785
FXUS66 KSEW 150414
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
815 PM PST Thu Nov 14 2024

.SYNOPSIS...Showers will continue to taper off tonight across
western Washington before an upper ridge brings a brief break in the
weather Friday. Cool and unsettled conditions return this weekend
and will persist into early next week as another wet system moves
into the area. Upper level ridging developing along the West Coast
may bring drier conditions and warming temperatures towards the end
of next week.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Latest radar imagery
continues to show downward trend in precip over W WA this evening.
The majority of the action remains over the eastern Sound, slowly
plodding toward the Cascades but weakening on its trek. That said,
there are two patches of precip producing estimated rainfall rates
of 0.5 to 0.7 inches per hour...one over southwestern Snohomish
county and the other just starting to exit Seattle and its immediate
metro area...so the prospect for brief periods of moderate to heavy
rain are still out there. Outside of that, looking west there are
some isolated showers over portions of the Olympic
Peninsula...however matching radar to satellite, some of the present
echoes /those that are not moving/ likely to be ground clutter and
not precip.

The threat of coastal flooding persists along the coast, but as
inundation levels around the Sound continue to fall, the threat has
ended there...thus allowing that portion of the advisory to expire.
The coast remains under this headline into late Friday morning.

Otherwise, inherited forecast remains on track with no need for any
additional updates. For additional forecast details, please refer to
the Previous Discussion section below.

From Previous Discussion...Shower activity will gradually taper off
tonight as an upper level trough axis slowly pivots eastward. Friday
will provide a brief break to wet conditions as high pressure builds
overhead. With a saturated surface layer, patchy fog is likely to
develop near the Puget Sound early Friday morning. Cloudy skies will
persist across western Washington through the afternoon Friday with
a few sun breaks possible outside of isolated light shower activity.

Coastal flooding concerns continue on Friday, particularly along
the Pacific Coast where tidal forecasts show potential for minor
coastal flooding Friday morning and early afternoon. This may lead
to the flooding of shorelines and low-lying coastal areas. The
threat for coastal flooding along the Pacific Coast will continue
through the weekend with astronomical high tide levels approaching
minor flooding thresholds, and the potential for the inner coast
looks to be lower but continues to be monitored.

Another wet storm system will move into the region on Saturday,
bringing in more widespread precipitation and breezy winds. Snow
levels will rise above 5000-6000 ft throughout the day Saturday as
a warm front lifts across the region and brings in ample moisture.
Precipitation may start as snow over the Cascade Passes on
Saturday before quickly changing over to rain as snow levels
rapidly rise. A cold front will cross western Washington on
Sunday, maintaining precipitation and bringing snow levels back
down to as low as 2000 ft by Sunday evening. Snow over the
Cascades will pick up as the cold front passes the region, with
heavy snow at times and potential for significant snow
accumulation through the Cascade Passes, particularly Stevens Pass
northward.

.LONG TERM /MONDAY THROUGH THURSDAY/...From Previous
Discussion...Periods of moderate to heavy precipitation will
continue on Monday as another cold front crosses the region. Snow
levels may dip as low as 1500 ft, with showers and breezy winds
favored to continue into Tuesday.

Ensemble and deterministic forecast guidance continue to show good
agreement over warming and drying by next Wednesday, with
potential for a strong upper level ridge to build over the western
US. While uncertainty remains in its strength, this would
primarily shift the storm track to the north of the area and would
promote drier and warmer conditions for western Washington
heading into the second half of the week.

15

&&

.AVIATION...Southwest flow aloft tonight will become weak and
variable as an upper low moves into the area by early Friday
morning. North to northwesterly flow aloft expected at times in the
mid to late morning before going straight north by Friday afternoon.
Northerly surface winds 5-10 kts in place over PAE, SEA and BFI this
evening thanks to some convergence zone activity with southwest to
westerly winds elsewhere. Light and variable winds along the coast.

A mix of VFR to MVFR conditions currently in place over W WA with
MVFR conditions largely where rain is or has recently been /south
and east Sound/. With lingering low level moisture from continued
active weather earlier in the day, expectation is for most terminals
to dip down into MVFR conditions overnight with those more prone to
lower cigs /such as OLM/ to drop down into IFR by early Friday
morning. Area-wide improvement to VFR conditions expected by late
morning/early afternoon for all terminals.

KSEA...Conditions recovering to VFR at the time of this writing now
that band of light to moderate precip has pushed east of the
terminal...although continued PSCZ activity keeping winds from the
north at 10-15 kts. Winds expected to ease and shift southerly by
around 06Z and remain there for the remainder of the TAF period with
speeds generally 4-8 kts. Cigs overnight will lower due to
aforementioned low level moisture with MVFR conditions emerging
around 09Z before recovering back to VFR after 18Z Friday.

18

&&

.MARINE...Onshore flow behind an eastbound surface trough this
evening. Ridging will build across the area late tonight into Friday
as conditions relax and remaining headlines expire. A front looks to
enter on Saturday with another round of headlines expected to go
with it. Here we could see widespread SCA winds along with possible
gales over the coastal waters. A secondary system coming onshore on
Sunday will keep advisory level winds going at least for the coastal
waters. Surface ridging is expected to rebuild over the waters on
Monday then shift inland for a period of offshore flow. Then, a
stout low could bring strong winds to area waters on Tuesday.
Coastal seas are expected to finally dip below 10 feet later Friday,
but will build back into double digits Sunday through Monday night.

McMillian/18

&&

.HYDROLOGY...From Previous Discussion...Showers will gradually taper
in coverage tonight into tomorrow. Rivers are cresting and will
begin to fall tonight into tomorrow. The Skokomish River has begun
to recede and could fall below flood stage tomorrow into Saturday.

Another system will move into the region this weekend into early
Monday, bringing another round of more widespread precipitation to
the area. Snow levels will fluctuate quite rapidly, with snow levels
rising up to 5000-7000 ft Saturday then back down to 2000-4000 ft on
Sunday. Expect rises on area rivers, with the largest rises expected
on the north and central Cascade rivers. Currently no river flooding
is forecast outside of the Skokomish river, which may return to
minor flood stage by Sunday. Flooding potential will depend on
temperatures, QPF, and snow levels and will continue to be monitored
over the next few days.

62

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Coastal Flood Advisory from 8 AM to 2 PM PST Friday for Central
     Coast-North Coast.

     Winter Storm Watch from late Friday night through Monday evening
     for West Slopes North Cascades and Passes-West Slopes North
     Central Cascades and Passes-West Slopes South Central
     Cascades and Passes.

PZ...Small Craft Advisory until 4 AM PST Friday for Grays Harbor Bar-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 11 AM PST Friday 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.

&&

$$