Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 151122
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
322 AM PST Mon Jan 15 2018

.SYNOPSIS...Today will be dry and mild for mid January. A
weakening frontal system will bring some rain and locally windy
weather tonight and Tuesday. A wetter frontal system will move
through Western Washington Wednesday and Wednesday night, followed
by cooler showery weather Thursday and Friday. Another frontal
system should keep the area cool and wet this weekend.

&&

.SHORT TERM...The upper ridge over the region is weakening as it
moves east of Washington early this morning, and southerly flow
aloft is increasing over Western Washington ahead of a deep upper
low near 46N/140W. A band of high clouds is lifting north across
the region, and there is some patchy fog. Temperatures at 2 am
were in the upper 30s and 40s.

The band of high clouds will lift north of the area this morning,
and the leading edge of the next frontal cloud band should arrive
later this afternoon; satellite imagery shows a rather clear slot
between the two. So we can expect high clouds over Western
Washington at times today, mainly to start and end the day.
Overall, partly sunny should be a good forecast for the area
today. Temperatures will be quite mild once again for mid January,
mainly in the lower to mid 50s across the lowlands; that`s around
8 degrees warmer than normal, and most spots will be within a
couple degrees of the record high for the day. Moderate easterly
gradients across the Cascades will produce locally windy
conditions, mainly in and near the Cascades.

A weakening, negatively-tilted occluded front will move across
Western Washington tonight, followed by its upper trough on
Tuesday. Precipitation amounts for tonight and Tuesday will be
modest at best: around 0.50 to 1.25 inches to the Olympics, mostly
a half inch or less elsewhere, and mostly less than a quarter
inch over the interior lowlands. The snow level will be 5000 to
6000 ft today and fall to 4000 to 4500 ft tonight.

Showers will decrease Tuesday night, as a minor upper ridge
progresses quickly across the area.

The next frontal system will bring rain and locally windy
conditions beginning Wednesday -- mainly in the afternoon -- and
Wednesday night. This system will be wetter, but still not enough
to produce flooding concerns. We can expect 1 to 2+ inches of
liquid equivalent precipitation in the mountains, with the snow
level rising to around 5500 ft as the front moves through. There
should be around an inch of rain at the coast and 0.25 to 0.75 in
the interior lowlands. McDonnal

.LONG TERM...An upper trough following the Wednesday/Wednesday
night front will keep Western Washington in a cooler showery
regime Thursday through Friday. Highs will be back in the mid to
upper 40s, which is close to normal. The snow level will be around
3000 ft on Thursday and 2000 ft on Friday, and two-day snow totals
of roughly 6 to 15 inches are a good bet in the mountains. The
models agree than at another Pacific frontal system will move
through the area over the weekend; it should be associated with a
fairly cool air mass, but weakening as it moves inland. McDonnal

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.AVIATION...Moderate southerly flow aloft as a front approaches the
coast today and moves inland tonight. At the surface, moderate
southeasterly gradients will develop as the front approaches. There
is patchy IFR fog, especially around south Puget Sound, but high
clouds have limited fog formation. What fog there is will linger
into the late morning, then dissipate. Clouds will increase and
ceilings will eventually become MVFR around the time rain begins.
Rain will develop on the coast around 00Z and spread inland 03Z-09Z.

KSEA...The threat of fog appears to be receding somewhat, as fog
around Tacoma has dissipated. High clouds will gradually thicken and
lower today. MVFR ceilings are likely in rain late tonight. Easterly
wind 4-8 kt today will become more southeast 8-12 kt tonight. CHB

&&

.MARINE...A front will approach the coast today and move inland
tonight. Winds will become southeasterly and increase. Gale force
winds are likely on the coast tonight, and these will probably
spread inland late tonight, to the east entrance and northern inland
waters. Gale warnings are now in effect.

Another system on Wednesday also seems likely to bring gales.
Westerly swells of 20 to 25 ft are possible Thursday. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 10 AM PST this morning for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

     Gale Warning from 10 AM this morning to 4 AM PST Tuesday for
     Coastal Waters From Cape Flattery To James Island 10 To 60
     Nm-Coastal Waters From James Island To Point Grenville 10
     To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

     Small Craft Advisory for rough bar until 10 AM PST Tuesday for
     Grays Harbor Bar.

     Small Craft Advisory until 4 PM PST this afternoon for Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Gale Warning from 4 PM this afternoon to 4 AM PST Tuesday for
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     Out 10 Nm.

     Small Craft Advisory from 7 AM this morning to 10 PM PST this
     evening for East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

     Gale Warning from 10 PM this evening to 10 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 4 AM PST Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

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