Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 102312

Area Forecast Discussion
National Weather Service Seattle WA
312 PM PST Mon Dec 10 2018

.SYNOPSIS...A series of vigorous fronts will move through the
area over the next week. The first one will arrive on Tuesday with
locally windy conditions and heavy mountain snow. There will be a
lull on Wednesday followed by the next system Wednesday night and
Thursday. This system will hang up over the area before pushing
inland later Friday. Another system will arrive on Sunday.


.SHORT TERM...A vigorous frontal system will bring rain, wind,
and mountain snow later tonight and Tuesday. Wind advisories are
up for the usual southeast sucker locations - coast and Northwest
Interior. Isolated high wind is not out of the question for the
San Juan Islands and Western Whatcom county for a few hours Tuesday
morning. The Cascades will get heavy snow Tuesday and Tuesday
night. Snow levels will start out 2500-3000 feet but models show
snow levels rising to 4000-4500 feet Tuesday afternoon and
evening which means snow will probably turn to rain at Snoqualmie
Pass and perhaps even at Stevens Pass. About a foot of new snow is
expected at Snoqualmie Pass with up to two feet at Stevens Pass
and 2-3 feet at Mount Baker and Paradise. The winter storm watch
has been upgraded to a warning.

There will be a brief lull in between fronts on Wednesday with
the next frontal system fast approaching. This aforementioned
second frontal system will bring another round of rain, wind, and
mountain snow to the area Wednesday night and Thursday. Schneider

.LONG TERM...A frontal system will push inland on Friday with
rain, wind, and mountain snow tapering. It could get rather windy
on Friday as a deep surface low tracks onshore but models are
having a tough time agreeing on the track and strength of the low
so how windy it will get is very uncertain for now. There will be
a break in between fronts on Saturday then another front on
Sunday. This front is splitting as it moves onshore and looks like
a garden variety December system. Yet another frontal system will
be moving into the area later Monday. This system could
potentially be the wettest of the week. Schneider


.AVIATION...An upper trough is moving inland, northwest flow aloft
will become southwest and increase Tuesday with the next frontal
system. There are still clouds and some showers over the mountains,
but areas of clearing over the lowlands this afternoon. Mid and high
level moisture associated with the next frontal system will begin to
spread into the area this evening. As the next frontal system
arrives MVFR ceilings and rain will develop along the coast tonight
and spread inland around daybreak. Gusty SSE surface winds will
develop--especially coastal areas and the north interior of Western
Washington, then turn more southwesterly later in the day with the
frontal passage.

KSEA...Today saw a break between fronts but rain will develop again
with lowering cigs overnight. On Tuesday winds at 5000 feet will be
SW near 50 knots and blustery southerly surface winds will pick up--
especially in the afternoon as the front passes and winds shift from
SE to SSW.


.MARINE...Today saw a lull in the active weather before the next
front arrives Tuesday. Gale warnings are in effect for all waters
except the central Strait of Juan de Fuca and Puget Sound--where the
wind should stay in the small craft advisory category. After a break
later Tuesday night and Wednesday morning another vigorous front
will arrive Wednesday night. That front looks like it will stall
over Western Washington on Thursday and then another frontal wave
will arrive with an increase in pressure gradients again on Friday.
The details are still being sorted out, but that system could be the
strongest this week, but it is highly uncertain right now and the
model guidance differs a great deal.


.HYDROLOGY...A series of storms will cross over the region during
this next week, bringing periods of rain roughly every other day.
This will drive the rivers back up again with the cumulative effect
pushing the Skokomish River in Mason county likely over flood stage
Tuesday night and maybe over moderate flood stage late this week -
and possibly other rivers by that time as well. There is a flood
watch out for Mason County and the Skokomish River for Tuesday
night. The best chance for flooding in general will probably be
Friday when a frontal system could hang up over the area. One major
factor working against flooding on many rivers will be the
moderately low snow levels (4000 to 5000 ft dropping to 3000 ft
Friday) which might limit storm runoff. jbb


WA...Winter Storm Warning from 4 AM Tuesday to 4 AM PST Wednesday for
     Cascades of Pierce and Lewis Counties-Cascades of Snohomish
     and King Counties-Cascades of Whatcom and Skagit Counties.

     Flood Watch from Tuesday morning through Tuesday evening for
     Hood Canal Area-Lower Chehalis Valley Area-Olympics.

     Wind Advisory from midnight tonight to 1 PM PST Tuesday for
     Admiralty Inlet Area-San Juan County-Western Skagit County-
     Western Whatcom County.

     Wind Advisory from midnight tonight to 10 AM PST Tuesday for
     Central Coast-North Coast.

PZ...Small Craft Advisory for rough bar until 2 AM PST Wednesday for
     Grays Harbor Bar.

     Gale Warning until 1 PM PST Tuesday 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 from 1 AM Tuesday to 2 AM PST Wednesday for
     Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 1 AM to 10 PM PST Tuesday for Puget
     Sound and Hood Canal.


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