Heavy Snow in Washington, February 4, 2019

Area Forecast Discussion
National Weather Service Seattle WA
815 PM PST Sun Feb 3 2019

.SYNOPSIS...Cold air will continue to spill out of British Columbia
through Monday while an upper level low moves south offshore. This
combination will bring snow showers to most of the area through
Monday morning. Dry but cool weather is expected Tuesday and
Wednesday. Another round of cold and unsettled weather is expected
Thursday through next weekend.

&&

.UPDATE...Radar and spotter reports show snow showers continuing
north of Seattle, while another blob moves onto the central coast.
There are weak echoes elsewhere, for instance in Seattle proper, but
these are probably flurries. Made a short term update to the grids
for QPF and snow amount. Some 00Z mesoscale model runs were
available for the update, and they show another band of snow showers
affecting most zones 06Z-12Z. This seems likely to drop another inch
or two of snow, so have expanded the winter weather advisory area to
cover all zones from Everett south, including Seattle. Streets in
the urban core will probably not get much accumulation, but grassy
areas and streets in outlying areas will accumulate 1-3 inches
overnight into Monday morning. Don't look for a lot of melting right
away as skies will be cloudy and a cold north wind will keep
temperatures around 30 in the morning, with highs on Monday in the
mid 30s.

Snow will end, from north to south, during the day Monday. Upslope
winds will keep the snow going along the strait, especially on the
northern slopes of the Olympics. Those zones could flirt with
warning amounts. On Monday night skies will clear from north to
south, and the snow threat will be over for a few days at least.

Strong northeast winds have finally arrived in the north interior.
These are forecast to continue through Monday night, and a high wind
warning remains in effect. Burke

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Just a little busy here
at NWS Seattle this afternoon.

Doppler radar shows broad area of convergence from King county
into Whatcom county. Satellite imagery shows upper level low over
the northern tip of Vancouver Island with shower bands rotating
around the low off the coast. Doppler radar has the first of these
bands just offshore at 00z/4 pm. Temperatures at 4 pm were in the
30s.

Here is the current thinking on the snow forecast. Convergence
area, which did not form because of the cold air moving out of
British Columbia but because of the westerlies through the Strait
earlier today combined with southerly up the Puget Sound and the
cold air aloft, will diminish this evening with the flow through
the Strait going easterly. There still will be an area of
convergence as the cold air spills out of British Columbia but
this area will not cover near as much area as the current
convergence. Have a winter weather advisory for another inch of
snow in Snohomish, Skagit and Whatcom counties this evening with
the convergence. Next up the shower band currently offshore moving
inland over the southern portion of the area tonight.
Temperatures are currently just above freezing but dew points are
below freezing so once the precipitation begins temperatures will
fall and the precipitation type will change from rain to snow
this evening. Precipitation amounts to not look very heavy 0.20
inches or less overnight into early Monday morning. Have issued a
snow advisory for the central Coast, Lower Chehalis valley and
Southwest Interior for up to two inches of snow through early
Monday morning. Snow advisory also up for the Eastern Strait of
Juan de Fuca and the Admiralty Inlet area with some upslope flow
into the northern slopes of the Olympics enhancing the
precipitation rates later tonight into Monday morning.

So where does this leave the metro area??? Once the convergence
lifts north this evening there will be a little break in the
precipitation over the central Puget Sound area. Temperatures in
the metro area are currently in the lower to mid 30s.
Precipitation rates are light and the temperatures are marginal.
While there will be snow in the air for the evening hours with
the light precipitation rates only going to forecast up to an
inch overnight into early Monday morning.

Monday morning, most of the models are still developing a
deformation zone somewhere over the central and southern portion
of the interior Monday morning. As previously mentioned it is hard
to pin down the exact location and intensity of this feature with
much lead time. A couple of model trends are a little worrisome
about the development of this feature, one the upper level low
southward movement is slower than the models have predicted which
means two the cold air is still somewhat bottled up to the north.
Less low level convergence will result in lower precipitation
amounts if the deformation zone forms. For this forecast package
will have a possible addition up to an inch of snow accumulation
over the central interior including the Puget Sound region in the
4 am to 10 am window. Outside of the deformation zone showers
will still be rotating around the low with the best chances for
accumulating snow over the southern portion of the area. With
another inch or so of accumulation possible the snow advisory for
the Southwest Interior will continue until 1 pm. Upslope flow into
the northern slopes of the Olympics will also continue through
the morning hours will another 1 to 2 inches of snow possible
along the Eastern Strait of Juan de Fuca keeping the winter
weather advisory going there until 1 pm as well.

Monday afternoon, upper level low moving slowly south offshore
pulling the moisture with it south of the area. With the low
moving a little slower than the model forecasts have extended the
chance for snow showers from about Skagit county southward into
the early afternoon hours. By late afternoon the snow shower
chances will be confined to the southeast portion of the area.
Highs on Monday will be cool, only in the 30s with some places
near the Canadian border remaining in the 20s.

Drying trend Monday night as the low continues to move south with
a sunny but cool day expected on Tuesday. With the clearing skies
the cooler locations will fall into the teens Monday night. Highs
on Tuesday will be in the 30s and lower 40s.

