Washington State Forecast Discussion

Western Washington


798
FXUS66 KSEW 110440
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
840 PM PST Tue Dec 10 2024

.UPDATE...High clouds across much of Western Washington this
evening with an upper ridge across the Pacific Northwest. High
clouds are expected to limit the extent of fog tonight into
Wednesday morning. However, fog is likely to continue from Olympia
southwards into early Wednesday, with lower clouds and patchy fog
elsewhere into isolated portions of central Puget Sound. No major
forecast updates this evening.

&&

.SYNOPSIS...High pressure will maintain drier conditions across
western Washington into Wednesday. Rain chances increase Wednesday
night into Thursday as a weak disturbance moves through the area.
Another stronger system will move into the region Friday into the
weekend, bringing the potential for gusty winds, lowland rain, and
mountain snow. An active weather pattern will continue into early
next week as additional disturbances move across the region.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...High pressure will keep
conditions dry across western Washington tonight and through much
of the day Wednesday. A few areas of patchy fog will be possible
across the southern Sound again Wednesday morning, but do not
expect extent of fog to be widespread as more mid to high level
cloud cover continues to stream in overhead. Morning lows on
Wednesday will be in the in the mid to upper 30s and afternoon
high temperatures will be in the upper 40s to low 50s.

A weak system will then move across the region Wednesday night
into Thursday, bringing the next round of lowland rain and
mountain snow to western Washington. With most of the energy still
looking to move into northern California, expect overall
precipitation totals to remain rather light. With snow levels
generally hovering between 2500-3500 feet, expect snow
accumulations of 1-3 inches to be possible for the Cascade
passes.

Another, stronger system looks to approach the region Friday
night into Saturday. While there still remains some discrepancy
regarding the track of this low pressure system, this will bring
the potential for gusty winds, lowland rain, and more substantial
mountain snow.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The aforementioned system
will move into the region on Saturday, with winds looking to
increase late Friday into Saturday morning. At this time, NBM
probabilities are indicating roughly a 20-30 percent of wind
gusts of 40 mph or greater along the coast and for areas across
the North Interior. Wind will remain highly dependent on the
track of this low pressure system, so details will continue to be
refined as guidance comes into better agreement. In addition to
wind and precipitation, coastal flooding will need to monitored
throughout the weekend as astronomical tides peak this weekend
into early next week for coastal areas. With the potential
combination of a sub-1000 mb surface low, tides, and increased
surf activity, coastal flooding potential will continue to be
monitored closely.

Conditions look to remain active heading into early next week as
another disturbance looks to move into the region Sunday into
Monday and bring another round of lowland rain and mountain snow.
14

&&

.AVIATION...A transition to southwesterly flow aloft this evening as
an upper level ridge axis gradually moves eastward over W WA.
Surface winds at most terminals northerly at around 5-10 kts before
easing tonight to speeds generally less than 5 kts and direction
proving to be either variable or with an easterly component.
Southerly winds emerge by 12Z and remain that way into Wednesday
afternoon.

Most locations VFR at the time of this writing, although the SW
interior and OLM already seeing fog development with IFR conditions
in place. Patchy there now, becoming more consistent after 06-08Z.
The NE corner of the Olympic Peninsula also seeing IFR conditions,
and potential forecast issue is that if winds shift easterly, will
that impact CLM. At this time, given the light speeds expected as
well as the cloud cover overhead, leaning toward minimal impact, if
any at all. Elsewhere, while cigs will lower overnight to more mid-
level clouds, that should eliminate or at the very least seriously
restrict fog chances elsewhere. Mostly high clouds expected for late
Wednesday morning into the remainder of the TAF period.

KSEA...VFR conditions expected for the duration of the TAF period.
High clouds increasing will likely limit fog development near the
terminal. While models suggest a 15-20% chance of IFR/LIFR fog, that
is not enough confidence for TAF inclusion. Northerly winds 5 to 10
knots this evening, decreasing to 3 to 6 knots overnight. Direction
turns southerly Wednesday morning and afternoon while speeds remain
steady.

Mazurkiewicz/18

&&

.MARINE...A surface high pressure will gradually weaken over the
coastal waters tonight before a weak front slides over the area
waters into Wednesday. This front will split and weaken into
Thursday, but will bring some small craft southerlies and some
elevated seas above 10 feet.

A stronger system looks to cross over the coastal waters Saturday
into Sunday, bringing the potential for gale force winds
throughout the coastal waters. Seas look to also build upwards to
around 15 to 18 feet, with the highest seas being over the outer
coastal waters. The inner coastal waters will likely be around 14
to 16 feet, but still a little far out to nail down exact numbers.

Mazurkiewicz

&&

.HYDROLOGY...Next round of precipitation with a weak system
Thursday will only result in small rises on the rivers. A stronger
storm will set up along the coast over the weekend with potential to
bring more significant precipitation to the region. While area
rivers will rise only the Skokomish River is currently forecast to
potentially reach minor flood stage. There is still some uncertainty
in the precipitation amounts over the weekend. Conditions will
continue to be monitored. Another round of precipitation early next
week will follow on the heals of the weekend storm that, with QPFs
slightly lower but with at least the Skokomish River riding fairly
high and again at risk of flooding. Felton/JBB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 4 AM Wednesday to 4 AM PST Thursday
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.

&&