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fxus66 ksew 231037 
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Area forecast discussion 
National Weather Service Seattle Washington 
337 am PDT Sat Jun 23 2018 


Synopsis...an offshore upper ridge will move to the coast today, 
gradually breaking up the clouds over western Washington. The 
ridge will bring sunny and warmer weather on Sunday. An upper 
trough will arrive Monday for a chance of showers and cooler 
weather. Tuesday and Wednesday will be partly to mostly sunny, 
then another upper trough will be over the area late in the week. 


&& 


Short term...we have northwest flow aloft over western 
Washington early this morning ahead of an offshore upper ridge 
that is moving inside of 130w. Low level onshore flow has become 
light, but there is still quite a bit of moisture in the lower 
5000 ft of the atmosphere. A weak Puget Sound convergence zone 
developed Friday evening, producing a drizzle storm as it moves 
slowly south. At 3 am it had moved south of SeaTac and starting to 
dissipate. 


The upper ridge will continue its eastward progression, moving to 
the Pacific northwest coast this afternoon and across the Cascades 
tonight. Onshore flow will continue to diminish and the marine 
layer will gradually dry during the day, but for much of western 
Washington -- and that most likely includes the greater Seattle 
metropolitan area -- the stratocumulus layer will only scatter 
out during the afternoon. Highs today will be a little above 
normal, ranging from the upper 60s to the lower 80s across The 
Lowlands. The upper ridge will bring a sunny and somewhat warmer 
day on Sunday as it moves across eastern Washington, with highs in 
the mid 60s to lower 70s at the coast and in the mid 70s to lower 
80s inland. 


A cold front will move across western Washington from the offshore 
waters Sunday night, followed by an upper trough on Monday. It 
will bring some showers, but precipitation amounts will generally 
be light. There should also be a little sunshine on Monday, and 
highs will be mainly 60 to 70. Mcdonnal 


Long term...the upper trough axis will move east of the Cascades 
Monday night, leaving zonal and weakly cyclonic flow over western 
Washington on Tuesday. The day will probably start mostly cloudy 
with a few residual showers, becoming mostly sunny in the 
afternoon. Strictly zonal flow will continue Wednesday -- which 
should allow for a mostly sunny day -- and then another upper 
trough will bring a chance of showers Wednesday night through 
Friday. Mcdonnal 


&& 


Aviation...upper level ridge building into the area today will 
shift into eastern Washington later tonight and Sunday. Westerly 
flow aloft becoming southwesterly Sunday morning. In the lower 
levels onshore flow today weakening tonight with decreasing low 
level moisture beginning this afternoon. 


Convergence zone moving into the central Cascades at 10z. Low level 
moisture left behind by the convergence zone with areas of ceilings 
below 1000 feet between kpae and ksea until around 15z. For the 
remainder of the area scattered to broken cloud layer around 1500 
feet with a broken to overcast later around 2500 feet. Ceilings 
improving after 15z with ceilings in most areas 2000-3000 feet by 
19z and 3500-4500 feet around 21z. Cloud deck scattering out in the 
late afternoon and evening hours. Stratus deck reforming early 
Sunday morning with ceilings returning to the 1000-2000 foot range 
10z-15z. 


Ksea...ceilings remaining below 1000 feet until around 15z with 
visibilities 1-3sm at times in light rain/drizzle. Improving trend 
later this morning with ceilings near 2000 feet by 19z and above 
3000 feet by 21z. Clouds scattering out late afternoon. Variable 
winds 5 knots or less becoming northwesterly 4 to 8 knots late 
afternoon. Felton 


&& 


Marine...onshore flow will continue with westerlies in the Strait 
of Juan de Fuca--rising to at least 20-30 kt each evening, but 
possibly reaching gale force for a few hours. A cold front will 
reach western Washington Sunday night ahead of the next upper 
trough. 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory until 3 am PDT Sunday for central U.S. 
Waters Strait of Juan de Fuca-East Entrance U.S. Waters 
Strait of Juan de Fuca. 






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