000
FXUS66 KSEW 062304
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
304 PM PST Mon Dec 6 2021

.SYNOPSIS...Colder conditions will continue this week with
multiple systems making their way through the area. These will
bring lowland rain, mountain snow, and periods of breezy winds.
Light wintry precipitation is possible in the lowlands again
Thursday morning, with minor accumulations possible. Confidence is
increasing in active weather continuing into next weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Light showers continue
across the region this afternoon with precipitation across the
lowlands being all rain. The 22Z shows a warm front draped across
Western Washington at this hour, with KATX radar picking up on the
boundary hugging the north side of the Olympics and trailing back
across the Everett to Arlington area. Surface winds obs support
this positioning of the front, as winds are currently out of the
east in these areas. Warm air will continue to advect northward
through tonight, pushing the front further north. Light showers
will linger across portions of the area through the overnight
hours with weak lift in place across the region at low levels.
Expect temperatures to remain steady through the overnight hours,
with lows in the low 40s. Patchy fog will be likely through the
overnight hours, reducing visibilities at times through daybreak
Tuesday.

A bit of a break expected tomorrow as an E-W oriented shortwave
ridge axis crosses Western Washington during the day. Temperatures
will rise into the 50s for highs as a result. However, the break in
active weather will be short lived, as a quick moving front
approaches and brings lowland rain and mountain snow back to the
region by Wednesday.

As the front approaches, southerly winds will increase, with gusts
reaching 25 to 35 mph at times late Tuesday night into Wednesday
morning. Snow levels will lower from around 4000-5000 feet to below
2000 feet across the region Wednesday. The Cascade passes will
likely see 6 to 10 inches of new snow accumulation on Wednesday,
which will impact travel during the day and into Wednesday night. A
secondary upper level shortwave trough will reinforce the mean
trough over the northwest on Thursday, continuing persistent lowland
rain and mountain snow across the region. Cascade passes will likely
see another 6 to 12 inches of snow during the day Thursday. As of
now, it is not out of the questions that some lowland areas,
particularly those in Whatcom and Skagit Counties could see a mix of
rain and snow in a period period Thursday morning. That said,
accumulations dont looks likely at this time and would be dependent
on precipitation intensity and quicker cold air advection than what
is currently forecast. Nonetheless, probabilities at KBLI for at
least 0.1" of accumulation is currently around 40% in the afternoon
NBM data. Precipitation will taper Thursday evening into Thursday
night.

.LONG TERM /FRIDAY THROUGH MONDAY/...The next system will be
moving into Western Washington on Friday, bringing a return of
lowland rain and mountain snow to the region. A warm front looks
likely to push across the region on Friday, bringing an initial
shot of rain and mountain snow ahead of the main band of
precipitation associated with the system. Ensemble guidance has
been consistent in a longer fetch of moisture streaming into
Western Washington this weekend, driven by a potent, closed upper
level low that will eject out of the Gulf of Alaska. While there
remains some discrepancies regarding Low track and timing as of
this afternoon, once can expect a wet and active weekend ahead
weatherwise. One important detail to note - snow levels are
forecast to generally remain below 4000 feet through this event,
with the exception of the Central and Southern outer coast where
snow levels may approach 5000 feet. This will largely preclude any
flooding threat for Western Washington. That said, heavy mountain
snow will be is becoming a greater possibility at pass level with
each model suite run. Current probabilities has a around a 50%
chance for at least 12-24 inches of snow accumulation Saturday and
Sunday at Snoqualmie and Stevens Passes. Anyone with travel
interests across the passes will want to stay tuned to the
forecast over the next several days as Mean trough will persist
over the region into early next week, keeping wet and stormy
weather in place for the region.

Pullin

&&

.AVIATION...A warm front is over the region and most of the precip
continues to be south of the area this afternoon. Still, drippy
weather with a few areas of light rain or drizzle and low cigs will
persist into the evening. The mountains and hills are obscured and
in many areas cigs are down on the deck. Perhaps on Tuesday Western
Washington will get some drier air behind the warm front.

KSEA...Warm fronts are the worst and it looks like the low cig will
drag on through the evening hours. We will see if there is anything
like a warm frontal passage with cigs lifting later tonight and
Tuesday morning.

19

&&

.MARINE...A warm front is dissipating over Western Washington this
evening. There are still southeast winds over the northern portion
of the coastal waters, but the lighter southwest wind is very slowly
working in toward the north coast. Tuesday will be a lackluster day
and then later Tuesday into Wednesday stronger onshore flow
develops as a cold front arrives. We might see westerly gales
develop in the Strait of Juan de Fuca behind the cold front on Wed.
Onshore flow persists into Thursday and then another vigorous
system will probably reach the area late in the week.

19

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 9 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.

&&

$$

www.weather.gov/seattle

NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather