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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KSEW 041223 CCA
AFDSEW

Area Forecast Discussion...CORRECTED
National Weather Service Seattle WA
423 AM PST Thu Mar 4 2021

.SYNOPSIS...Slow moving frontal system offshore will approach the
coast tonight and move through Friday afternoon. Upper level
trough moving across the area Friday night and Saturday morning.
Next system arriving Sunday. Upper level low offshore Monday
moving south into Wednesday pulling systems south of the area for
the first half of next week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Satellite imagery shows
frontal system well offshore with mid and high level clouds
spreading over Western Washington early this morning. Temperatures
at 3 am/11z were mostly in the 30s.

Frontal system offshore slowly moving east today with the leading
edge of the precipitation ahead of the front spreading over most
of the area in the afternoon. Increasing mid and high level
moisture this morning could result in some lenticular clouds
around Mount Rainier. Slow moving/stalling front offshore good
recipe for a warm day this time of year but with the thicker cloud
cover already near the coast and spreading inland this morning
will keep highs in the 50s.

Front stalling near the coast tonight with the large upper level
trough offshore between 130 and 140W digging south. Front close
enough to give the entire area precipitation overnight. Snow
levels rising to 4000 to 4500 feet tonight. Easterly cross
Cascade gradient not very strong, -4 or -5 mb, so do not expect
any cold air to get trapped in Stevens or Snoqualmie pass. Only
snow in the passes near the summit of White Pass. Breezy
conditions over the northern portion of the area with southerly
winds gusting as high as 40 mph. Lows Friday morning in the mid
40s.

Rain continuing Friday with the cold front finally moving through
Western Washington later Friday afternoon. Winter weather advisory
for the Olympics beginning this morning will come to an end late
Friday morning. 6 to 15 inches of new snow possible at Hurricane
ridge by late Friday morning. In the Cascades, snow levels
remaining above the passes. Air mass destabilizing quickly behind
the front with thunderstorms possible along the coast late in the
day. Highs Friday around 50.

Upper level trough offshore Friday night with the trough axis
near the coast by early Saturday morning. Precipitation decreasing
rapidly behind the front with just scattered showers across the
area. Still a chance of thunderstorms along the coast in the
evening. Lows Saturday morning in the mid 30s to lower 40s.

Trough axis moving through Western Washington Saturday morning
keeping a chance of showers in the forecast especially in the
morning. Showers will become confined to the higher terrain in the
afternoon. Highs Saturday a little on the cool side, mid 40s to
lower 50s.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Extended models and
ensemble solutions in good agreement with another front moving
through Western Washington Sunday. Snow levels in the Cascades
will be down around 2000 feet for snow in all the passes. Good
agreement in the extended models continues into the first part of
next week with a large vertically stacked low moving south off
the west coast Monday through Wednesday. Ensemble solutions have a
few members, less than 20 percent, with light precipitation.
Model blend gives slight chance pops through the period. With some
good consistency in the models at this point going to go dry for
the most part Monday through Wednesday and keep the slight chance
of showers wording just over the southern portion of the area at
times. Highs will continue to be a little below normal, a couple
of degrees either side of 50. Felton

&&

.AVIATION...Southwesterly flow aloft with an upper level ridge to
the east and a frontal system moving close to the coast this morning
hours. Breezy conditions expected this afternoon. Breezy
southerly winds return to Puget Sound by Saturday before tapering
off into Saturday evening.

Increasing clouds today as the frontal system approaches the coast.
Patchy fog will also likely return this morning with visibility
1-3sm over the Southwest Interior and the Kitsap peninsula until
approximately 18z. Rain beginning across Puget Sound between
00-03Z.

KSEA...Southerly winds continuing through the day, generally between
5-10 knots. Increase in cloud coverage expected as the frontal
system nears the area. Rain likely beginning at the terminal between
approximately 02-04z this afternoon.

Kristell

&&

.MARINE...A vigorous cold front will arrive later today and
slowly move through the waters into Friday. Winds across area waters
will increase throughout the morning, with gales expected offshore.

Offshore swells will remain elevated, between 13-16 feet, into
Friday morning before decreasing Saturday. Another swell train will
arrive on Sunday.

A number of marine headlines are posted for area waters today and
into Friday evening, including offshore gale warnings, and Small
Craft Advisories for much of in the inland waters. Additional marine
headlines may be posted Sunday into early next week as the unsettled
pattern continues.

Kristell

&&

.HYDROLOGY...Stalling front offshore will keep precipitation going
in the Olympics this afternoon through Friday afternoon. Snow
levels rising to about 4000 feet. Rainfall amounts in the 24 hour
period along the south slopes of the Olympics in the 2 to 3 inch
range. It is possible that the Skokomish River near Potlatch
reaches flood stage Friday morning. Will upgrade the hydrologic
outlook to a flood watch for Mason county with the morning
forecast package. Any flooding that does occur is expected to be
minor. Felton

&&

.CLIMATE...On this day back in 1955 Seattle experienced its
coldest March day on record. With 5 inches of snow on the ground
the low was 11 degrees, coldest temperature recorded in March in
Seattle. The high was also the coldest on record for March, 29
degrees. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 10 AM this morning to 10 AM PST
Friday for Olympics.

PZ...Gale Watch from late tonight through Friday evening 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 until noon PST today 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.

     Gale Warning from noon today to 10 PM PST this evening 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 until 4 PM PST Saturday for Grays Harbor
     Bar.

     Small Craft Advisory from 6 AM this morning to 7 PM PST Friday
     for Admiralty Inlet-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory from 6 AM this morning to 4 PM PST Friday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 4 AM to 10 AM PST Friday for Central
     U.S. Waters Strait Of Juan De Fuca.

&&

$$

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