Brier Weather Station
Latitude N 47° 46' 49" Longitude W 122° 16' 48" Elevation 341 ft
000
FXUS66 KSEW 040033 CCA
AFDSEW
Area Forecast Discussion...CORRECTED
National Weather Service Seattle WA
433 PM PST Sun Dec 3 2023
.SYNOPSIS...An atmospheric river will impact the region Monday
through Tuesday, bringing periods of heavy rain to western
Washington and an increased risk of river flooding. An upper level
trough will cross the region late in the week for a shift toward
more showery precipitation, cooler temperatures, and lowering
snow levels. A brief break in the active pattern is possible on
Friday, before additional systems move through the region over the
weekend.
&&
.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Latest radar imagery
this afternoon shows some light shower activity persisting along
the coast and a convergence zone lingering along the King -
Snohomish county border. Overall, hi-res guidance is indicative
of the convergence zone lingering into the early evening hours
before dissipating. Elsewhere, expect shower activity to dissipate
into the evening for a brief lull in the weather in between
systems.
An atmospheric river is slated to impact the region Monday through
Tuesday. Moderate to heavy precipitation is expected to spread
northward across western Washington starting Monday morning as a
warm front lifts across the region. Snow levels will rise rapidly
to 7500-9000 feet through the morning hours as a result. The
trailing cold front then looks to stall offshore before making its
way across the region on Tuesday. The latest forecast calls for
48 hour rainfall totals between 12Z Monday and 12Z Wednesday
generally ranging from 1.5 to 3 inches for the interior lowlands,
3 to 5 inches along the coast, 5 to 9 inches along the Cascades,
and 7 to 10 inches across the Olympics. The combination of QPF and
runoff from rain falling on top of snow in higher elevations will
lead to sharp rises on area rivers and an increased risk of river
flooding across the region. See the hydro section below for more
details. In addition to rain, breezy to locally windy conditions
will develop across the region during the afternoon hours and
persist through Tuesday morning. Large waves along the coast will
build towards 20 feet on Tuesday and may run up further on area
beaches at times.
Heavier rain associated with the cold front will then gradually
sag southward into Oregon on Wednesday, though conditions look to
remain showery across western Washington. At this time, additional
rainfall amounts look to remain light, from a couple hundredths
of an inch to a few tenths. 14
.LONG TERM /THURSDAY THROUGH SUNDAY/...Deterministic models remain
in good agreement with an upper level trough shifting eastward
through W WA through the day Thursday, keeping precipitation in the
forecast into the long term. This system will eject Friday in favor
of some long-overdue upper level ridging. Enough lingering moisture
may present for some morning and early afternoon showers, but the
majority of the afternoon and evening will be dry. The side effect
of this ridging is that it will allow for continued cooling as
daytime highs slide solidly into the 40s and snow levels continue to
lower below pass levels. Deterministic models disagree by 6 or so
hours as to when on Saturday to bring the next frontal system into
the area, and while ensembles at this point in the forecast offer an
array of solutions, the ensemble mean suggests that while some rain
can be expected, amounts will be generally light. There are some
hints at some atmospheric river support to the back end of this
system during the day Sunday, but deterministic models disagree on
both placement /GFS favors W WA while ECMWF leans more toward W OR/
and strength /ECMWF shows the AR connections being tenuous at best/.
Ensembles however are not biting into this solution at all,
suggesting a general down turn in activity at the close of the
forecast period. Current forecast blend of models is currently
leaning slightly more favorably in the direction of wetter
solutions, but not convincingly so, doing little to shore up any
confidence for this time frame. 18
&&
.AVIATION...Westerly flow aloft as we`re currently in between
systems. The next disturbance is slated to move inland early Monday
morning with another shot of widespread rainfall. Mostly VFR out
there currently as we`re post-frontal. Terminals in and around the
PSCZ (KPWT and KBFI) are seeing MVFR ceilings but improvement should
be met by 01-02z. For this evening, widespread VFR is expected but
more MVFR to possibly IFR conditions are to rebound as the
aforementioned next shot of rain takes aim at western Washington by
Monday morning.
