Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 281600

Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT Sun May 28 2017

.SYNOPSIS...An upper ridge over the area will shift inland through
Memorial Day. Onshore flow will increase Monday and Tuesday as the
coastal marine layer deepens and intrudes farther inland each
morning. An upper trough and southerly flow aloft will bring an
increasing chance of showers Tuesday and Tuesday night. Weak
disturbances will keep clouds and a chance of showers in the
forecast at times into the end of the week.


.SHORT TERM...Marine stratus made it a notch farther this morning
and on Monday there will be areas of morning low clouds and patchy
fog into Puget Sound and up through the San Juans. Temps on the
coast today will only be in the lower 60s under stratus that
probably wont burn back all the way to the ocean beaches. Inland
highs should still make it well into the 80s, and Seattle ought to
be about the same as yesterday before temps fall off Monday and
Tuesday as the marine layer deepens and the well timed warm streak
ends. There will probably be a few towering CU over the mountains
today and again Monday afternoon, but the best chance of showers
will come Tuesday or Tuesday night as a shortwave trough arrives and
southerly flow aloft increases.

.LONG TERM...Extended models in good agreement for the first
couple of days with the upper level trough offshore pushing
shortwaves over the area at times Wednesday and Thursday. This will
keep at least a chance of showers in the forecast. Model solutions
start to diverge on Friday with the GFS building a flat ridge over
the area while the ECMWF keeps a trough over Western Washington. The
ECMWF does try to build a ridge over the area on day 8. Current
forecast splits the difference in the models with a chance of
showers continuing on Friday with just a chance of showers over the
Cascades on Saturday. High temperatures will return back to near
normal with 60s common through the extended period. Felton


.AVIATION...A ridge of high pressure will remain over the region
through Monday, then slowly begin to shift inland. Light south to
southwest flow aloft.  Light onshore flow will gradually increase
tonight through Monday, then become strong onshore Tuesday.
Meanwhile, widespread IFR CIGs over the coast and parts of the SW
interior/far south Puget Sound will lift into the MVFR category
range by afternoon. IFR stratus and fog will push further inland
late tonight and Monday morning, likely reaching the KSEA terminal
and possible the KBFI and KPAE terminals in addition to KHQM, KCLM,
and KOLM. This should again mostly burn off by midday, except
perhaps last longer at KHQM. It will become slightly unstable this
afternoon/evening with towering cumulus over the Cascades, but
thunderstorms are not expected to affect any terminals today or

KSEA...VFR with light northerly winds through this evening. Winds
will become light and variable late tonight, the light south wind to
5k after 10z. IFR stratus now appears likely 11-17z Monday morning,
then quickly burning off by midday. Will make this adjustment in the
18Z TAF issuance after reviewing latest guidance. dtm


.MARINE...High pressure offshore along with lowering pressure east
of the Cascades will result in strengthening onshore flow through
Tuesday. This will lead to the potential for gale force winds over
parts of the Strait of Juan de Fuca tonight, Monday and Tuesday.
Gale force winds appear likely tonight with a gale warning in effect
but there is some uncertainty in the timing. It could happen as
early as 8 PM PDT tonight or as late as 1 AM Monday. Small craft
winds will prevail the Strait through Tuesday, reaching Gale or near
Gale force during the evening and overnight hours. Small craft winds
are also possible in waters adjacent to the east entrance to the
Strait as well as the west entrance.

A strong marine Push on Tuesday could potentially bring more
widespread small craft winds to other interior waters including
Puget Sound. Winds may pick up suddenly as the marine push develops.
There is also a threat of Thunderstorms Tuesday.  Forecasts should
be monitored. dtm


PZ...Small Craft Advisories are in effect for the Strait of Juan de
Fuca, Northern Inland Waters, and Admiralty Inlet.

 Gale Warning in effect from this evening through late tonight for
   the central and eastern Strait of Juan de Fuca beginning at 6 pm.



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