FXUS66 KSEW 231555

Area Forecast Discussion
National Weather Service Seattle WA
855 AM PDT Wed Aug 23 2017

.SYNOPSIS...Expect cooler conditions today with onshore flow. A
weak cold front will bring light showers to the coast today. The
trailing upper level trough will cross the region late tonight
into Thursday. An upper level ridge will build quickly into the
region on Saturday with above normal high temperatures through


.SHORT TERM...An onshore push and approaching trough will help
cool down Western Washington a good 5-10 degrees today compared
to yesterday. Expect highs mainly in the 70s today with 60s along
the coast. Stratus should break up in the interior for partly
sunny skies this afternoon. A weak front will bring isolated to
scattered showers to the coast, although precip amounts look very
light (less than 0.10"). The trough axis will swing through late
tonight into Thursday morning with isolated showers possible in
the interior and Cascades. Weak troughing over the Pac NW will
keep temperatures near normal through Friday. Onshore flow will
prevail with dry weather expected. 33

.LONG TERM...Previous discussion...Extended models are in good
agreement with a strong upper level ridge building quickly over
the area from the southeast on Saturday. Highs warming into the
70s to mid 80s. The ridge will remain over the area Sunday and
Monday before shifting slightly east on Tuesday. 500 mb heights
with the ridge near 590 dms. Low level flow turns offshore on
Monday making it the warmest day in the extended forecast. Warmest
locations on Sunday will get into the lower 90s with more 90s on
Monday south of Seattle. No records highs forecast at this time
with the highs on Sunday and Monday just a few degrees short of
the records. With the ridge shifting slightly east on Tuesday and
the low level flow turning onshore during the day will go for a
little cooler high temperatures. Felton


.AVIATION...Southwest flow aloft over Western Washington this
morning will continue through tonight as an upper trough
approaches the Pacific Northwest. Strong low level onshore flow
developed Tuesday evening, then eased overnight and will increase
again this evening. The air mass is moist below 3000-4000 ft.

Marine stratus is giving fairly widespread low-end MVFR and local
IFR conditions to Western Washington at 8 am. The clouds should
scatter out over the interior lowlands late morning, and they will
probably form again tonight.

KSEA...Southerly wind 4-10 kt veering to northwest 6-12 kt late
this afternoon, then becoming southerly again after sunset. The
BKN-OVC stratus layer should scatter out around 18Z. McDonnal


.MARINE...A weak upper trough will approach British Columbia and
the Pacific Northwest today and tonight, then continue inland
Thursday, resulting in continued strong onshore flow across
Western Washington. Gale westerlies are likely again tonight in
the central and eastern Strait of Juan de Fuca, with small craft
advisory winds in the adjacent Admiralty Inlet and Northern Inland
Waters. Weaker onshore flow will continue Friday through this
weekend, as high pressure remains off the coast with lower
pressure east of the Cascades. McDonnal


PZ...Gale Warning from 3 PM this afternoon to 5 AM PDT Thursday for
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 3 PM this afternoon to 5 AM PDT
Thursday for Admiralty Inlet-Northern Inland Waters
Including The San Juan Islands.




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