149
FXUS66 KSEW 091643
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
843 AM PST Sat Nov 9 2024

SYNOPSIS...A front will cross western WA this afternoon for a
wet period of weather. Active weather will continue into early
next week, with more lowland rain, mountain snow, chances of
thunder, high surf and breezy conditions.

&&

SHORT TERM /TODAY THROUGH MONDAY/...A wet day ahead with a slow-
moving front cross the region. Most areas will see 0.25-0.75"
rainfall through this evening. Temperatures in the lower to mid
50s this afternoon - just a few degrees warmer than current
readings. 33

Previous discussion...Recent radar imagery depicts a front
training over the coast, with rain spreading through Forks and
Quillayute. This front will start to move inland throughout the
morning, with rain spreading through most of the interior.
Precipitation isn`t all that impressive compared to what we will
see later on in the week, with amounts of 0.25-0.75" across the
lowlands. Temperatures today will be rather stagnant, in the mid
50s across most of the area.

A brief break in rainfall tonight into Sunday morning, before a
robust frontal system dips down south from British Columbia and
enters western Washington by Sunday night. Periods of moderate to
at times heavy rainfall can be expected into Monday. Most of the
rainfall will be focused over the coast, Olympics, and Cascades.
For this particular system, rainfall totals generally range
anywhere from 2-3" in the Cascades, 3-4" in the Olympics, and
around 1-1.5" in the lowlands. Rivers will start to rise with the
increase in precipitation, especially the Skokomish River where
there is a potential for flooding. A Flood Watch continues for
Mason County, largely due to the Skokomish River. Refer to the
Hydrology section below for details on possible river flooding.
Along with the rain, the air mass will be slightly unstable
resulting in chances of thunderstorms mainly along the coast. Snow
levels will initially be around 5000-6500 feet Sunday night
before falling generally around 3500-4000 feet later Monday night.
Snowfall will largely be limited to the higher elevations on
Sunday, but as snow levels fall to 3500-4000 by Monday night,
could see some accumulating snowfall above 3500 feet affecting the
higher mountain peaks and passes. In addition, high surf is
possible along the coastline Monday night into Tuesday, with 15 to
18 feet seas, even possibly 20+ foot seas in the outer coastal
waters.

LONG TERM /TUESDAY THROUGH FRIDAY/...A stronger system will
approach the area Tuesday night into Wednesday for another batch
of lowland rain, mountain snow, thunderstorms, and breezy
conditions. The increased amount of precipitation will definitely
contribute to keeping the rivers running high, with the
possibility of additional rivers going into Action stage, and
possibly minor flood stage. Another round of snow in the
Cascades, with accumulating snow above 3500 feet as snow levels
will largely remain 3500 to 4000 feet on Tuesday. Passes such as
Washington Pass and Stevens Pass will likely see accumulations.
There is some uncertainty regarding amounts, with snow levels
quickly rising back up on Wednesday back up to 5000-6000 feet.
Thunderstorm chances will also return particularly along coastal
locations, with breezy conditions across most of the interior.

Additional troughing offshore will keep unsettled weather through
the end of the week, with more rain and mountain snow.

Mazurkiewicz

&&

AVIATION...A weak front continues to very slowly advance across the
region. This has maintained some light rain and lower ceilings
across the northwest portions of the area, extending from around
KBLI southwest through KHQM. Ceilings elsewhere will continue to
gradually lower as the front moves through, but expect predominantly
VFR ceilings through the interior Puget Sound terminals through
daybreak. Chances for MVFR ceilings inland increase as rain
associated with the front becomes more widespread by the late
morning and early afternoon. Models suggest that MVFR to IFR
conditions will becoming increasingly widespread late in the
afternoon as ceilings and visibilities lower in the rainfall.
Decreasing rain late evening, but expect widespread lower
ceilings to result overnight tonight.

KSEA...VFR ceilings continue early this morning but will
continue to lower as the front approaches. Expect MVFR
cigs/visibility later today in rain. Wind remains predominantly
southerly through the period.

&&

MARINE...A front remains across the waters early this morning, with
seas building to around 8 to 11 feet over the coastal waters and
into the western Strait of Juan de Fuca. The small craft advisory
for these zones remains in effect through the day today. Winds
haven`t been particularly strong with this weak front, but will
shift to become predominantly northwest behind the front by tonight.

Seas may briefly subside to 7-9 ft Saturday night into Sunday, but
the next front will quickly approach and bring building seas as well
as stronger winds across the waters. Expect solid small craft winds
across most zones, and the potential for gale gusts (and local
sustained gales) over the coastal waters and near the eastern Strait
of Juan de Fuca. With latest probabilistic guidance continuing to
suggest around a 50% chance for gale gusts, a gale watch has been
issued for these zones. Seas will again build above 10 ft by late
Sunday and will sharply build to around 20 ft over the coastal
waters around Monday. A stronger front around Tuesday will bring a
better chance of more widespread gales.

&&

HYDROLOGY...A weakening frontal system will move through Western
Washington this afternoon for increasing rain, although at this
time QPF amounts are expected to remain on the light side compared
to what we will see later on in the week.

A more significant chance of precipitation is expected Sunday
through Monday, and again on Wednesday as an active weather
pattern returns with weak to potentially moderately strong
atmospheric river events coming through the area. The
precipitation amounts will be strongly orographically influenced
with precipitation totals in the mountains expected to be 3 to 5
inches for both storms except locally over 6 inches on the
Olympics for the last one (Wednesday).

The succession of storms will increasingly build up soil moisture
and river levels throughout this period which will increase the
possibility for river flooding. Snow levels vary generally from
4000 to 6000 feet which will impact precipitation type and affect
the amount of storm runoff.

At this time, the Skokomish River is the only river forecasted to
rise into flood stage, and potentially into moderate flood stage
during the middle of next week. For other rivers, significant
rises are expected with several river forecast points above Action
Stage, and flooding could be possible, but at this time is not
forecasted. The Hydrologic Ensemble Prediction System (HEFS),
though typically too low of probabilities for any one time point,
has some elevated probabilities for the 10 day period. For
example, it has a 51% chance for minor flooding for the Snoqualmie
River near Carnation. Flooding extent will depend on rainfall
rates, temperatures, as well as snow levels with precipitation
that falls with each of these weather systems next week. We will
continue to assess the hydrologic conditions and forecasts for any
additional areas of potential flooding.

Bower/JD/Mazurkiewicz

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from Sunday evening through late Monday night for
     Hood Canal Area-Lower Chehalis Valley Area-Olympics.

PZ...Small Craft Advisory until 7 PM PST 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-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Gale Watch from Sunday afternoon through late Sunday night for
     East Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Sunday afternoon through Sunday 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.

&&

$$