River Flood Warning 35, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
1001 PM PST Fri Jan 31 2020

.SYNOPSIS...Wet and windy conditions continue across the region
through Saturday with a strong cold front sliding south across
Western Washington

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.SHORT TERM /TODAY THROUGH SUNDAY/...Wind and rain, as expected,
remain the big story this evening with strong winds across much of
Western Washington. Gusts of 59 mph at Paine Field in Everett and
in Arlington were both noted, with several other locations
reporting gusts above 50 mph. Meanwhile, the band of heavier rain
remains across the northern Olympic Peninsula and extending
northwest across Island and Whatcom counties. A few minor
adjustments to the forecast this evening to reflect the current
position of the front and associated heavier rainfall beginning to
move slowly south a bit faster than the forecast previously
indicated. The remainder of the previous short term discussion
remains valid and follows below. Cullen

Rain ahead of the next cold front will start to push into W WA
overnight tonight with the front moving in throughout the morning.
Not only does this bring another round of precip...but will also
drag snow levels down to between 1000-2000 ft by Saturday evening.
Fortunately...the timing of when best precip will occur does not
line up with when the lower snow levels move into the area. This
should keep snow amounts in the mountains below any headline
criteria. On the topic of the white stuff...matching precip
chances with the presence of the colder temps Sat night into
Sunday morning continues to pose forecast problems. Current
solutions do not show these factors lining up all that well
and...as such...there might be some mixed precip or possibly some
light flurries...but accumulating lowland snow does not really
seem to be all that likely at this time.

Sunday sees a weak front move into the area and models do not really
hold this feature together very well. In addition...daytime heating
nudges snow levels up back into the 1000-2000 ft range and thus
should keep the precip generally liquid for the majority of lowland
locations. 18

.LONG TERM /MONDAY THROUGH THURSDAY/...Both long term deterministic
models suggest dry conditions for Monday as an upper level ridge
sets up over the Pac NW but cold air does not seem to be going
anywhere in a hurry once it sets in as highs for Monday and Tuesday
still sit in the lower 40s for the interior lowlands. Next system
moves in by Tuesday afternoon models suggest the prospect of another
atmospheric river scenario. The positioning of an upper level ridge
over the Pacific looks to keep the fire hose aimed squarely at W WA
for the remainder of the forecast period. On the plus side...this
will allow for snow levels to climb...bringing a return of high
temps in the 50s for the lowlands starting Wed. The big question is
at the onset of this system...will things warm up enough to keep
lowland precip from being snow. Models at this time generally opting
for mixed precip for a fair number of locations...but certainly
cannot rule out things starting off with flakes. This will warrant
watching for future forecasts. 18

&&

.AVIATION...Strong southwesterly flow aloft across the region,
with a strong cold front approaching the region. A mix of IFR and
MVFR in rain will continue overnight with heaviest rain sliding
south by early Saturday. Meanwhile, gusty south surface winds
continue for much of the region tonight with gusts 35 to 55 kt.
Expect a switch to west winds through the strait Sat morning,
bringing a surge of gusty NW winds down to KPAE. Winds likely
remain south to southwest from KBFI and points south.

KSEA...Mix of MVFR/low VFR ceilings this evening and overnight
with strong southerly surface wind and gusts to 30-35 kt
continuing overnight. Winds become southwest Saturday afternoon
and will ease.                                 Cullen

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.MARINE...A strong cold front will cross the area early Saturday
with a deep low moving onshore over Haida Gwaii. Strong onshore flow
will develop behind the front on Saturday. Gale force winds expected
all waters tonight and a few isolated storm force winds remain
possible over the coastal waters and near the west entrance of the
Strait of Juan de Fuca. Gale force westerly winds will follow
behind the front on Saturday, with again a few isolated storm
force winds through the Strait around daybreak Saturday.

Winds will ease Saturday night. A weak trough will cross the area on
Sunday. Light offshore flow will develop on Monday. Another frontal
system will reach the area on Tuesday. 27/12

&&

.HYDROLOGY....The mild and wet weather pattern continues into
early Saturday as the plume of very moist air will drop south
across Western Washington. This plume has been positioned across
the northern Olympic Peninsula and northeast into the northern
Cascades and into southern British Columbia. With very heavy rain
observed around Mt Baker and in the North Cascades, several new
flood warnings were recently issued. Widespread minor to moderate
river flooding is most likely but major flooding cannot be ruled
out and river models are showing that. Though there is greater
uncertainty about major category flooding. Rivers from King County
northward are at greatest risk of reaching moderate to major
flood severity.

A flood watch remains in effect for the area except for San Juan
and Island counties. See FFASEW for the latest. The threat of
landslides will increase again starting this evening as the rain
returns and remain high through this weekend.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through Sunday morning for Admiralty Inlet Area-
     Bellevue and Vicinity-Bremerton and Vicinity-Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties-Central
     Coast-East Puget Sound Lowlands-Eastern Strait of Juan de
     Fuca-Everett and Vicinity-Hood Canal Area-Lower Chehalis
     Valley Area-North Coast-Olympics-Seattle and Vicinity-
     Southwest Interior-Tacoma Area-Western Skagit County-
     Western Strait of Juan De Fuca-Western Whatcom County.

     Wind Advisory until 7 AM PST Saturday for Bellevue and Vicinity-
     Bremerton and Vicinity-East Puget Sound Lowlands-Eastern
     Strait of Juan de Fuca-Seattle and Vicinity-Southwest
     Interior-Tacoma Area.

     High Wind Warning until 7 AM PST Saturday for Central Coast-Hood
     Canal Area-North Coast-San Juan County-Western Skagit
     County-Western Strait of Juan De Fuca-Western Whatcom
     County.

     High Wind Warning until 10 AM PST Saturday for Admiralty Inlet
     Area-Everett and Vicinity.

PZ...Small Craft Advisory until 4 AM PST Saturday for Grays Harbor
     Bar.

     Gale Warning until 4 PM PST Saturday for Central U.S. Waters
     Strait Of Juan De Fuca-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.

     Gale Warning until 6 PM PST Saturday for Admiralty Inlet-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 6 AM PST Saturday for Northern Inland Waters
     Including The San Juan Islands.

     Gale Warning until noon PST Saturday for West Entrance U.S.
     Waters Strait Of Juan De Fuca.

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

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