Wind Advisory 15, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
912 PM PST Mon Nov 25 2019

.SYNOPSIS...Upper level low pressures settles over the region
through the week with much colder air mass arriving. Some showers
through Tuesday evening, but otherwise dry conditions are
expected the rest of the week. A strong low pressure system tracks
well south of the area on Wednesday, bringing increasing winds to
the region, especially across the northern portions of the
forecast area. The next disturbance will move closer to the area
late in the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...Radar as of 8PM this
evening shows conditions generally drying across the area, with
precipitation activity, and isolated thunderstorms with small hail,
over portions of the central Puget Sound area and extending to
southern Snohomish and northern King Counties. Aside from the PSCZ
activity, a few spotty showers will be around through tonight
though generally drier weather is expected as flow towards
offshore. Much cooler air will filter into Western Washington as
this offshore flow develops tonight into Tuesday. Precipitation
activity is expected to generally be in the form of rain tonight
with snow levels around 1,000 feet, however, a rain/snow mix in
spots is possible if a steadier PSCZ forms. The main area of focus
may very will be with the current PSCZ over portions of southern
Snohomish County as it shifts with offshore flow developing. No
snow accumulations are expected.

A strong surface low will develop offshore on Tuesday and track
into the OR/CA Tuesday evening into Tuesday night. Although fairly
well out of the area, the surface low may extend wrap-around
moisture into southern portions of the area, generally Lewis
County, where there is a chance for light rain or a rain/snow mix
Tuesday morning into the afternoon. No accumulations are expected.
Strong outflow through the Fraser River Valley will also develop
late Tuesday through Wednesday with the surface low positioned
over southern Oregon. Wind gusts expected to be 50-55 MPH on
Wednesday for the San Juans, and western Whatcom and Skagit
County. A High Wind Watch is in effect for this area. Breezy
conditions otherwise expected across the area with strong offshore
winds. Temperatures will also be cold Tuesday night and Wednesday
night with lows in the low 30s for Tuesday night and 20s for
Wednesday night. Dry and cold conditions for Thursday. High
temperatures on Thursday will be in the upper 30s to low 40s. JD

.LONG TERM /FRIDAY THROUGH MONDAY/...Dry and cold conditions
continue Friday and into the weekend. Overnight low temperatures
will likely drop into the mid 20s near the urban centers, but into
the lower 20s in the suburbs and more rural locations. Daytime
highs will only top out in the upper 30s or perhaps as warm as 40
in a few area. This will likely hold through Saturday and perhaps
through early Sunday, until the next disturbance approaches the
forecast area. Specifically, a developing low pressure system is
modeled to track from the southwest into the Oregon or southern
Washington coast. The leading round of moisture with this
disturbance will likely spread into the region sometime Sunday or
Monday. The air mass will be quite cold ahead of its arrival
through, and will need to keep an eye on the precipitation type
(rain vs snow) as this moves into the region. Still plenty of
spread among guidance though, so for now just something to keep an
eye on. Cullen

&&

.AVIATION...Northwest flow aloft tonight with southwesterly flow
aloft by Tuesday afternoon. Onshore flow at the surface tonight
will transition offshore on Tuesday. The air mass is somewhat
moist and unstable. VFR cigs early tonight with mid level clouds.
MVFR cigs expected for most sites by late tonight into the
morning. It will be marginally cold enough for any showers to mix
with snow late tonight, but aside from PSCZ activity, drier
weather is expected. Winds will be southerly tonight and
transition northerly by Tuesday afternoon.

KSEA...VFR cigs to transition to MVFR late tonight through Tuesday
morning. Southerly winds tonight and become northerly by the
afternoon and strengthen. JD

&&

.MARINE...Onshore flow tonight will transition offshore on Tuesday
as a low tracks southeast through the Oregon coastal waters.
Offshore flow will strengthen Tuesday night and Wednesday with
gale forecast northeast winds possible for the Northern Inland
Waters and the Strait of Juan de Fuca. Offshore flow will weaken a
bit Thursday and Friday and increase on Saturday.

11-13 foot west swell over the Coastal Waters will subside below
10 feet on Tuesday. JD

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...High Wind Watch from Tuesday evening through Thursday morning
     for San Juan County-Western Skagit County-Western Whatcom
     County.

PZ...Small Craft Advisory until 4 AM PST Tuesday 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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory for rough bar until 4 AM PST Tuesday for
     Grays Harbor Bar.

     Gale Watch from Tuesday evening through Thursday morning for
     Northern Inland Waters Including The San Juan Islands.

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

&&

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