803
FXUS66 KSEW 161616
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
916 AM PDT Mon Mar 16 2026
.SYNOPSIS...An atmospheric river will impact the region through
much of the week, bringing multiple rounds of rain and warmer
temperatures to western Washington. Higher snow levels and
periods of moderate to heavy rain will bring rises to area
rivers this week, with river flooding possible. Wet and
unsettled conditions look to continue into next weekend as
another system moves into the region.
&&
.SHORT TERM /TODAY THROUGH WEDNESDAY/...The Winter Weather
Advisory in the north Cascades has ended. Snow levels are rising
over 8,000 ft today for main rain in the mountains. The focus
will turn toward possible river flooding due to rain and
snowmelt runoff, particularly toward the latter half of the
week. 33
Previous discussion...A warm front offshore, associated with
an atmospheric river aimed at British Columbia, will continue to
stream precipitation into western Washington this morning. Snow
continues to fall across portions of the Central and North
Cascades early today, but expect a gradual transition over to
rain as conditions warm and snow levels rise to 8000-10000 ft.
Latest observations indicate that snow has already transitioned
over to rain at Snoqualmie Pass early this morning, so have
allowed for the Winter Weather Advisory to expire for the
Central Cascades. With snow levels being the last to rise across
the Northern Cascades, have maintained the Winter Weather
Advisory for the Cascades of Skagit and Whatcom counties through
mid morning. Precipitation will continue through the morning
hours as the front lifts across the area. A brief break is
expected this afternoon and early evening in the wake of the
front before the moisture axis over British Columbia gradually
sinks southward and brings the next round of rain to the area
tonight into Tuesday. Temperatures will be warm and mild across
the region today, with afternoon highs expected to be in the 50s
to low 60s (across the southern Sound). Conditions will be
breezy at times today into Tuesday, with wind gusts to 25-35 mph
possible. Breeziest spots will be areas along the coast and
across the North Interior.
Another round of widespread rain will spread over the area on
Tuesday as the moisture axis of the atmospheric river gradually
sinks southward across the area. Periods of rain will continue
into Wednesday as the axis remains positioned over the region.
For western Washington, the highest QPF remains concentrated
across the northern two-thirds of the region (primarily along
the Coast, Olympics, and the Cascades from King County northward).
Rises will occur on area rivers, with the main concern throughout
the week being potential hydrological impacts from higher snow
levels and from rain falling on recent snow in the mountains.
For more info on river flooding, see the hydrology section below.
Temperatures will remain warm and mild Tuesday and Wednesday,
with afternoon highs expected to be in the 50s and overnight
lows expected to be in the upper 40s to low 50s.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
The warm and wet pattern will persist through much of week, with
additional periods of rain expected through Friday before the
plume of moisture pushes southward. The heaviest precipitation
will remain focused across the Cascades from King County northward,
across the Olympics, and along the Pacific Coast for the second
half of the week. Ensembles then hint at a cooler trend commencing
next weekend as the atmospheric river exits the area and another
system moves in from the northeastern Pacific. While there is
still some disagreement to just how wet and cool conditions
will get over the weekend, snow levels look to drop back down
between 2000-3000 ft. Afternoon highs over the weekend will be
in the 50s, but overnight lows look to drop back into the 30s.
14
&&
.AVIATION...Scattered showers will continue today, as FROPA
cause wind speeds to pick up for the second half of the TAF
period. Areas generally from KSEA north will see speeds between
10-15 kts by this afternoon. Cigs will see some improvement as
well, with VFR conditions returning. This FROPA will allow for a
brief break in rain, but rain returns tonight as the frontal
boundary sags south into western WA, bringing more MVFR
conditions.
KSEA...VFR/MVFR at the terminal so far this morning. More rain is
pushing inland, and -RA will return after 17Z, lingering into the
afternoon. As the front moves through, expect southerly winds to
increase to 8-10 kts after 17Z, lingering until around 00Z-02Z.
After the rain is forecast to end or become more isolated after 20Z,
MVFR cigs should return to VFR. VCSH returning after 04Z this
evening, though conditions look to remain VFR at this time.
21/41
&&
.MARINE...Southerly flow will increase over the waters today as
a warm front lifts north into B.C. Seas will remain elevated
through Tuesday. Southerly flow will prevail through Thursday
generally within 10-20 kt range. Grays Harbor Bar conditions
will be close to SCA criteria come Tuesday as the seas approach
ten feet. For the Small Craft conditions in Puget Sound, expect
the more elevated winds to occur from Seattle north. For the
southern Puget Sound, winds will be slightly less than in the
aforementioned areas.
21
&&
.HYDROLOGY...River flooding continues for the Chehalis River at
Porter, which is currently cresting and expected to recede
today, before falling below flood stage this afternoon.
An atmospheric river impacting the region this week will bring
additional flooding concerns as it brings periods of moderate
to heavy rain to western Washington. While the bulk of the
moisture will initially be focused on British Columbia today,
it will gradually sink southward into our area on Tuesday and
remain over the region through much of the week. Highest QPF
amounts will remain focused on the coast, the Olympics, and the
central and northern Cascades. The combination of higher snow
levels and rain on recent snows in the mountains will lead to
rises on area rivers, especially those flowing off the central
and northern Cascades. Rivers will continue to run high through
the end of the week, before receding over the weekend.
14
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from Tuesday afternoon through Wednesday afternoon
for Foothills of the Western and Southern Olympic
Peninsula-Middle Chehalis River Valley-Olympia and
Southern Puget Sound-Olympics-Southern Hood Canal-Willapa
and Black Hills.
PZ...Small Craft Advisory until 5 AM PDT Tuesday for Admiralty
Inlet-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-
East Entrance U.S. Waters Strait Of Juan De Fuca-Northern
Inland Waters Including The San Juan Islands-Puget Sound
and Hood Canal-West Entrance U.S. Waters Strait Of Juan
De Fuca.
&&
$$
NWS SEW Office Area Forecast Discussion