466
FXUS66 KSEW 230445
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
845 PM PST Fri Nov 22 2024

.SYNOPSIS...A broad area of low pressure will remain offshore into
the coming weekend for continued unsettled conditions. A trend
toward colder and drier conditions is expected next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Showers continue to rotate
onshore this evening, but winds will gradually ease as the
surface low just offshore of Vancouver Island slowly drifts toward
the northwest and weakens. Broad troughing will remain offshore
through the upcoming weekend for showery periods and temperatures
near or slightly below seasonal norms. Ensembles this evening are
continuing to advertise a noted shift toward colder and drier
conditions as we approach the Thanksgiving holiday. No significant
updates were made to public forecast this evening, but portions of
the aviation, marine, and Skokomish River forecasts were updated and
noted in the discussion below. 27

The strong upper level low that has been impacting our region the
past couple days has moved closer to the Washington Coast this
afternoon. The center of the low is visible on satellite still, with
rotation visible around 100 miles west of Cape Elizabeth. Radar has
been active late this morning and afternoon with an associated
occluded front off the coast. The warm air that moved in this
morning from the warm front to the south added some instability for
thunderstorms off the coast, and along the coast. The ingredients
will still remain for an isolated threat of thunder this afternoon,
but otherwise the threat will decrease slightly going through
tonight, and continue into Saturday. Couple strong storms may be
able to produce small hail and gusty winds. For all remaining areas,
showers will continue this afternoon and begin to taper back
Saturday.

Gusty winds remain the primary concern with this system going into
this afternoon and evening. Winds have begun to pick up out of the
south along the coast this afternoon, with gusts observed up to
60 mph in Hoquiam and La Push. Higher gusts have also been
observed coming through Olympia with gusts up to 53 mph. With the
southerly winds coming in on the hotter side of the ensemble
models, the wind advisory for the North Coast and Central Coast
has been upgraded to a high wind warning through tonight, and the
wind advisory has been expanded for all of the interior and Puget
Sound until 6 pm this evening (including Seattle, Everett,
Bremerton, Tacoma, and Olympia areas). Again it will be a short
window of gusty winds this afternoon and early evening, with winds
beginning to diminish going into this evening and into tonight,
and this system is not expected to produce as many impacts as the
Tuesday/Wednesday system. Additionally, a high surf advisory also
remains in effect for the coast through this evening, with waves
of 20 to 24 feet expected along beaches.

Moving further into the weekend, the upper low will begin to
split, with one trough moving inland into south-central Canada,
and the primary low remaining offshore. The best chance of
precipitation Saturday will be west of the Olympics, where there
will likely be more organized bands of showers (and isolated
thunderstorms). Remaining areas will still see shower activity
through Saturday and into Sunday. By Sunday morning, precipitation
from Friday into Sunday morning is expected to reach 1-2 inches
along the coast (2-3 inches in the Olympics), a quarter to half an
inch in the lowlands/interior, and Cascades. Snow totals will be
lower (due to the high snow levels Friday), but a slushy 1-2
inches of snow is possible at Snoqualmie and Stevens Pass
(heaviest accumulations on high mountain peaks). The precipitation
chances begin to dwindle on Monday as the low is expected to
completely to move inland later in the day.

.LONG TERM /TUESDAY THROUGH FRIDAY/...As previously mentioned,
expectation remains that the upper level low offshore will move
southeastward into Oregon by Tuesday. The trough/low will bring
northwest flow aloft behind, and as a result, much of the region
will see cooler temperatures, with highs in the lowlands dropping
into the mid 40s towards Thanksgiving, and lows in the low to mid
30s. The NBM did keep some slight pops during this period at around
20 to 30 percent (would not be surprised if the pops disappear in
future forecasts), but the cold air overnight would be enough to
potentially produce some snow flurries (bout a 15% chance) with
any light rain showers that do develop in the dark. The Bellingham
area would be the most likely place to see the snowflakes mix in
with the showers, but potentially it could spread into portions of
the lowlands come Thanksgiving time. Check back for updates this
weekend and next week for updates on this.

HPR

&&

.AVIATION...Upper level troughing will remain just offshore into
Saturday producing southwesterly flow aloft over Western Washington.
Gusty surface winds this evening will ease toward morning as a deep
surface low offshore gradually pulls away and weakens. As
the atmosphere stabilizes and winds ease, localized areas of MVFR or
IFR ceilings may form toward morning. Predominantly VFR ceilings
with a few showers in the area are expected for Saturday afternoon.

KSEA...Ceilings expected to remain largely at or above 035-040 this
evening with a few showers in the area. Shower activity diminishes
overnight and ceilings may drop to high end MVFR for a brief period
Saturday morning. Gusty southerly surface winds will ease to 6 to 10
knots overnight.  27

&&

.MARINE...A 983 millibar surface low west of Vancouver
Island will continue to gradually weaken into Saturday as it
drifts slowly toward the northwest. This will allow both winds
and seas to gradually subside. Headlines were adjusted for
some of the waters this evening to account for easing winds.
The low will fill and drift in the Oregon coastal waters early next
week as surface ridging builds over the interior of British Columbia.
This will introduce a welcome quieter period across area waters with
winds and seas falling below headline thresholds Tuesday into the
beginning of the upcoming holiday.  27

&&

.HYDROLOGY...A flood warning for the Skokomish River was issued this
evening as continued showers over the Olympics and higher snow
levels brought a steady rise to the river. The river is expected to
dip below flood stage again on Saturday morning, but will be
monitored as it is expected to remain within a foot or so of flood
stage through the weekend.

For the remainder of the rivers no flooding is expected at this
time. Lower snow levels into the weekend in the Cascades will
limit runoff and reduce any flooding chances for rivers flowing
off the Cascades. Precipitation for the remainder of the period
will come in bursts. This combined with snow levels remaining
relatively low will keep rivers in their banks. 14/27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory until 4 AM PST Saturday for Admiralty Inlet Area-
     Central Coast-North Coast-San Juan County-Western Skagit
     County-Western Whatcom County.

     Flood Watch through Saturday afternoon for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

PZ...Small Craft Advisory until 4 AM PST Saturday for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca-Grays Harbor Bar-
     Puget Sound and Hood Canal-West Entrance U.S. Waters Strait
     Of Juan De Fuca.

     Gale Warning until 4 AM PST Saturday 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-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

&&

$$