Small Craft Advisory 157, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
928 PM PDT Sat Jun 24 2017

.SYNOPSIS...High pressure aloft will bring one more very warm day
to Western Washington on Sunday. Much cooler temperatures with
some night and morning clouds will prevail Monday through
Wednesday with an upper trough over the area and and low level
onshore. An upper ridge will move over the area later in the week
for some modest warming.

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.SHORT TERM...An upper ridge currently over the area will shift
inland tonight and Sunday. A thermal trough over the coast will
also shift inland later Sunday. Sunday should be a few degrees
warmer than today for the interior with record highs likely. A
heat advisory remains in effect. The coast will cool 5-10 degrees
as onshore flow develops in the afternoon.

An onshore push will occur Sunday night with low clouds developing
at the coast in the evening and spreading at least partially
inland early Monday morning. There might even be a few showers
over the southern Cascades Monday morning as a short wave clips
the area but most of this is expected to be east of the crest.
Highs will be much cooler on Monday with most areas cooling 15 to
20 degrees. Low clouds should burn back to the coast during the
day.

Moderate to strong onshore flow will continue Monday night and
Tuesday. Low clouds should once again spread inland overnight with
more extensive coverage Tuesday morning and a slower burnoff later
in the day. Highs should cool a few more degrees back to near
normal. Schneider

.LONG TERM...Previous discussion...Progs agree on some ridging
aloft with rising heights Wednesday and Thursday. This change
should translate into some thinning of the marine layer resulting
in a late night/morning clouds, afternoon sunshine regime. For
Friday and Saturday, the progs differ on retaining the building
height trend vs some weak troughing off the coast. Bottom line
here is likely maintaining low level onshore flow and the marine
layer, with afternoon sunshine particularly in the interior and a
bit warmer than average temperatures. Buehner

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.AVIATION...A strong upper ridge axis is squarely over Western
Washington this evening. It will move to the northern Rockies over
the next 24 hours. Light northwest flow aloft will become
southwest on Sunday. Weak low-level offshore flow and a dry air
mass will continue through Sunday morning. Low-level onshore flow
will develop later Sunday, and the low-level air mass will start
to moisten on Sunday night. Clear skies through the day on Sunday,
then marine stratus should make its first appearance near Grays
Harbor as early as Sunday evening.

KSEA...Clear skies and light north wind will persist through
Sunday evening.	Haner

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.MARINE...A somewhat diffuse thermal pressure trough will linger
near the coast until after sunrise on Sunday, leading to weak
low-level offshore flow. The trough will move east of the Cascades
on Sunday afternoon, opening the door to increasing onshore
gradients and wind. UIL-BLI gradient should peak on Monday night,
by which time westerly gales appear likely in the central and
eastern Strait. Cannot rule out gales on Sunday night, thus the
Gale Watch, but the NAM's forecast UIL-BLI gradient of +2 to +2.7
mb on Sunday night is not convincing at that time. Haner

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory until 9 PM PDT Sunday for Bellevue and Vicinity-
     Bremerton and Vicinity-East Puget Sound Lowlands-Hood Canal
     Area-Seattle and Vicinity-Southwest Interior-Tacoma Area.

PZ...Small Craft Advisory until 10 PM PDT this evening for Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From James Island To Point Grenville Out 10
     Nm-Coastal Waters From Point Grenville To Cape Shoalwater
     Out 10 Nm.

     Gale Watch from Sunday evening through late Sunday night for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

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www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html