Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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574
FXUS66 KSEW 192326
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
326 PM PST Thu Jan 19 2017

.SYNOPSIS...A broad upper level trough will remain over the
offshore waters through the weekend. A series of systems rotating
around it will bring showers and breezy conditions at times to
Western Washington along with seasonable temperatures. By early
next week, a ridge of high pressure will build into the Pacific
Northwest for the possibility of several dry days.

&&

.SHORT TERM...A broad upper trough containing a closed low just
off the Washington Coast will continue to spin and produce showers
over Western Washington through Saturday night. A period of
lesser shower activity is possible Friday into Friday night and I
have adjusted the POPs accordingly. Friday morning, there is a
good chance of gusty conditions over the Cascade passes and
foothills as a tight pressure gradient sets up over the Cascades,
with higher pressures in Eastern Washington and lower pressures
inland.

On Sunday...a new and slightly more intense closed low will form
in the broad upper trough and its associated frontal system will
move through the area. As the jet stream is well to the south of
us and the low is stacked nearly vertical, the frontal system will
only be moderately vigorous. There is a good chance of rain over
portions of Western Washington on Sunday, tapering off to showers
Sunday night. JSmith

.LONG TERM...Monday through much of next week, models are in
agreement that an upper ridge will form over the area for a
change to a drier weather pattern. Temperatures are also likely to
cool by a few degrees. JSmith

&&

.AVIATION...An upper level low off the coast will turn flow aloft
over Washington southerly tonight and Friday. The air mass is moist
and slightly unstable with showers. Surface easterly gradients will
increase tonight as a low pressure center approaches the coast.
Ceilings are mostly MVFR 2-3K ft and will remain around this level
into the evening. Showers are forecast to diminish after midnight
and ceilings could improve to VFR then.

KSEA...Discussion above applies. Surface winds will remain southerly
8-14 KT this evening, then become more easterly after 09Z or so. CHB

&&

.MARINE...A deep low will form off the coast tonight and remain
there through Sunday. Fronts will spin around the low and reach the
area at a rate of about one per day Friday through Sunday. Small
craft advisory winds are likely with each impulse, and gale force
winds are possible in some places. For the first impulse on Friday,
a gale warning is in effect for the coast with small craft advisories
all other waters. The pressure gradient has a strong easterly
component, so a gale at the west entrance is not out of the question.

More fronts will arrive Saturday and again Sunday with small craft
advisory strength winds likely with each one. The Sunday system
looks a bit stronger and gales are possible then on the coast, at the
entrances, and over the northern inland waters. On Monday, the
deep low off the coast is forecast to move southeast into Oregon.
Offshore flow will develop Monday as high pressure builds over the
region. Winds will be light Tuesday.

A large westerly swell approaching 18-20 FT is forecast to reach the
coast on Saturday. CHB

&&

.HYDROLOGY...A flood warning remains out for the Skokomish River in
Mason county. Showers into tonight will slow the fall of the water
level on the Skokomish River. No additional river flooding is
expected for the remainder of the forecast period. An extended
period of dry weather appears likely to develop early next week.
JSmith

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 4 AM PST Friday 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 4 AM to 4 PM PST Friday 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 Friday for
     Grays Harbor Bar.

     Small Craft Advisory until 4 PM PST Friday 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-Puget Sound and Hood Canal-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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