Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 172247 CCA
AFDSEW

Area Forecast Discussion...corrected
National Weather Service Seattle WA
330 PM PDT Thu Aug 17 2017

.SYNOPSIS...Seasonable summer weather will continue through
Friday with morning clouds and afternoon sunshine. A weak system
will brush the area Friday bringing slightly cooler conditions and a
chance of light rain or drizzle mainly to the north coast and north
Cascades. High pressure will begin to rebuild over the region Sunday
afternoon, reinforcing dry and warmer weather into early next week.

&&

.SHORT TERM...Stratus has burned back to the central Washington
coast with a few lingering clouds over the western slopes of the
Cascades this afternoon. Onshore flow will bring stratus back to
much of the interior late tonight into early Friday morning. A
weakening frontal system will pass to the north of the area Friday
with resulting in a slight chance of light precipitation mainly over
the North Coast in the morning and over the North Cascades during
the afternoon. More than anything this feature will likely bring
little more than increased mid and high level clouds especially over
the northern half of the area Friday. Low clouds will return again
late Friday night into Saturday with afternoon clearing. Flow aloft
will remain westerly Saturday as the upper level ridge over the
Eastern Pacific remains slow to rebound. Temperatures should look
pretty similar to Friday with highs in the upper 60s to mid 70s over
parts of the interior.

.LONG TERM...The dirty ridge and zonal flow over the Eastern Pacific
will start to break down as an upper level trough digs into the Gulf
of Alaska from the Bering Sea Sunday. This will result in the upper
level ridge amplifying downstream of the approaching trough. Heights
will begin to rise over Western Washington Sunday afternoon through
Monday. Rising heights and warming aloft will help high temperatures
creep back up into the upper 70s to low 80s over the interior on
Monday and Tuesday with mostly sunny to sunny skies. The sky
forecast continues to look good for the eclipse on Monday. The ridge
axis will shift east Tuesday ahead of a weak upper level trough
approaching the region from the west. Medium range models continue
to differ on the timing and strength of this system hinting at a
chance of showers Wednesday afternoon into Thursday.

&&

.AVIATION...The upper level ridge will move east overnight,
allowing an upper level trof to approach from the northwest. The
main impact will be a deeper marine layer. Westerly flow aloft and
low level onshore flow will continue. Areas of MVFR CIGs will
become wdsprd across much of the lower elevations by early tomorrow
morning.

KSEA...VFR conditions will prevail through this evening. Low clouds
(MVFR CIGs) will return late tonight and will probably be slower
to lift tomorrow. Light westerly winds will become northerly late
this afternoon. Expect winds to become light southerly late
tonight before veering to westerly Friday afternoon.

&&

.MARINE...
A typical August pattern will prevail through the middle of next
week. Expect onshore flow of varying strength to persist due to
higher pres offshore with lower pres east of the Cascades. There
is a possibility that westerly winds could reach gale force over
the central and eastern Strait of Juan de Fuca Friday night.
Therefore, a Gale Watch was issued for these waters.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisories are in effect for the central and
 eastern Strait of Juan de Fuca.

 Gale Watch in effect from Friday evening through late Friday
 night for the central and eastern Strait of Juan de Fuca.

&&

$$

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html


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