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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

FXUS66 KSEW 252228

Area Forecast Discussion
National Weather Service Seattle WA
330 PM PDT Fri May 25 2018

.SYNOPSIS...Onshore surface flow will increase tonight, bringing 
marine clouds inland along with areas of drizzle Saturday. There 
will be fewer marine clouds Sunday and Memorial Day. Next week will 
be a little cooler.


.SHORT TERM...Clouds over the interior have been a little slow 
to clear, but satellite imagery shows significant erosion from 
the edges and the cloud deck has become noticeably thinner in 
the last few hours. The clearing trend should continue into the 
evening. Onshore flow will increase tonight. Westerly gales are 
likely in the strait tonight, and marine stratus will arrive over 
the interior late tonight. The marine layer is likely to be thick 
enough to produce local light rain or areas of drizzle. High 
temperatures Saturday will be in the 60s.

Onshore surface flow will weaken considerably Saturday night and 
Sunday. This will mean fewer clouds and no drizzle on Sunday. With 
plenty of sunshine, temperatures will be higher, with mid 60s on the 
coast and low to mid 70s inland. On Sunday night onshore flow will 
increase again, so the marine layer will move over inland areas. 
Monday will be cloudy in the morning with afternoon clearing. Highs 
will be in the low 70s inland to near 60 on the coast. Burke

.LONG TERM...Tuesday looks similar to Monday. Something of a change 
in the patten occurs for the Wednesday through Friday period, as an 
upper trough sets up over the region. Heights will be lower, and 
there will be a chance of showers at times. Currently the best shot 
at a little rain are Wednesday and again Thursday night. Highs will 
be in the 60s all three days. Burke 


.AVIATION...The tail end of a weak upper trough will brush by
Western Washington early this evening. This will strengthen low-
level onshore flow and reinforce the moist and stable low-level
marine layer. Expecting fairly widespread coverage of cigs at or 
below 020 over the lowlands in the hours after sunrise on 
Saturday. Moderate southwest flow aloft will become weak 
northwesterly late tonight. Above the marine layer, the air mass
will be dry and stable. 

KSEA...Surface wind for most of this evening will have a northerly
component, but then a turn to light southerly wind is expected
sometime between 05z and 08z (10 pm and 1 am). More marine clouds
on Saturday morning, with cigs below 020 expected. Scattering will
hold off until about 20z-21z on Saturday. Haner


.MARINE...Moderate to strong onshore flow will continue through 
the Memorial Day weekend and into the middle of next week,
following the familiar diurnal cycle in which westerlies through
the Strait peak from late afternoon through the evening hours. 
The strongest onshore flow will occur this evening, when westerly
gales are expected over the central and eastern Strait. Small 
Craft strength westerlies are forecast in the Strait all other 
evenings for the next week. Gales are possible any evening from
Sunday through Wednesday. Haner


PZ...Small Craft Advisory until 9 PM PDT this evening for Coastal 
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 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 until 3 AM PDT Saturday for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands.