307
FXUS66 KSEW 050433
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
833 PM PST Wed Dec 4 2024

.UPDATE...Areas of fog have developed tonight across Puget Sound
due to continued abundant moisture at the surface. A Dense Fog
Advisory has been issued for the majority of the interior through
Thursday morning. Of note, south to southeast winds will slowly
increase for localized areas into Thursday morning, which may
allow for some improvements in the dense fog, but not expected to
be widespread. Otherwise, temperatures tonight will be in the
30s, and localized upper 20s.

&&

.SYNOPSIS...Areas of dense fog will remain tonight into tomorrow
morning. A weak front will move through Thursday but will fall
apart before arriving. A more substantial frontal system will move
through Friday into this weekend, bringing more significant
rainfall and breezy winds. A brief period of dry conditions will
follow Sunday night into Monday before the active pattern
continues by mid-week.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Areas of patchy fog have
largely risen to become low stratus where it remains, mostly over
portions of the southern half of the interior, between Whidbey
Island and Olympia. Elsewhere, skies are clear. Temperatures range
from the mid 30s to the mid 40s, depending on how long clear skies
have persisted today. Areas of fog and freezing fog may redevelop
in the most prone areas again tonight into tomorrow morning,
particularly over the Kitsap Peninsula and the South Sound area,
where it may become dense at times. Lows tonight will be in the
low to mid 30s.

Clouds will increase tomorrow morning as a cold front moves
towards the area from offshore. This front is expected to rapidly
weaken as it approaches the area. Some light rain/drizzle is
possible along the Pacific Coast, otherwise most of western
Washington should remain dry. Enough wind and boundary layer
mixing should prevent widespread fog development and persistence
on Thursday. With less fog expected tomorrow, temperatures should
increase for Friday, with highs in the upper 40s and lows in the
upper 30s to near 40.

The ridge aloft that has been persistent over the area will begin
to deamplify and move east on Friday, being replaced by a large
upper-level closed low that will move across the area this
weekend. Chances for rain will begin along the Pacific coast
Friday morning as a surface warm front moves in, moving inland
Friday afternoon then followed by a cold front moving across the
area Friday night into Saturday, with showers persisting behind
the front throughout the day on Saturday. Snow levels will rise up
to 8-9,000 ft, before beginning to fall to around 3,500 ft by
Saturday night. 2 to 3 inches of rain will be possible over the
Olympic Peninsula and the North Cascades, with up to around 1 inch
for most of the lowlands. Winds will also be breezy across the
area as the front moves through Friday night into Saturday,
through currently looks to be well below advisory criteria.
Temperatures will warm up following the warm front on Friday and
Saturday, with highs in the low to mid 50s and lows in the mid to
upper 40s.

.LONG TERM /MONDAY THROUGH THURSDAY/...By Sunday, snow levels
will lower to around 3000 ft. Continued shower activity late
Saturday night into Sunday will allow for several inches of
accumulating snow over the passes during this period. Temperatures
will also cool, with highs Sunday back in the upper 40s and lows
in the upper 30s. Building waves along the Pacific coast Saturday
night into Sunday may bring high surf conditions. The upper level
low will depart Sunday night, being replaced by a brief ridge for
a period of dry conditions Sunday night into Monday before
additional systems look to impact the area by mid-week next week,
through details of the pattern evolution remain uncertain by that
point. Temperatures remain around the climatological normal, with
highs in the upper 40s and lows in the upper 30s.

62

&&

.AVIATION...Fog has once again settled over majority of Puget
Sound, with most terminals experiencing LIFR to IFR conditions.
Freezing fog may be possible locally in certain spots, but most of
the area currently has temps above freezing. Fog will likely stick
around throughout the overnight hours into Thursday morning,
before increasing mid level clouds start to spread across the
region ahead of weak front. Fog looks to start to scatter around
21-23z as these high clouds begin to move in.

KSEA...Another round of fog has developed this evening at the
terminal, with LIFR conditions. Winds have been noticeably gusty
at the terminal over the last hour, but will be likely short-
lived. Temperatures will be right around the freezing mark, with
freezing fog possible at times overnight. Fog will likely linger
through the morning before scattering out around 21z, as
increasing mid and high clouds will arrive ahead of a week front.
Surface winds predominantly southerly or southeasterly and
into Thursday.

&&

.MARINE...High pressure still across the waters today with
generally light winds. A weak front will approach the coastal waters
Thursday. There remains some potential (around a 40% chance) for
some wind gusts to 25 kt over the outer coastal waters as this front
approaches and falls apart, but not enough likelihood to issue a small
craft advisory for this system.

A stronger front on Friday is more likely to bring advisory strength
winds to the coastal waters (as well as the eastern Strait of Juan
de Fuca). These southerly winds will allow for steep seas to develop
across the coastal waters on Friday. Winds will switch to westerly
in the wake of the frontal system on Saturday, but will remain
breezy across the coastal waters and along the Strait of Juan de
Fuca as the associated low pressure system pushes inland over BC/WA.
Seas will build towards 15-18 ft across the coastal waters on Sunday
as a larger wave group arrives from the west. High pressure then
returns early next week with light winds and gradually subsiding
seas. Another disturbance may bring an end of the this lull around
midweek. Cullen

&&

.HYDROLOGY...An upper ridge over western WA will slowly move
east by Thursday, allowing a weak trough to move through. This will
bring, at best, a few light showers. Another weather system Friday
into Saturday is forecast to bring heavier precipitation. In
addition, snow levels are expected to rise later Friday into early
Saturday to 7000 to 9000 feet. This, combined with rainfall, will
result in rises on rivers across western Washington. The amount of
precipitation expected remains quite uncertain with the upper
amount 3 to 5 inches in the mountains, but only 2 to 3 inches
might be more likely.

At this time, the Skokomish River is the main river of concern for
potential river flooding during this period, and even that would
take something more than the lower end of the precipitation range.
The heavier precipitation amounts could drive some rivers to close
to or over minor flood. Due to this and the higher snow levels
Friday into Saturday, other area rivers will need to be monitored
for flood potential as well.

JBB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Dense Fog Advisory until 10 AM PST Thursday for Admiralty Inlet
     Area-Bremerton and Vicinity-Everett and Vicinity-Hood Canal
     Area-Seattle and Vicinity-Southwest Interior-Tacoma Area-
     Western Skagit County-Western Whatcom County.

PZ...None.
&&

$$