KSEA...VFR currently as a PSCZ lingers just north of the terminal
with MVFR ceilings. Hi-res guidance is indicating this feature
should remain north of the airfield so VFR should remain through
this evening but it will continue to be closely monitored. Southwest
winds 10 to 15 knots with gusts up to 20 knots should gradually
ease in magnitude overnight. MVFR cigs are favored to return Monday
morning however as widespread rainfall returns.
McMillian
&&
.MARINE...A series of frontal systems will make their way across the
waters Monday through Thursday. Winds in the inland waters have come
down to below Small Craft Advisory, and a lull in winds in expected
tonight. Therefore, all headlines have been cancelled for tonight.
Winds will again come up, first along the coast and in the Central
and East Strait of Juan de Fuca early Monday morning, then for the
rest of the coastal waters Monday afternoon. Confidence is highest
for gales along the coast and for the East Strait, but is less so
for the Northern Inland Waters--thus keeping the watch until the
next update. The Central Strait looks to avoid headlines Monday night
into Tuesday with the southerly winds along the Puget Sound into the
Strait of Georgia and tapering down along the coast. While a break
in wind headlines for the long term is expected, SCA conditions for
seas will likely remain along the coast into the end of the week.
Seas at 10 to 12 ft will rise to 15 to 17 ft on Monday before
reaching 18 to 20 ft Tuesday. Seas then will drop to around 10 ft by
Thursday and look to remain around 8-10 ft Friday and into the
weekend.
LH
&&
.HYDROLOGY...An atmospheric river will impact the region Monday
through Tuesday and looks to bring rainfall amounts of 7 to 10
inches in the Olympics, 6 to 9 inches in the Cascades, 3 to 5
inches along the coast and 1.5 to 3 inches to the interior
lowlands through early Wednesday. Snow levels will rise rapidly
across the region on Monday, topping out and generally ranging
between 8000 to 9000 feet by Monday afternoon. A Flood Watch
remains in effect for the area through late Wednesday night.
The combination of heavy precipitation and rising snow levels
will most likely result in river flooding on many rivers across
western Washington. Rivers currently look to reach flood stage
Monday night or Tuesday. Moderate to major flooding will be
possible on some of the bigger rivers like the Snoqualmie, Snohomish
and Skagit as well as the lower reaches of the Chehalis. While
flooding looks likely across the region, there remains a degree of
uncertainty in its scope and extent. This will depend largely on
the reaction of the area rivers from runoff produced from rain on
snow for river basins in higher elevations and the locations of
the heaviest bands of precipitation, so it will be important to
stay up to date on the latest forecast developments.
In addition to the river flooding, burn scars in the Cascades will
have to be monitored with the heavy precipitation forecast. Elevated
risks of landslide and debris flows will also be possible, especially
later Monday through much of Tuesday. 14/Felton
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through late Wednesday night for Admiralty Inlet
Area-Bellevue and Vicinity-Bremerton and Vicinity-Central
Coast-East Puget Sound Lowlands-Eastern Strait of Juan de
Fuca-Everett and Vicinity-Hood Canal Area-Lower Chehalis
Valley Area-North Coast-Olympics-San Juan County-Seattle
and Vicinity-Southwest Interior-Tacoma Area-West Slopes
North Cascades and Passes-West Slopes North Central
Cascades and Passes-West Slopes South Central Cascades and
Passes-Western Skagit County-Western Strait of Juan De Fuca-
Western Whatcom County.
PZ...Small Craft Advisory until 4 AM PST Tuesday for Grays Harbor Bar-
West Entrance U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 1 AM to 1 PM PST Monday for Central
U.S. Waters Strait Of Juan De Fuca.
Gale Warning from 1 AM Monday to 1 AM PST Tuesday for East
Entrance U.S. Waters Strait Of Juan De Fuca.
Gale Watch from Monday morning through late Monday night for
Northern Inland Waters Including The San Juan Islands.
Small Craft Advisory from 10 AM Monday to 4 AM PST Tuesday for
Admiralty Inlet.
Small Craft Advisory from 1 PM Monday to 4 AM PST Tuesday for
Puget Sound and Hood Canal.
Small Craft Advisory until 10 AM PST Monday 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.
Gale Warning from 10 AM Monday to 1 AM PST Tuesday 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