Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 222333

Area Forecast Discussion
National Weather Service Seattle WA
333 PM PST Fri Feb 22 2019

.SYNOPSIS...Onshore flow will continue tonight for showers and
mountain snow. A cool upper trough will follow the front this
weekend. A system may bring more lowland snow to the region late
Sunday night and Monday.


.SHORT TERM /TONIGHT THROUGH MONDAY/...We had mixed precipitation
as a cold front moved in today, but most areas are now reporting
rain with temps in the 40s. Showers will mainly impact the
Cascades tonight with scattered coverage elsewhere. We`ll likely
see a band of heavier showers in King county due to a Puget Sound
Convergence Zone. A Winter Weather Advisory remains in effect for
the west slopes of the Cascades where 6-11" of snow is expected
through tonight.

Snow levels will remain low through the weekend with a cool upper
level trough over the region. We may see rain/snow mix with the
showers but significant accumulations are not expected. Daytime
max temps will be in the 40s which should limit impacts from any
lowland snow. Showers will taper down on Sunday.

There is another threat of lowland snow late Sunday night and
Monday, but there`s still a lot of uncertainty in the details. We
have a classic setup (overrunning event) where snow levels will
remain low (near the surface) while moisture spreads north from a
warm front. What`s unknown is how far north the moisture will
reach and how long the duration will be. The latest ECMWF is
wetter compared to the GFS for a wide range of snow totals.
Nonetheless, we may see more winter weather impacts in the CWA and
will continue to monitor how this system evolves. 33

.LONG TERM /TUESDAY THROUGH FRIDAY/...Showers will continue
through the rest of the week as an upper level trough stalls
offshore then shifts inland. Guidance shows we will remain a few
degrees below normal through the period. Snow levels will be
higher, mostly in the 1,000-2,000 ft range, for rain in the
lowlands. We may see a break in the action toward the end of the
week as a ridge builds in. 33


.AVIATION...Northwesterly flow aloft will persist briefly in the
wake of a cold front, before shifting back to the west during the
overnight hours. Ceilings have already improved for terminals
along the coast and are expected to improve for Puget Sound
terminals around 00-04Z as the band of heavier precipitation
continues to move southeastward out of the area. Ceilings could
become VFR behind the frontal passage, however are expected to
become MVFR again overnight as a moist post- frontal air mass
remains in place and surface gradients weaken.

KSEA...Current radar imagery has indicated that rain has tapered
off at the terminal over the last hour. Current IFR ceilings are
expected to lift in the wake of the frontal passage, with MVFR
ceilings remaining possible as the airmass remains moist. Surface
winds have shifted to the southwest and will continue to ease
into the overnight hours. 14


.MARINE...Small craft northwesterlies will persist along the
coastal waters in the wake of a cold frontal passage. Winds have
shifted to the west in the Strait and increased to near gale-
speeds for areas along the central and eastern Strait. A weak
surface low will move south to the Oregon coast by Sunday morning.
Northeasterly offshore flow will redevelop late Saturday night
and continue through Tuesday with high pressure over British
Columbia and lower pressure to the south of Washington. 14


.HYDROLOGY...River flooding is not expected for the next 7 days.


WA...Winter Weather Advisory until 6 AM PST Saturday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory until 4 AM PST Saturday 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.

     Small Craft Advisory for rough bar until 9 AM PST Saturday for
     Grays Harbor Bar.

     Gale Warning until midnight PST tonight for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 6 PM PST this evening for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until midnight PST tonight for Admiralty
     Inlet-Puget Sound and Hood Canal-West Entrance U.S. Waters
     Strait Of Juan De Fuca.


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