Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 251040
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
340 AM PDT Fri May 25 2018

.SYNOPSIS...A low pressure system offshore will move over the area
today before exiting Saturday morning. Weak high pressure aloft
will prevail this weekend for near or slightly above normal
temperatures. A low pressure system will approach the region on
Memorial Day; however, it should be dry for outdoor activities.

&&

.SHORT TERM...
A stratocumulus deck blanketed much of the interior at this time.
Overall, not anticipating clouds to be as extensive as yesterday
morning. Highs today will be about the same as yesterday.

Meanwhile, an upper level trof offshore will move over the CWA
this afternoon and will be east of the area Saturday morning. The
main impact this system will have on our weather will be to
tighten the low level onshore pressure gradient and deepen the
marine layer. Therefore, expect patchy drizzle late tonight thru
Saturday morning.

A flat upper level ridge or near zonal flow aloft will prevail
this weekend. The low level onshore pressure gradient will be
weaker on Sunday; therefore, temperatures on Sunday will be
several degrees warmer than on Saturday.

.LONG TERM...
Memorial Day is still expected to be dry, and temperatures should
be about the same or slightly lower than on Sunday. So, it still
looks like a nice day for outdoor activities.

The GFS and Canadian models were now close to the ECMWF solution
in regards to the timing of the midweek system. Thus, the ECMWF
was the model of preference for this period (Memorial Day thru
Thursday). Expect onshore flow to strengthen on Memorial Day in
response to the approaching upper level trof. This trof will move
the area on Tuesday for cooler and cloudier conditions. The models
were drier with this system; therefore, decided to confine the
mention of showers to the Puget Sound Convergence Zone and the
north Cascades.

The Pacific Northwest will remain under the influence of low
pressure aloft Wednesday through Thursday for below normal temps.
There will be a chance of showers over mainly the mountains and
within the Puget Sound Convergence zone.

&&

.AVIATION...An upper level ridge to the east of the area combined
with troughing offshore will give southwest flow aloft through
today. The trough will move east across the area tonight deepening
the marine layer over the area Saturday morning. At the surface,
high pressure offshore combined with lower pressure east of the
Cascades will give low level onshore flow today. The onshore flow
will increase tonight as the upper trough moves across the area.

Wide variety of ceilings over the area this morning. For the central
Puget Sound ceilings near 3000 feet. From about Whidbey Island
northward ceilings are around 7000 feet. Along the coast ceilings
are near 2000 feet. Little change in the ceilings this morning with
the cloud deck becoming scattered around midday across the entire
area. MVFR ceilings will develop again along the coast tonight with
the stratus spreading inland after midnight.

KSEA...Ceilings around 3000 feet scattering out midday. Ceilings in
the 1000-2000 foot range with possible visibilities 3-5sm in light
drizzle Saturday morning. Variable wind 5 knots or less becoming NW
5-10 knots in the afternoon. Felton

&&

.MARINE...A ridge of high pressure sitting along 130W with a
trough over Eastern Washington will give varying degrees of
onshore flow for the next several days.

The onshore flow was strong Thursday night and will relax
somewhat early this morning. Onshore flow will again become
strong this afternoon and tonight as a weak upper level
disturbance moves eastward across the waters. A small craft
advisory is in effect for the coastal waters from Point Grenville
to Cape Shoalwater out 10 nm through this evening. Small craft
advisories have also been issued for later this morning through
this evening for the western portions of the Strait of Juan de
Fuca. A gale warning has been issued for mid afternoon today
through tonight for the eastern two thirds of the Strait of Juan
de Fuca, and small craft advisories have been issued for Admiralty
Inlet and the Northern Inland Waters for that period as well with
the strongest winds near the east entrance to the strait.

Near gale to possibly gale force winds are possible each overnight
period for the eastern two thirds of the strait through the
Memorial Day weekend and into next week as the onshore flow
pattern continues. Albrecht

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until midnight PDT tonight for Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 3 PM PDT this afternoon for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning from 3 PM this afternoon to 3 AM PDT Saturday for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 2 PM this afternoon to 3 AM PDT
     Saturday for Admiralty Inlet-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory from 11 AM this morning to 8 PM PDT this
     evening for West Entrance U.S. Waters Strait Of Juan De
     Fuca.

&&

$$

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