River Flood Warning 48, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
427 PM PST Wed Feb 5 2020

.SYNOPSIS...A warm front stalled over the area through Thursday. A
frontal system will move through Thursday afternoon into Friday
night. A system will slide across Western Washington Friday
afternoon into Friday night with an upper level trough moving
across the Pacific Northwest on Saturday. Dry northerly flow aloft
Sunday into Monday with an upper level ridge offshore. A system
will move through on Tuesday.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...Radar imagery this
afternoon shows steady stratiform rain King County northward with
a rain shadow over portions of the South Sound with northwesterly
flow aloft. A warm front is stalled across the Olympic Peninsula
with temperatures in the mid to upper 40s this afternoon.

Fairly consistent weather pattern through Thursday night with the
stalled warm front and Pacific moisture aimed at Western
Washington. Highest QPF amounts in the Lowlands will be along the
coast as well as Snohomish and Skagit Counties. Rain shadow
generally south of King County with light amounts for the central
Puget Sound and South Sound. Rain amounts upwards of 3-5" are
possible through Thursday night for the Cascades, especially the
central and southern Cascades. Rivers will rise rapidly into
Thursday (refer to the Hydro Discussion). Gradient in snow levels
across W WA through Thursday with levels 6000-7000 feet south of
Snoqualmie Pass and 4000-5000 feet north of I-90. Rain at
Snoqualmie Pass through Thursday night with a rain/snow mix at
Stevens Pass at times, although Stevens Pass is a bit trickier
with snow levels hovering around Pass level there.

The frontal system will move east Thursday night into Friday for
possibly a brief dry period Friday morning (though limited) as the
next system slides southeastward along Vancouver Island Friday
into Friday night. Snow levels will lower rapidly as the front
moves through, with snow levels around 2000-2500 feet by Saturday
morning for light-moderate snow amounts in the Cascades. Gradients
will rise with the system (PDX-BLI around 12mb) with general
consensus taking the track just north of the area. Breezy to windy
conditions possible Friday night into Saturday because of this,
especially along the coast. The magnitude of the winds will need
to be monitored. Conditions will dry out by Saturday evening as an
upper level ridge builds offshore. Temperatures into Saturday in
the upper 40s to low 50s.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Upper level ridging will
build over the area into Sunday with dry weather (and some
sunshine) through Monday. Ensembles are consistent with a system
riding along the periphery of the ridge and moving south over
Western Washington Monday night into Tuesday for a round of
precipitation. Upper level ridging is expected to build back in
for Wednesday for drier weather. Cooler weather pattern for at
least early to middle next week with highs in the mid 40s. JD

&&

.AVIATION...Moist, westerly flow will continue across western WA
today for rain across the region. The air mass is stable. LIFR to
IFR ceilings are likely to continue through this afternoon. Slight
vsby and ceiling improvement to MVFR category possible this evening
before the next round of rain enters the region.

KSEA...Expect rain and LIFR visibilities through this afternoon,
with possible MVFR conditions into the evening and overnight hours.
Winds generally south to southwesterly through the period between 8-
15kts.
Kristell

&&

.MARINE...Strong onshore flow will prevail over the waters
through Thursday - Small Craft Advisories remain in effect.
Another strong Pacific frontal system will arrive Friday night and
Saturday with gales possible and seas building to 15 to 25 feet. The
flow will ease Saturday night then turn offshore on Sunday.
Additional marine headlines will likely be needed by Friday
into Saturday.
Kristell

&&

.HYDROLOGY...precipitation totals for the last 24 hours ranged from
1 to over 5 inches in the mountains and up to one and a half inches
in the lowlands. the heavy rainfall will continue over the area
through mid-day Friday for another 5 to 7 inches in the central and
southern Cascades and 2 to 4 inches in the northern Cascades and
Olympics. One to two inches more can be expected in the lowlands
outside of the rain shadowed area south of Seattle to Olympia to the
east slopes of the Olympics due to the west northwest flow aloft.
The next heaviest period of rainfall looks to be Thursday afternoon.
Snow levels range from 4000 to 6000 feet in the Cascades, north to
south, and 6500 to 7500 feet in the Olympics. This amount of
precipitation could produce flooding on many rivers, streams, and
urban areas. Some flooding has already begun on the White River and
other Flood Warnings are out as well. The current orientation of the
flow aloft puts the heaviest precipitation over the central and
southern Cascades. Rivers in those area with dams on them, that
don't flood very often, are all at risk of flooding, such as the
Cedar, Green, White, Nisqually, and Cowlitz Rivers. A flood watch
also remains in effect ( see product FFASEW for the latest). In
addition, the landslide threat is also be elevated for the period
during this event and a few days after. River forecasts are being
updated as new information comes in so check for the latest. Bower

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through Friday afternoon 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-San Juan County-Seattle
     and Vicinity-Southwest Interior-Tacoma Area-Western Skagit
     County-Western Strait of Juan De Fuca-Western Whatcom
     County.

     Winter Weather Advisory until 6 PM PST this evening 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 PM PST Thursday 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-Grays Harbor Bar-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Thursday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 10 PM PST this evening for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 4 PM PST this afternoon for Puget
     Sound and Hood Canal.

&&

www.weather.gov/seattle

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
512 PM PST WED FEB 5 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0510 PM     HEAVY RAIN       2 S COUPEVILLE          48.19N 122.68W
02/05/2020  M2.25 INCH       Island             WA   TRAINED SPOTTER

            RAINFALL FROM MIDNIGHT TO 5 PM. STILL RAINING

&&

GRUB