667
FXUS66 KSEW 222340
AFDSEW

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

.SYNOPSIS...A strong low pressure system offshore will continue to
produce showers across much of the coverage area this afternoon.
A slight risk of isolated thunderstorms remains along the Pacific
Coast this afternoon. Gusty southerly winds will pick up this
afternoon across the entire region, with the strongest winds along
the Pacific Coast, and the Northwest Interior. Winds will die down
this evening into tonight, with precipitation chances beginning
to dwindle next week as the low moves inland. Cooler air will
follow towards Thanksgiving.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...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...Southerly flow aloft with strong low pressure off the
coast, turning more southwesterly this evening as said low shifts
northward. Surface winds largely from the south /with some
variations to the east or west here and there/ with speeds on
average 15-20 kts...although higher at some terminals. Gusts showing
similar variability, however breezier spots seeing gusts between 30-
40 kts. Trend this evening is for these winds to gradually ease with
most gusts subsiding by 06Z.

Cigs over W WA largely VFR, although locations under precip could
see conditions degrade to MVFR at times. Although cigs will
gradually lower tonight and into Saturday morning, most locations
should remain VFR...although locations more prone to lower cigs will
likely dip down into MVFR and possibly IFR down at OLM. Lingering
shower activity Saturday may cause cigs to dip slightly, but
widespread VFR likely to persist.

KSEA...VFR conditions in place and likely to remain that way for the
TAF period, although showers may allow for brief periods of low-end
VFR to high-end MVFR cigs. Sufficient low-level moisture will cause
cigs to drop some overnight, but still expected to remain VFR.
Lingering showers Saturday may help facilitate this lowering.
Southerly winds still strong and gusty, ranging 18-22 kts sustained
this evening with gusts up to 35 kts possible. Will see this
gradually lower as the evening progresses with gusts likely wrapping
up around 06Z. Speeds generally ranging 8-12 kts tonight and the
remainder of the TAF period.

18

&&

.MARINE...A deep surface low will continue to shift north over the
coastal waters, allowing both seas and winds to gradually ease
tonight and Saturday. Timing still looks good on inherited headlines
and as such will make no adjustments, as winds and seas look to
maintain current headlines through at least 4 AM early Saturday
morning. Follow-up headlines to show the steady decline of these
conditions will likely be needed at least for the coastal waters and
perhaps the Strait...while most SCAs should be good to expire with
no follow-up. Winds and seas will continue to ease throughout the
weekend as this low weakens as it continues northward over the
offshore waters. 18

&&

.HYDROLOGY...The Skokomish River will stay within a foot of minor
flood stage through the weekend. Additional precipitation and
snow melt at higher elevations in the basin will contribute to
higher levels on the Skokomish and could bump the river up into
minor flood stage by Sunday. Thus, a flood watch for Mason County
remains in effect.

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

&&

.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 late tonight for Hood Canal Area-Lower
     Chehalis Valley Area-Olympics.

     High Surf Advisory until 10 PM PST this evening for Central
     Coast-North Coast.

PZ...Small Craft Advisory until 4 AM PST Saturday for Admiralty Inlet-
     Grays Harbor Bar-Puget Sound and Hood Canal.

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

     Storm 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.

&&

$$