Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 131211
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
411 AM PST Thu Dec 13 2018

.SYNOPSIS...Wind and mountain snow will taper off today as a front
moves through the area. Another strong system will move through
the area Friday with high winds possible along the coast. After a
little break on Saturday the active weather pattern will resume
with additional weather systems reaching the area Sunday through
the middle of next week.

&&

.SHORT TERM...Satellite imagery shows cloudy skies over Western
Washington this morning with most observation sites reporting rain
at 3 am/11z. Winds have eased a little since midnight with the
strongest winds over the Northwest Interior, San Juan Islands and
along the coast. Temperatures at 3 am were in the 40s.

Current front moving through the area later today. Winds will
continue to slowly ease this morning. Have confined the wind
advisory to the Northwest Interior until noon. Rain rates will
ease as well later this morning into the afternoon hours with the
rain coming to an end late in the day over the Southwest Interior.
Snow levels rising as Western Washington moves into the warm
sector. This combined with a reduction in precipitation rates will
bring about an end to the winter storm warning for the mountains
at noon. Highs will be in the upper 40s and lower 50s.

A little break in the action tonight as the warm front lifts
north into British Columbia in response to the trailing cold
front becoming more north south oriented offshore. Surface
gradients becoming more easterly with the winds continuing to ease
overnight into early Friday morning. Have gone ahead and dried out
the Southwest Interior tonight with just chance pops for the
Central Puget Sound. Front not lifting far enough north to keep
the northern portion of the area out of the rain. Western
Washington remaining in the warm sector with snow levels rising as
high as 6000 feet tonight. It will remain mild overnight from
about Seattle northward with plenty of cloud cover keeping
temperatures in the mid 40s. A little clearing over the southern
portion of the area will allow temperatures top drop as low as
the upper 30s.

Models having trouble coming up with a consistent solution for
where the surface low associated with the next system will track
on Friday. The 00z ECMWF and GFS track the 980-985 mb low into the
northern end of Vancouver Island late Friday afternoon with the
KAST-KUIL gradient peaking around plus 10 mb in the afternoon as
the bent back occlusion reaches the coast. The 00z NAM was a
little stronger with the gradient. The 06z GFS has a much further
south solution to the surface low with the low moving inland near
the West Entrance to the Strait of Juan de Fuca. Even the weaker
00z GFS and ECMWF solutions have 45-60 knot winds at 925 mb along
the coast Friday afternoon. With a majority of the solutions
pointing toward possible high winds along the coast will issue a
high wind watch for the coast for Friday morning and afternoon.
Best chances for high winds ( sustained winds as high as 45 mph
with higher gusts ) will be in 18z Friday to 02z Saturday ( 10 am
to 6 pm Friday ). Windy conditions developing over the Northwest
Interior as well on Friday. Rain will move into the area in the
morning and continue through the afternoon hours. Highs will be
mild, in the lower to mid 50s.

Front moving through the area early Friday evening with conditions
easing overnight as weak surface high pressure builds into the
area. A break in the weather on Saturday as the next system
eastward movement slows down in response to the parent low moving
north into the Gulf of Alaska.

.LONG TERM...Extended models in good agreement with a series of
fronts moving through the area Sunday through Wednesday of next
week. Each one of these systems has the potential to create windy
conditions especially along the coast and over the Northwest
Interior but at this point this Friday`s system looks to be the
stronger than any of the systems next week. Rain amounts in the
mountains and lowlands could be significant, increasing the risk
of landslides. None of the systems look particularly cold, but
snow levels should be low enough for periods of heavy snow in the
mountains. Felton

&&

.AVIATION...An upper level low passing well north of the area will
train in moisture keeping rain/showers over W WA for much of the
next 24 hours. Flow aloft will remain generally from the west.
Surface winds will remain breezy with occasional gusts as pressure
gradients remain tight for much of the TAF period. As such...will
leave wind shear present in TAFs that already include it. The
atmosphere will remain moist and generally stable.

