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

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

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


Sew watches/warnings/advisories...
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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