to
depict the ridge not being strong enough to keep an atmospheric
river from the north out of our area, with lowland rain and a
unsettled pattern continuing throughout midweek. A warmer air
mass looks to bring up snow levels to 7000 to 8000 feet, along
with high temps creeping in the upper 50s, and even lower 60s.
Mazurkiewicz
&&
.AVIATION...
A strong upper level jet will lift northward, with a stationary
front to the south remaining over the WA/OR border. Showers will
continue to fall across the terminals through tomorrow, with
activity decreasing north to south through the day. Cooler
temperatures tonight may lead to some snow mixing in with the rain
showers. Probabilities of snow sticking on airport surfaces remains
low, though cooler and shady spots may see a few flakes stick
briefly overnight. Ceilings and visibilities will deteriorate
tonight into Thursday, trending from VFR down to MVFR and IFR.
Localized pockets of LIFR can`t be ruled out either. Breezy
southwest winds 8-12 kt with gusts to 20 kt will diminish to 5 kt
this evening, becoming variable under 5 kt tonight and switching to
a northerly direction during the day Friday (still under 5 kt). The
ensembles have ceilings improving towards MVFR late Friday.
KSEA...Light to moderate rain through tonight, with a chance of a
rain/snow mix overnight/early Friday morning. No snow accumulations
are expected for the terminal. MVFR ceilings/visibilities this
afternoon will likely decrease to IFR later tonight into Friday,
with MVFR likely late Friday afternoon/evening. Southwest winds 8-12
kt gusting to 18 kt will decrease to 5 kt tonight, becoming variable
late and switching to the northeast on Friday at or less than 5 kt.
HPR
&&
.MARINE...
A stationary front will remain over the southern coastal waters
through the weekend. Precipitation will continue to pass over the
waters, with reduced visibilities and ceilings at times. Winds will
continue to decrease through the afternoon from yesterday`s cold
front that passed through. A small craft advisory remains in effect
through 5 PM for the Strait of Juan de Fuca for lingering west winds
over 20 kt, and the coastal waters through 11 PM for seas above 10
ft. The winds will turn northerly on Friday, with a medium chance on
Saturday that gusts exceed 20 kt for the coastal waters. Seas
through the weekend will drop and hold around 6 to 8 ft, further
decreasing to 4 to 6 ft. A warm front will skirt the outer coastal
waters Monday next week, with potential for gusty south winds for
the coastal waters, and a few interior waterways. These winds are
forecasted to linger into late Tuesday. Seas on Monday will rise to
10 to 12 ft, and linger at those heights through midweek.
HPR
&&
.HYDROLOGY...
The Skokomish River has crested and will continue to linger in
Action Stage. More rain in the forecast through Friday will
keep the threat of flooding along the Skokomish Friday into
Saturday. With the heaviest precipitation over the Southwest
Interior there is also a threat of flooding Friday into the
weekend for a few rivers in the Chehalis Basin including but not
limited to the Skookumchuck, Newaukum and the Chehalis River
from Grand Mound to Grays Harbor. Therefore, a Flood Watch has
been issued for those following areas. The flooding threat will
ease Sunday into next week for the southern portion of the
area. Atmospheric river forecasted to move inland to the north
during the first part of next week. If the river ends up a
little further south rivers over the northern portion of the
area will bear watching the first part of next week.
Felton/Mazurkiewicz
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 5 AM PDT Saturday for Cascades of
Pierce and Lewis Counties-Cascades of Snohomish and
Northern King Counties-Cascades of Southern King County-
Cascades of Whatcom and Skagit Counties-Olympics.
Flood Watch from Friday morning through Sunday afternoon for
Cascades of Pierce and Lewis Counties-Foothills and
Valleys of Thurston and Lewis Counties-Foothills of the
Western and Southern Olympic Peninsula-Grays Harbor
County Coast-Lower Chehalis River Valley-Lowlands of
Lewis and Southern Thurston Counties-Middle Chehalis
River Valley-Olympia and Southern Puget Sound-Olympics-
Willapa and Black Hills.
PZ...Small Craft Advisory until 2 PM PDT this afternoon for
Admiralty Inlet-Grays Harbor Bar-Northern Inland Waters
Including The San Juan Islands-Puget Sound and Hood Canal.
Small Craft Advisory until 5 PM PDT this afternoon for Central
U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
Strait Of Juan De Fuca.
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.
&&
$$
NWS SEW Office Area Forecast Discussion