Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 272146
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
250 PM PDT Sat May 27 2017

.SYNOPSIS...A strong upper level ridge will remain over the
Pacific Northwest through the Memorial Day weekend, with sunny
skies and afternoon high temperatures well above normal.
Increasing onshore flow will cool temperatures starting on Tuesday
and southerly flow aloft will bring a chance of showers to the area.
Weak disturbances may bring a chance of showers to the area into the
end of the week.

&&

.SHORT TERM...Shallow marine stratus is over the coastal waters and
beaches but it is sunny and warm elsewhere. Temps aloft will warm a
bit more and the sunny warm weather will continue into the first
part of the week. The marine layer should be deepening Monday night
and Tuesday, and an upper trough will bring southerly flow aloft
with an increasing chance of showers and a few thunderstorms to the
area by Tuesday night.

.LONG TERM...A chance of showers will linger with cooler temps and
marine air mass. The best chance of showers may turn out to be
Tuesday night and Wednesday as a shortwave trough moves through the
area--the 12z GFS is wetter than the ECMWF. Then, for the rest of
the week the showers look pretty few and far between except perhaps
on Friday, but pops are still pretty low for now and the extended
forecast hasn`t been changed much.

&&

.AVIATION...A ridge of high pressure will remain over the region
through Sunday. Light variable or southerly flow aloft. Air mass dry
except moist near the surface toward the coast. KHQM may have
periods of IFR fog and low stratus later tonight/Sunday morning.
Otherwise IFR skies with light northerly flow easing this evening,
the picking up to 7-8 kt after 18z Sunday.

KSEA...VFR skies. North to northwest winds up to 9 kt. Light
variable or northeast winds after 04z.

&&

.MARINE...Higher pressure offshore with lower pressure inland will
result in weak onshore flow today. The flow will become nearly flat
or neutral tonight before becoming onshore again Sunday afternoon.
Small craft winds could briefly develop in the central and eastern
strait by Sunday evening.

Strengthening high pressure offshore along with lowering pressure
east of the Cascades will result in stronger onshore flow Monday and
Tuesday. This will lead to the likelihood of gale force winds over
parts of the Strait of Juan de Fuca Monday night, and possibly
Tuesday. Stronger flow off the Pacific along with a 15-20 degree
temperature difference between the WA coastal beaches and the
interior WA lowlands Monday afternoon will only increase the
potential for gale force winds over the Strait of Juan de fuca.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$

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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