Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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684
FXUS66 KSEW 190417
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
915 PM PDT SUN SEP 18 2016

.SYNOPSIS...A cool unsettled weather pattern will bring a few
showers and cool temperatures to the area through Wednesday. The
upper low will move off to the east of the area Thursday. A weak
front will reach the area late in the week.

&&

.SHORT TERM...A few showers at times and some partial clearing will
be the weather pattern for the area for the first half of the week.
Showers this evening were mainly on the north coast and from near
the Snohomish/Skagit county line north.  Skies were mostly clear this
evening in the metro area for a nice moonrise. The upper low will
settle in over the area Monday night through midweek as it weakens.
Skies will generally be partly cloudy through the period and there
will be a small chance of showers that can pop up any time of day
as difficult to time features rotate around the circulation. Temps
will warm into the 60s during the day and will fall mainly into the
40s at night.

.LONG TERM...Models are generally consistent in moving the upper
low off to the east and southeast on Thursday. The ECMWF keeps the
low near the area a bit longer than the GFS. Still, Thursday
appears that it will be the driest day of the next several as we
fall between the departing low and an incoming frontal system.

The 12Z long term models have gone back to splitting the next
frontal system as it moves into the area and weakening it over the
forecast area. The models then show a very broad ridge building
across the eastern Pacific and western North America next Saturday
and Sunday as weak impulses move across the area. Will keep clouds
and a chance of a little rain at times in the far extended along
with milder temperatures. Albrecht

&&

.AVIATION...Westerly flow aloft over Western Washington will
continue tonight and Monday. A weak front will move into the
forecast area on Monday. The air mass will be moist in the low
levels tonight, then become moist to about 10,000 feet and weakly
unstable on Monday.

Ceilings generally in the 6000-9000 foot range this evening with
some local 2000 foot ceilings along the coast. Little change
overnight. Ceilings will lower into the 2500-4000 foot range Monday
morning with areas of light rain as the weak front moves into the
area. Conditions will improve later in the afternoon.

KSEA...South to southwest winds 4-8 kt increasing to 6 to 12 knots
on Monday. Ceilings aoa 5000 feet into early Monday morning.
Ceilings lowering to near 3500 feet with occasional light rain later
Monday morning. Conditions will improve late in the afternoon. Felton

&&

.MARINE...Light onshore flow will continue through Monday with a
weak front moving through the northern portion of the waters Monday
morning. A weak surface low will develop over the coastal waters
Monday night, then dissipate on Tuesday. Light onshore flow will
develop Wednesday and continue through Thursday. A front could move
into the forecast area on Friday. Felton/McDonnal

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...None.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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