Gale Warning 88, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
215 PM PST Sun Dec 16 2018

.SYNOPSIS...A weakening front will move through the area tonight
through early Monday bringing periods of light rain to the area.
After a brief break Monday afternoon, a strong front will move
slowly southeast across the area Monday night through Tuesday
bringing locally heavy rain and windy conditions with snow in the
mountains. Additional strong fronts will move through the area on
Thursday and late next weekend.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Satellite imagery and
observations show the incoming frontal system sitting from the
northern coast of Vancouver Island SSE to just off southern Oregon
coast. This front will drift slowly eastward across the area
tonight while it continues to weaken. Snow levels in the northern
Cascades have risen to about 5500 feet and precipitation rates
have decreased. Hence, the winter storm warning for the Cascades
of Whatcom and Skagit counties has been cancelled. Winds over the
northern interior zones have also diminished, so the wind advisory
there has been allowed to expire.

After a brief break Monday afternoon, the next in a series of
strong fronts will move through the area late Monday night through
Tuesday.

The flow to the south of this front has tapped into some
tropical moisture originating over the central Pacific west of
Hawaii and will produce heavy precipitation rates for several
hours before it finally moves through. Heavy rainfall rates will
likely continue into Tuesday morning for the interior south of
Tacoma, and total precipitation amounts of 3-5 inches are possible
over portions of the southern interior, the Cascades of Lewis and
Pierce counties, and the area near the Willapa Hills.

Strong flow aloft associated with this front will produce locally
windy conditions, likely into the wind advisory range of 30-35
mph with gusts to 50 mph, along the coast and in portions of the
north interior.

Snow levels 3500 to 4000 feet in the Cascades of Whatcom and
Skagit counties are low enough that heavy snowfall amounts can be
expected there with up to 2 ft accumulations before the front
comes through and precipitation rates decrease on Tuesday. A
winter storm watch is being issued for the Cascades of Whatcom and
Skagit counties Monday night and Tuesday.

Rain will become lighter and increasingly tied to the terrain
later Tuesday through Wednesday as onshore flow continues and
temperatures aloft cool somewhat.

Temperatures around the area through the short term will be
averaging 5-8 degrees above normal for mid December.

Albrecht

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...Models are in rather
good agreement and are reasonably consistent with their previous
solutions. They all show a deep low moving into northern Vancouver
Island on Thursday with its associated strong front moving across
Western Washington Thursday afternoon. This front promises to
bring another round of rain and wind.

Cooler air moves into the area for Thursday night through early
next weekend, and a somewhat dirty ridge aloft may produce some
light showers. Models show rather low snow levels between about
1000-2000 feet. Another strong and wet system will likely close
out next weekend. Albrecht

&&

.AVIATION...A weakening front will move inland this evening. A
weak upper trough will cross the area tonight. A strong frontal
system will reach the area late Monday. Southwest flow aloft
tonight will increase on Monday. The air mass is moist and stable
except unstable near the coast tonight.

Ceilings are generally VFR in rain across the area. MVFR ceilings
are expected to increase tonight behind the front as low level
flow switches from easterly to southerly. It's not forecast to be
especially soupy in the low levels tonight so ceilings below 3000
feet might be more hit and miss.

KSEA...Ceilings 5000-7000 feet are expected to lower to 2000-3000
feet tonight as a weakening front moves through and southerly
winds develop. Model cross sections and statistical guidance are
wishy-washy with the low clouds however. KTIW also developed some
VLIFR ceilings in the last hour out of nowhere so there is a
small chance some of that could affect the terminal tonight. In
general, confidence in the ceiling forecast for tonight is rather
low. Easterly wind wind 5-10 knots will become southerly this
evening. Schneider

&&

.MARINE...There will be a relative lull in between fronts tonight
and Monday morning. The next in a series of strong frontal
systems will bring another round of gales later Monday and Monday
night. Moderate to strong onshore flow will follow on Tuesday and
then ease on Wednesday. A third strong frontal system will bring
more gales Wednesday night and Thursday. Long period west swell
20-22 feet will affect the coast from late this afternoon through
Monday morning. A high surf advisory is in effect for the coast.
Schneider

&&

.HYDROLOGY...The Skokomish river rose back above flood stage
midday and a flood warning is in effect for that river. The next wet
frontal system will arrive late Monday afternoon and night, and then
it will start to sag south through the area Tuesday, probably ending
up over southwest Oregon Tuesday night. There will be a period of
pretty decent rainfall with 3-5 inches of rain below a snow level
around 5000 feet, and the front will be focused over southwest
Washington a bit longer than areas to the north. Then, Tuesday
evening the 850mb temp will drop to -1c over Western Washington,
turning the rain back to snow for the ski areas, and that relatively
cool dry gap will extend from Tuesday night into midday Wednesday. A
Hydrologic Outlook was issued that is a short summary of what is
mentioned in this discussion here to highlight the higher risk of
river flooding on some rivers.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...High Surf Advisory until 10 AM PST Monday for Central Coast-
     North Coast.

     Winter Storm Watch from Monday evening through Tuesday afternoon
     for Cascades of Whatcom and Skagit Counties.

PZ...Small Craft Advisory until 10 AM PST Monday 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 10 AM to 10 PM PST Monday 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 for rough bar until 4 PM PST Monday for
     Grays Harbor Bar.

     Small Craft Advisory until 9 PM PST this evening for East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 1 PM Monday to 1 AM PST Tuesday for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 1 PM PST Monday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory for hazardous seas until 10 AM PST Monday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Tuesday for Admiralty Inlet.

     Small Craft Advisory until 10 PM PST this evening for Puget
     Sound and Hood Canal.

&&

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