996
FXUS66 KSEW 192153
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
253 PM PDT Thu Sep 19 2024

.SYNOPSIS...Weak high pressure remains in place for the next few
days with a few passing disturbances and weakening fronts bringing
some deeper marine clouds and cooler temperatures at times through
the weekend. Stronger high pressure may build and bring some light
offshore flow early next week, bringing temperatures back above
normal.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Another dry day with clouds
scattering out again this afternoon as weak onshore flow
continues. A weak disturbance may induce a few light showers in
portions of the interior (especially toward the Cascades) on
Friday, but most areas will stay dry and some additional cloud
cover (and resulting cooling in temperatures) will remain the most
notable impact to sensible weather. Yet another front approaches
and likely fades away as it stalls over British Columbia, again
leaving most of western Washington dry. Temperatures trend a
little warmer into Saturday as a result, making it closer to
seasonal normals. Sunday will likely be a return to cloudy cool
and somewhat wetter across the region as the next front is likely
able to hold together better and bring some additional moisture.
While ensembles still have a fair amount of variability with this
system, we`re likely to see rainfall in the one quarter to half
inch range near the coast and in the mountains (especially to the
north). Confidence remains lower in the lowlands of the Puget
Sound region and especially south along I-5 through Lewis County.

.LONG TERM /MONDAY THROUGH THURSDAY/...Ensemble guidance has
consolidate to favor a building ridge across the western U.S.
early next week, which would support warming temperatures and
decreasing cloud cover. This could bring temperatures back into
the mid to upper 70s through much of the interior, with the
warmest locations approaching 80. Offshore low-level flow would
likely bring this warming to the coast as well, as the sea-breeze
will be limited or eliminated. Fortunately the antecedent
moisture will likely hinder any significant fire weather concerns,
but will need to continue to monitor the evolution of the
pattern. The ridge likely breaks down by Wednesday or Thursday,
again opening the door for cooler temperatures and increasing
clouds and rain chances. That said, spread in the ensemble
guidance does increase once again in this time period and forecast
confidence decreases again. Cullen

&&

.AVIATION...Flow aloft will increase out of a northwest as trough
moves out of B.C. Canada eastward, and as ridging moves in from the
Pacific. Low clouds from this morning are scattering out to VFR
across nearly all terminals this afternoon (with a few MVFR cloud
decks holding around Hoquiam, Arlington to Whidbey Island, and
Shelton that will continue to improve to VFR). Mix of cumulus and
pockets of altostratus/cirrus will remain going into the evening.
The next marine push overnight/Friday morning will bring widespread
MVFR stratus across western WA, with the higher chance of IFR/LIFR
CIGs in the Cascades, and areas east of a line from Shoreline to
Camano to Mt. Vernon. Fog/mist may also develop over the East Strait
of Juan de Fuca, over Whidbey Island into western
Whatcom/Skagit/Snohomish Counties (as well as the Cascades, and
between Olympia/Centralia). These will all lift Friday morning and
clear out by the afternoon. Winds this afternoon are variably out of
the W/SW and W/NW at 4 to 8 kt (higher winds gusting to 20 kt will
be possible later this evening coastline/Strait of Juan de Fuca
areas). Most areas will see light and variable winds overnight,
becoming W/NW during the day Friday.

KSEA...VFR skies continuing this afternoon (with cumulus clouds
scattering out in and around the terminal). Winds have become west
at 4 to 8 kt this afternoon. Diffluence from the Strait of Juan de
Fuca may bring northwesterlies briefly this afternoon, but the
direction is expected to remain W/SW through the afternoon below 6
kt, becoming light and variable overnight. MVFR stratus is expected
to return Friday morning (as early as 12-14Z), but will scatter out
late morning/afternoon. Winds Friday will become northwest 4 to 6 kt
by the afternoon.

HPR

&&

.MARINE...A trough over B.C. Canada will continue to move inland
today. Ridging will continue to remain offshore through this
weekend, as onshore flow continues with northwesterly winds over the
coastal waters. Gusty winds to 25 kt are expected over the outer
coastal waters late today into Friday, as well as central/east
Strait of Juan de Fuca late today. Small craft advisories will
continue in these areas. Seas will also build up to 8 to 9 feet at 8
to 10 seconds in the outer coastal waters with this stronger push
(due to the stronger winds). In addition, areas of patchy to dense
fog are possible over the east Strait of Juan de Fuca, Admiralty
Inlet, and Northern Inland Waters Friday morning. The fog may bring
visibilities down to a quarter of a mile in some areas.

The remainder of this weekend into next week will see calmer winds
out of the west or southwest as the ridge moves inland. A couple of
weak frontal systems will move through the area next week, but are
not expected to produce gusty winds. Seas will drop to 4 to 6 feet
over the weekend, increasing to 5 to 7 feet next week.

HPR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT Friday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 11 PM this evening to 5 PM PDT Friday
     for Coastal Waters From Cape Flattery To James Island 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

&&

$$