High Wind Watch 3, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
945 AM PST Sun Nov 25 2018

.UPDATE...The precipitation forecast has been updated to reflect the
latest short range guidance. Showers are advancing toward the WA
coast late this morning and are likely to reach the western portions
of the Puget Sound before sunset. Rain will overspread western WA
this evening and overnight. The latest BUFR soundings for Stampede
Pass continue to indicate the potential for freezing rain tonight
through Monday morning. After collaborating with NWS Spokane, we
will issue a Winter Weather Advisory for freezing rain above 2500
feet from 7pm this evening through noon Monday. Main concern is
freezing rain over the mountain passes. Ice accumulations are
currently expected to remain under a quarter inch.
-Wolcott-

&&

.SYNOPSIS...High pressure aloft will prevail today. A weakening
warm front will bring light precipitation to mainly the Olympic
range westward during the day today. Rain will increase tonight as
another, but stronger, warm front approaches from the west. This
front will sweep across the area on Monday, resulting in locally
heavy rain and gusty winds. A cold front will move across the area
late Monday night or early Tuesday. Expect scattered showers on
Tuesday behind the front.

&&

.SHORT TERM...
There was virga (precipitation not reaching the surface) or a few
sprinkles over the far northwest interior at this time. Doppler
radar imagery showed a larger, but discontinuous, area of rain
just offshore moving east. This area of rain is associated with a
weak warm front that will move across the WA coastal waters during
the day. The best chance of precipitation will be over the
western part of the CWA but amounts will be light.

Meanwhile, high pressure aloft will prevail over the region today
for dry weather for much of the area. The threat of rain will
slowly increase tonight as a stronger warm front approaches from
the west and moisture transport strengthens. Rain rates should
begin rapidly increasing over the south-southwest slopes of the
Olympic range late tonight.

On Monday, periods of heavy rain can be expected on the north
coast and south-southwest facing slopes of the Olympic range.
Locally heavy rain is expected on the southwest slopes of the
north Cascades Monday afternoon. It appeared that the heaviest
rain will occur Monday night, where local amounts of up to 10
and 7.5 inches on the Olympic range and north Cascades,
respectively, could fall during the 24-hour period ending at 4 AM
PST, Tuesday. In general, the models were a little wetter than
the previous runs. This means that there will probably be more
rivers, draining off the Olympics and north Cascades, approaching
flood stage. A Flood Watch was issued for the Skokomish River in
Mason County. This river is forecast to reach flood stage Monday
evening.

Expect the cold front to move across the area on Tuesday for
falling snow levels. Rain rates will also quickly drop off behind
the front but there will be a few more rivers, such as the
Nooksack, in flood or close to flood stage during this time.

Another concern will be wind. The models, in general, were
stronger with wind speeds for the Monday afternoon through Monday
night time frame. It looks like wind speeds will probably reach
advisory criterion over parts of the coast and northwest interior.
A Wind Advisory will probably need to be issued with the afternoon
forecast package. The current forecast indicates that the
strongest winds will occur during the day Monday but the latest
guidance shows that it will be Monday night. Gusts could also
reach 50-55 mph in a few places such as Whidbey Island.

.LONG TERM...
It looks like a weak split flow regime will prevail during this
period, with the southern jet being the most active. Overall,
anticipate a cool and showery weather pattern during this period.
At this time, do not see any major storms impacting the area.

&&

.AVIATION...Upper level ridging over the area will shift eastward
through Monday. A strong frontal system well offshore will push
slowly eastward through the coastal waters late tonight through
Monday. With exception to local IFR conditions in typically fog-
prone areas in the south interior through 20Z, the air mass is
stable and dry with increasing moisture at mid and high levels.
Most terminals will remain VFR into late tonight or Monday morning
as increasing SE to E flow in the boundary layer holds ceilings up.
Conditions in valleys in the south interior and areas on the east
and north slopes of the Olympics will likely see conditions
deteriorate to IFR to MVFR late tonight into Monday morning.

Note that areas of LLWS will develop after 10Z as southerly flow
aloft between 2000 and 3000 ft increases to south 45 to 55 kt.
Albrecht

KSEA...High clouds today will thicken and lower this evening and
rain will develop overnight. Light SE winds. Conditions are expected
to remain VFR through Monday morning. LLWS is expected to develop
around 2000 ft AGL late tonight into Monday as boundary layer flow
remains rather light out of the SE and at 2000 ft S wind increase to
around 45 kt. Albrecht

&&

.MARINE...A weak front is dissipating over the coastal waters
today. A strong frontal system offshore will move slowly east
through the coastal waters later Monday and through the inland
waters Monday evening. Gale conditions are expected to develop over
the coastal waters this evening and rapidly spread to from extreme
northern portions of Admiralty Inlet to the Northern Inland Waters,
including the eastern entrance to the strait. Small craft advisory
conditions are expected through the western 2/3 of the strait and in
Puget Sound and Hood Canal.

The large expanse of gales ahead of the incoming front will allow
combined seas over the coastal waters to build to between 16 and 21
feet late Monday through Monday evening.

Winds and seas will gradually subside starting Tuesday as weather
systems move well to the south of the area. Albrecht

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 7 PM this evening to noon PST
     Monday for Cascades of Pierce and Lewis Counties-Cascades
     of Snohomish and King Counties-Cascades of Whatcom and
     Skagit Counties.

     Flood Watch from Monday afternoon through late Monday night for
     Hood Canal Area-Lower Chehalis Valley Area-Olympics.

PZ...Small Craft Advisory for rough bar from 4 AM Monday to 6 AM PST
     Tuesday for Grays Harbor Bar.

     Small Craft Advisory until 5 PM PST this afternoon 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 5 PM this afternoon to midnight PST Monday
     night 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 6 PM this evening to midnight PST Monday night
     for Admiralty Inlet-East Entrance U.S. Waters Strait Of
     Juan De Fuca-Northern Inland Waters Including The San Juan
     Islands.

     Small Craft Advisory until 6 PM PST this evening for East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 11 PM PST Monday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

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