Cigs over W WA this morning a mixed bag with VFR to MVFR conditions
over most locations...although IFR conditions are present along the
coast and over PWT. As rain persists over the area...could see
conditions degrade slightly...with sites reporting VFR occasionally
dropping into MVFR and sites reporting MVFR occasionally dipping
into IFR. Otherwise...not much variation...improvement or
degradation...expected in cigs over the next 24 hours. SMR

KSEA...Breezy conditions with occasional gusts resulting in
potential wind shear...periods of rain and little to no change in
cigs expected over the TAF period. Rain to taper into showers by mid-
morning although coverage is expected to remain widespread through
late this afternoon/early this evening. Cigs expected to remain
generally low-end VFR although may dip briefly into MVFR in showers.
Southerly winds around 15 kts with gusts ranging from 22-25 kts
still likely throughout the morning and into the afternoon before
starting to relax some by tonight to 9-13 kts.  SMR

&&

.MARINE....Next system continues to impact the area this morning
with gale force winds across all water with the exception of small
craft conditions in the central Strait. A brief lull in the strong
winds will take place late this morning through mid afternoon but it
will be brief. Next, stronger system quickly moves in in its wake
this evening - Friday where winds will likely pick right back up and
perhaps be stronger as gradients increase. For simplicity`s sake,
have extended current gale warnings through Friday afternoon for
coastal waters, west and east entrances to the Strait, northern
inland waters and Admiralty Inlet. Small craft advisory winds likely
in Puget Sound today -early Friday before gale force winds return
Friday afternoon. Small craft advisory for Rough Bar at Grays Harbor
will remain in effect into Friday. In addition, seas of 20 to 25
feet along the coast likely Friday. Have issued a high surf advisory
as dangerous beach conditions and localized beach erosion are
possible. Additional systems likely next week with small craft or
gale conditions from time-to-time. CEO

&&

.HYDROLOGY...Rain totals in the 2 to 4 inch range in the last 12
hours over the Southern and Western Slopes of the Olympics has
pushed the Skokomish river in Mason county is back up above flood
stage this morning. The river will remain above flood stage
through tomorrow cresting in the moderate flood category later
today. A flood watch remains in effect for the rest of the Olympic
Peninsula for the possibility of a variety of flooding with the
heavy rain. The Bogachiel River is rising rapidly this morning and
could reach flood stage later this morning. Other rivers flowing
of the Olympics will be monitored. Otherwise, additional flooding
is not expected through the end of the week.

A series of weather systems moving into the area next week
could result in more flooding for rivers flowing off of the
Olympics by the middle of next week. 00z model runs push the
atmospheric river scenario for the middle of next week north of
the area. Previous solutions have placed this feature over the
area which would expose more rivers to potential flooding in the
middle of next week. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until noon PST today for Cascades of Pierce
     and Lewis Counties-Cascades of Snohomish and King Counties-
     Cascades of Whatcom and Skagit Counties.

     Flood Watch through this afternoon for Admiralty Inlet Area-
     Central Coast-Eastern Strait of Juan de Fuca-Hood Canal
     Area-Lower Chehalis Valley Area-North Coast-Olympics-
     Western Strait of Juan De Fuca.

     Wind Advisory until noon PST today for San Juan County-Western
     Skagit County-Western Whatcom County.

     High Surf Advisory from 10 AM to 10 PM PST Friday for Central
     Coast-North Coast.

     High Wind Watch from Friday morning through Friday afternoon for
     Central Coast-North Coast.

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

     Gale Warning until 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 7 AM PST this morning for Central
     U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Friday morning through Friday afternoon for
     Puget Sound and Hood Canal.

     Small Craft Advisory from 10 AM this morning to 7 AM PST Friday
     for Puget Sound and Hood Canal.

     Gale Warning until 10 AM PST this morning for Puget Sound and
     Hood Canal.

&&

$$

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