Small Craft Advisory 265, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT Wed Nov 1 2017

.SYNOPSIS...A cold front will move through the area today. An upper
level low will drop down over the region on Thursday. Northeasterly
Fraser winds will develop by about Thursday evening for windy
weather for the Bellingham area out through the San Juans. This first
weather system will move inland Friday and Friday night and another
weather system will arrive Saturday night and Sunday morning.

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.SHORT TERM...Precip today will mainly be in convergence zones and
in the mountains. The snow level this morning looks to be around
4500 feet in the central Cascades. Cooler air will drop over the
region as an upper trough develops and moves south. The snow level
will fall Thursday kick in around thursday evening. Dry air will
filter into the area through Friday and the showers will diminish.
The lowlands will flirt with snow showers but the precip might very
well dry up before it is cool enough to snow. Maybe some upslope
around Port Angeles will help the foothills around there get
some snow Thursday night or Friday morning--it will be chilly,
but not especially cold--getting the snow level down to the
surface will depend on wet bulb cooling. Friday afternoon through
Saturday morning look dry as the trough moves inland and northerly
flow aloft and dry low level northeast flow with easing Fraser
outflow continues.

.LONG TERM...A second upper trough digs down over the area Saturday
night and Sunday morning. The 06z GFS shows some nice development of
precip and surface low pressure development that tracks toward
Astoria by daybreak Sunday. That system will need the wet bulb
effect and heavier precip to get some snow falling--probably a
good chance of snow on the hills of Southwest WA. It will be
interesting to see how low the dewpoints get Friday and Saturday and
how the models change as far as where the heavier precip goes. It is
awfully early in the year to get excited about lowlands snow but the
pattern is pretty good around daybreak Sunday for Southwest WA.
After that system moves through conditions should be cool and dry
gain by about Sunday afternoon through Monday before a third system
arrives around Tuesday. That system is likely to be warmer and more
typical.

&&

.AVIATION...An upper trough over B.C. will pinch off into a closed
low and sink southward down Vancouver Island through Thursday.
Strong northwest flow aloft today will become strong westerly on
Thursday. Cooling temperatures aloft will lead to an increasingly
unstable air mass, with low-level moisture becoming deeper. Spotty
showers today will become more widespread on Thursday. Ceilings in
the 020-040 range will be most common through Thursday.

KSEA...Cigs will predominantly rise into the 025-035 range this
afternoon and evening. Could be a few convergence zone showers
from 21z-02z (2 pm-7 pm) at the terminal, which could briefly
bring cigs lower. Light and variable winds are expected during
that same time as the convergence zone makes it closest approach
to SEA, but a full-on turn to north wind is not expected. South
wind will resume this evening. Haner

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.MARINE...Needed to extend the Gale Warning for the Central and
Eastern Strait based on observed conditions at 7 am. UIL-BLI
gradient is in the process relaxing, and winds are showing signs
of easing. So the updated expiration time of noon might be
generous.

Hoisted SCA for Puget Sound through early afternoon mainly for
gusty southwest winds south of the Narrows.

In the bigger picture, onshore flow will ease this afternoon. A
1004 mb low pressure center will develop near the coast of Central
Vancouver Island on Thursday and sink southward through the
Coastal Waters on Thursday night. Meanwhile, strong surface high
pressure will develop over the interior of B.C. tonight and
Thursday, initiating a Fraser Outflow wind episode on Thursday,
continuing on Friday. Thursday's timing of the onset of Fraser
Outflow winds is quite a bit sooner than was being advertised
yesterday. Northeast gales appear likely on Thursday and Friday
for Fraser-Outflow prone waters, especially north of the San Juan
Islands. Haner

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Thursday 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 from 8 AM this morning to 5
     PM PDT this afternoon for Grays Harbor Bar.

     Small Craft Advisory until 5 PM PDT 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.

     Small Craft Advisory until 11 AM PDT this morning for Admiralty
     Inlet-Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

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www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html