Gale Warning 74, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
742 PM PST Thu Dec 17 2020

.UPDATE /THIS EVENING/...An area of showers, associated with a
convergence zone across southern Snohomish/northern King counties,
continues this evening. This will slowly drop south and dissipate
over the next few hours. A brief break in the action is expected
before the next system moves onshore overnight into Friday
morning. Showers associated with this system are just beginning to
appear on the coastal radar. Have updated precipitation forecast
to account for latest trends, otherwise forecast remains intact.
Previous discussion follows with updates to the aviation and
marine sections. Carpenter

&&

.SYNOPSIS...The next front will arrive Friday afternoon for
another round of blustery wet weather. A rather wet frontal
system will reach Western Washington over the weekend. The
snow level will rise through Saturday night with heavy rain
in the mountains. A cold front will move through the region
on Monday. Drier weather is possible for a few days next week.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...The next front will arrive
Friday afternoon and evening. This looks like a pretty run of the
mill front but should muster southeast gales for the windier spots
like the coastal waters and around the San Juans and Whidbey Island.
It does not look remarkable otherwise--but it will set the stage for
another system that will be warmer, stronger, and wetter for the
weekend. Saturday night and Sunday morning will see the snow level
rise with a period of heavy rain in the mountains. 3-6 inches of
rain looks like what we will see in the mountains--perhaps a bit
less in the north, possibly focused more in the central and south
Cascades. The lowlands ought to pick up an inch or two (except less
in the typically rain-shadowed areas). How long the front lingers
before sagging down toward the Oregon-WA border is tricky, but there
has been a trend to shift the heavy rain from Vancouver Island and
the Olympics plus the north Cascades down to southwest Washington and
the southern Cascades for the past two model runs. 19

.LONG TERM /MONDAY THROUGH THURSDAY/...A cold front and cold upper
trough will arrive Monday. The Monday weather system has a range of
interesting possibilities, but for now the forecast is a blend of
the solutions and doesn't reflect the 12z wrfgfs idea for heavy
precip behind a cold front dragging down the snow level. After that,
there is a good chance that a period of drier weather will develop
for two or three days next week. 19

&&

.AVIATION...After some brief scattering late this afternoon, MVFR
ceilings are beginning to redevelop this evening at most terminals.
This should remain the dominant category through much of this TAF
cycle. Some light shower activity is expected to graze mainly the
northernmost terminals Friday morning with coverage then quickly
increasing in both coverage and intensity from the west during the
afternoon and evening hours. Winds S overnight 10kts or less,
increasing Friday afternoon and becoming gusty at times, sustained
10-15kts (potentially 20-25kts at HQM) and gusts 20-25kts (30-35kts
HQM).

KSEA...MVFR the dominant ceiling category through this TAF cycle. A
few light showers possible Friday morning, with more substantial
coverage by mid-late afternoon. Winds S 10kts or less overnight,
increasing 10-15kts Friday afternoon with gusts near 25kts. Winds
will slowly ease and rain will taper to showers Friday night.

Kovacik

&&

.MARINE...Winds will continue to ease this evening as earlier
frontal system departs. The next system will arrive Friday with
another bout of strong winds and high seas. Gale warnings or small
craft advisories are in place for all waters through Friday
evening. A small craft advisory also remains in effect for Grays
Harbor Bar due to severe bar conditions. Another system will
arrive for the weekend and will likely prompt additional
headlines.

Carpenter

&&

.HYDROLOGY...The Skokomish river in Mason county fell below flood
stage at Potlatch this afternoon, so the flood warning was ended
there. A front will move in Friday afternoon for some wet blustery
weather, but it is the front coming in Saturday night that is the
one that could cause problems for more than just the Skok. As
noted above, 3-6 inches of rain looks like a good forecast for the
mountains, but there has been a trend to shift the heavy rain
from the north down to southwest Washington and the southern
Cascades for the past two model runs. 19

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 7 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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Gale Warning from 7 AM to 4 PM PST Friday for Admiralty Inlet-
     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-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 4 PM PST Friday for Grays Harbor Bar.

     Small Craft Advisory until 10 PM PST this evening 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.

     Small Craft Advisory from 7 AM to 4 PM PST Friday for Central
     U.S. Waters Strait Of Juan De Fuca-Puget Sound and Hood
     Canal.

&&

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