Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 260436
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
836 PM PST Thu Feb 25 2021

.UPDATE...The forecast remains on track this evening with no
changes planned. Water vapor imagery this evening depicts broad
cyclonic flow extending from the far NE Pacific and into the
Western US, while at the surface, high pressure continues to nose
into the Pacific Northwest off the Pacific, with this morning`s
cold front now located across Eastern WA and through Northern
California.

Scattered showers continue across the area this evening amidst a
marginally unstable environment. Despite favorable placement of
the left exit region of a 300mb jet streak and cold mid level
temperatures, the lack of surface heating and meager lapse rates
prevented the development of thunderstorms today, and the threat
will remain minimal through the overnight hours. For tonight, can
expect shower coverage to taper some through about midnight as mid
level heights attempt to rise between shortwave troughs. After
midnight, shower coverage is expected to increase as a shortwave
rapidly dives south through the area from Haida Gwaii and central
BC Coast vicinity. These showers will likely continue until
daybreak where the shortwave will then continue its journey south
of the area. Will still see some shower activity across the area
on Friday as favorable jet dynamics and an unstable environment
continue. There is some evidence of some convergence zone type
features developing again Friday afternoon, which may bring some
heavy snow to the mountains through Saturday morning.

A high wind warning will remain in effect through 10AM Friday for
the Admiralty Inlet area as strong west winds continue down the
Strait of Juan de Fuca (See NPWSEW). Swells will also increase
offshore to between 20-25 feet overnight and into Friday morning,
bringing high surf conditions to the Coast. Previous discussion
follows with an updated aviation section.

Kovacik

&&

.PREV DISCUSSION... /issued 235 PM PST Thu Feb 25 2021/

.SYNOPSIS...A cool showery air mass will remain over Western
Washington through Friday. Strong onshore flow and westerly winds
aloft will give the mountains periods of heavy snow. A break in the
weather will come Saturday followed by weaker weather systems and a
chance of rain at times into next week.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Strong onshore flow will
persist tonight and Friday. The air is somewhat unstable and there
are PSCZ showers from the north part of Hood Canal east through
southern Snohomish and northern King county. It hasn`t been all that
convective however, radar shows tops around 16kft at 2pm, so the
chance for a tstm is probably negligible. A winter storm warning is
up for the Cascades and orographically enhanced periods of heavy
snow will make for wintry pass conditions with blowing snow and
poor visibility at times. Snowfall rates today were not really
all that impressive, but there is a good chance that it will pick up
tonight into Friday morning and h850 winds should get up around
50kts. Gale westerlies are blowing in the Strait of Juan de Fuca and
a high wind warning is up for Whidbey Island/Admiralty Inlet area.

The showers will decrease later Friday and Friday night and for the
lowlands there should be more sunbreaks Friday afternoon. Saturday
should be a decent day, dry, light winds, and some sunshine. As we
get into Saturday night and Sunday the chance for rain will increase
again ahead of the next weather system. 19

.LONG TERM /MONDAY THROUGH THURSDAY/...A front will probably move
through Western Washington Monday morning, and then another
system will reach the area Tuesday and Wednesday while a bit of a
ridge tries to build. The models are not in agreement at all (GFS
mostly dry, Euro and Canadian mostly wet) so all that can be done
for now in the extended forecast is too keep a chance of rain
through the period, waiting for the models to converge. 19

&&

.AVIATION...Northwest flow aloft with upper level disturbance
moving across the region overnight. The air mass is moist and
somewhat unstable. Strong low level onshore flow will
continue through Friday. VFR ceilings expected with the exception
of shower activity in the convergence zone. A secondary
disturbance will swing through the region overnight for more
widespread MVFR ceilings with showers. Gusty surface winds in
excess of 30 knots at times will continue this evening,
especially near the coast and for areas in the vicinity of the
Strait of Juan de Fuca.

KSEA...MVFR cigs. The majority of convergence zone activity
should remain north and east of the terminal through this evening.
However, a secondary convergence zone is expected to develop
overnight and slide southward early Friday morning reaching the
terminal 09Z- 11Z. Surface winds SW 10-20 knots. Winds could
shift W-NW near or after 12Z.

&&

.MARINE...Strong post frontal onshore flow continuing into Friday.
Gale warnings are up for a majority of the waters. Winds ease
late Friday into Friday night. Weak high pressure will build over
the waters on Saturday for lighter winds. A weakening front will
brush the area on Sunday. Coastal swell increase tonight in the 20
to 22 foot range. Seas in the low 20 foot range will continue
until late Friday afternoon before gradually subsiding over the
weekend. 27

&&

.HYDROLOGY...Flooding is not expected over the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 10 PM PST Friday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties.

     High Surf Advisory until 4 PM PST Friday for Central Coast-North
     Coast.

     High Wind Warning until 10 AM PST Friday for Admiralty Inlet
     Area.

     Winter Weather Advisory until 10 AM PST Friday for Olympics.

PZ...Small Craft Advisory until 4 PM PST Friday for Grays Harbor Bar-
     Puget Sound and Hood Canal.

     Gale Warning until 10 AM PST Friday for Admiralty Inlet-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 4 PM PST Friday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De
     Fuca.

     Gale Warning until 10 PM PST this evening for Northern Inland
     Waters Including The San Juan Islands.

&&

$$

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