Here is the current thinking on the wind. High wind warning still
in effect for San Juan as well as Western Whatcom and Skagit
counties beginning this evening and continuing into Monday night.
Cold air a little behind schedule but the winds at Ferndale are up
to 20 mph gusting to 40 mph at 4 pm. Winds will continue to
increase over the Northwest interior overnight as the Bellingham
to Williams Lake gradient becoming more negative as the much
colder air over British Columbia cools even more overnight ( the
temperature at Williams Lake at 4 pm was 11 below zero ). The
forecast of northeast winds 25 to 45 mph with gusts as high as 55
mph through Monday night remains intact.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Little change in the
extended forecast this afternoon. Models continuing with the idea
of another cool upper level low moving down close to the area
toward the end of the week with another round of low snow levels.
Timing of the feature still inconsistent among the models so will
continue with the broad brush idea of chance pops through the
period with below normal temperatures. Felton

&&

.AVIATION...An upper low southwest of Vancouver Island will move
south over the offshore waters tonight and into the Oregon waters on
Monday. Southwesterly flow aloft will become southeasterly Monday
morning. At low levels, strong northeast to north flow will
gradually spread south across the region through early Monday as low
pressure passes by to the west and southwest, and high pressure
remains over the interior of British Columbia. The air mass will be
moist and somewhat stable through Monday morning. Low MVFR and areas
of IFR ceilings in snow showers are expected through Monday. VFR
ceilings could develop across the far north portion of the area
early Monday as dry, colder air filters into the region. Ceilings
will improve to VFR over the Puget Sound area Monday afternoon.

KSEA...MVFR with periods of IFR persisting tonight into Monday AM.
Snow showers developing...with accumulations of 1-2 inches at the
terminal most likely occurring between 05Z and 15Z. Some improvement
in ceilings expected Monday afternoon as drier air filters into the
area. Surface winds shifting to northerly 01Z-03Z and rising to 10
to 15 gusting 20 to 25 knots toward 12Z Monday.  27

&&

.MARINE...Flow will turn strongly offshore late today as a surface
low moves south over the offshore waters and a surface ridge
strengthens over the interior of British Columbia. Fraser outflow
will continue through Monday night. Gale force wind over the
northern inland waters this evening will spread to the Strait of
Juan de Fuca and adjacent coastal waters late tonight. Small craft
advisory strength winds will occur across the remainder of the
inland waters. Winds will ease on Tuesday as the outflow weakens.  27

.HYDROLOGY...River flooding not expected in the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 7 AM PST Monday for Bellevue and
     Vicinity-Bremerton and Vicinity-East Puget Sound Lowlands-
     Everett and Vicinity-Hood Canal Area-Seattle and Vicinity-
     Tacoma Area.

     Winter Weather Advisory until 1 PM PST Monday for Admiralty
     Inlet Area-Eastern Strait of Juan de Fuca-Lower Chehalis
     Valley Area-Southwest Interior-Western Strait of Juan De
     Fuca.

     High Wind Warning until 4 AM PST Tuesday for San Juan County-
     Western Skagit County-Western Whatcom County.

     Winter Weather Advisory until 10 PM PST this evening for Western
     Skagit County-Western Whatcom County.

     Winter Weather Advisory until 6 AM PST Monday for Central Coast.

PZ...Small Craft Advisory until 4 PM PST Monday for Admiralty Inlet-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     Out 10 Nm.

     Gale Warning until 4 PM PST Monday 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 Point
     Grenville To Cape Shoalwater 10 To 60 Nm-East Entrance U.S.
     Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Gale Warning until 4 AM PST Tuesday for Northern Inland Waters
     Including The San Juan Islands.

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

&&

www.weather.gov/seattle

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
1246 AM PST MON FEB 4 2019

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

1235 AM     SNOW             LAKE STEVENS            48.02N 122.06W
02/04/2019  M4.0 INCH        SNOHOMISH          WA   TRAINED SPOTTER

1235 AM     SNOW             MARYSVILLE              48.06N 122.15W
02/04/2019  M3.9 INCH        SNOHOMISH          WA   PUBLIC

1230 AM     SNOW             NORTH BEND              47.50N 121.79W
02/04/2019  M5.0 INCH        KING               WA   PUBLIC

1200 AM     SNOW             SNOHOMISH               47.91N 122.10W
02/04/2019  M3.5 INCH        SNOHOMISH          WA   PUBLIC

1150 PM     SNOW             1 N MONROE              47.87N 121.97W
02/03/2019  M3.0 INCH        SNOHOMISH          WA   PUBLIC

&&

CEO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
1254 AM PST MON FEB 4 2019

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

1245 AM     SNOW             DUVALL                  47.73N 121.97W
02/04/2019  M4.0 INCH        KING               WA   PUBLIC

1240 AM     SNOW             1 WNW MALTBY            47.81N 122.13W
02/04/2019  M2.5 INCH        SNOHOMISH          WA   TRAINED SPOTTER

1200 AM     SNOW             1 WSW SUMMIT            47.17N 122.38W
02/04/2019  M2.1 INCH        PIERCE             WA   TRAINED SPOTTER

            SINCE 615PM. WATER EQUIV 0.16 IN.

1145 PM     SNOW             2 S GRANITE FALLS       48.06N 121.97W
02/03/2019  M3.5 INCH        SNOHOMISH          WA   PUBLIC

&&

CEO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SEATTLE WA
152 AM PST MON FEB 4 2019

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

0130 AM     SNOW             MILL CREEK              47.86N 122.21W
02/04/2019  M5.5 INCH        SNOHOMISH          WA   PUBLIC

&&