FXUS66 KSEW 221701
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
901 AM PST Thu Feb 22 2024

.UPDATE...An offshore low will continue to dissipate today,
allowing conditions to dry out. Ridging will amplify northward
into Washington and allow temperatures to warm up as skies
continue to clear. Temperatures are on track to peak in the mid
50s across the lowlands today and tomorrow. The main event of the
forecast period continues to be an incoming storm system on
Sunday, which will bring in heavy mountain snow, breezy winds, and
cooler conditions.

&&

.SYNOPSIS...An upper low offshore will weaken today with ridging
building into the Pacific Northwest. Drier weather later today
through Friday. A system north of the area will bring increasing
precipitation Saturday. A stronger front on Sunday will bring
breezy winds, lowland rain, and heavy mountain snow. A cooler,
active pattern expected next week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...An upper low offshore
continues to bring showers across western Washington, although
conditions will continue to slowly dry through this morning,
especially for southern areas. The best chance for rain showers
into this afternoon will be along the Olympic Peninsula, but in
general drier weather is expected for most of the area due to
ridging building into western Washington. This ridging will also
allow for clouds to clear for most areas later this afternoon for
some sunshine. Dry weather tonight through Friday with the
ridging. This will promote fog development tonight into Friday
morning, especially for fog prone areas across the Southwest
Interior, with some stratus near Puget Sound. Otherwise, a mix of
clouds and sunshine on Friday with highs in the 50s.

The ridge will flatten on Saturday as a system north of the area
begins to bring precipitation to portions of western Washington.
The best chance for lighter rain on Saturday will be King County
northward, especially over the Cascades, and across the Olympic
Peninsula. Temperatures will be slightly cooler on Saturday due to
the increased cloud cover and rain potential with highs in the
upper 40s to low 50s.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...A more active weather
pattern is expected Sunday into next week as troughing slides
southward from British Columbia and into the Pacific Northwest. A
frontal system on Sunday will bring increasing heavier rain for
the lowlands, breezy winds, and heavy mountain snow. Snow levels
initially ranging 3000-4000 feet on Sunday will fall towards 1000
feet by Sunday night. A period of rain/snow mix may occur at the
onset of precipitation for Snoqualmie Pass, with snow for Stevens
Pass. Snowfall amounts on the NBM range from 12-24 inches for the
Cascade Passes (heaviest for Stevens Pass) during the 48 hours
period ending 0400 Tuesday morning, with the heaviest snow
expected Sunday into Sunday night.

The upper trough will move over western Washington on Monday for
cold air aloft and post-frontal onshore flow. Convective showers
will be around on Monday. Given the colder air aloft, snow levels
will likely drop towards the surface, particularly in heavier
showers, allowing for snow or rain/snow mix for areas of the
lowlands. Given the convective nature of the showers, it will be
hard to pinpoint the exact location of any rain/snow mix at this
time, but a favored area late Sunday night into Monday morning
looks to be any convergence that develops in the vicinity of
Snohomish County. With that said, given high temperatures in the
40s, any lowland snow accumulations on grassy or elevated surfaces
will melt quickly. Showers look to continue into Tuesday with
slight warming in temperatures. Ensembles then suggest another
system bringing additional precipitation later Tuesday into
Wednesday for western Washington. Overall, a cooler and wetter
weather pattern is expected for much of next week. JD

&&

.AVIATION...Weak upper ridging will build into the region today with
light west to northwest flow aloft. Predominant VFR conditions
expected across the area today after areas of low clouds dissipate
by 18Z. Light surface flow, clearing skies, and remnant low level
moisture will lead to areas of IFR/LIFR in stratus/fog especially
south Puget Sound and Southwest Interior 10Z to 18Z Friday morning.

KSEA...VFR through late tonight. Moderate confidence that IFR
stratus will form in the vicinity of the terminal 12Z-18Z Friday.
Surface winds light southerly will transition to N/NE 4 to 7 knots
by 00Z and continue overnight. 27

&&

.MARINE...Surface ridging will build into the coastal and offshore
waters today into tonight. The ridge will weaken on Friday in
response to a trough and associated frontal system moving into the
British Columbia coast Friday night into Saturday. A deepening
trough over the Gulf of Alaska will push a vigorous frontal system
across the waters on Sunday. Strong post-frontal onshore flow on
Sunday will likely lead to headlines for most of the waters with
possible gales for the coastal waters as well as in/near the strait.

Coastal seas will build well into the double digits by Sunday and
remain hazardous through the early portion of next week. 27

&&

.HYDROLOGY...Rainfall over the Olympics has tapered off this
morning, and the Skokomish river is cresting, with levels expected
to decrease through the morning. The flood watch for Mason county
will remain in effect for the next few hours, but will be cancelled
soon as the river is not expected to rise into minor flood stage. No
other area rivers are experiencing rises.

Kristell

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through this evening for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

PZ...None.
&&

$$