Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 291534
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
834 AM PDT MON AUG 29 2016

.SYNOPSIS...A front will bring a little rain Tuesday night and
Wednesday. An upper trough will cross the Thursday and Friday for
some showers. Weak high pressure aloft will bring drier and
slightly warmer weather next weekend.

&&

.SHORT TERM...An upper trough will dig between 130W and 140W
today. This will back the flow aloft over Western Washington and
hold a frontal system off the coast. The upshot is a dry day
today for most of the area with highs warming several degrees. The
upper trough and associated frontal system will move slowly
towards the area Tuesday but rain will probably remain off the
coast until the evening. Low level onshore flow will increase for
a bit more cloudiness and a few degrees of cooling. The front
eventually pushes into the interior on Wednesday. There are some
model timing differences so confidence when the rains will
develop is not high but it should get here eventually. Highs will
cool another few degrees with the upper trough and front.
Schneider

.LONG TERM...Previous discussion...the mid range guidance concurs
on nudging the offshore upper trough inland Thursday and Friday.
This system will offer some showers along with cooler than first
of September high temperatures. The trend is also for the current
high amplitude flow pattern across the north Pacific and North
America to become more zonal.

As we head into the coming holiday weekend, the progs tend to
differ. The Canadian and ECMWF are in general agreement that the
Pacific NW will have slowly rising 500 millibar heights and a drying
trend. The GFS offers an incoming flat upper trough. The current
forecast maintaining a threat of showers into the weekend is okay
for now. Stay tuned as these weather feature details become more
clear. Buehner

&&

.AVIATION...An upper level trough is just offshore with southwest
flow aloft over the region. The air is stable with areas of low
level moisture this morning. The areas of morning low clouds and
patchy fog will give way to mainly scattered mid and high clouds
by midday.

KSEA...A patch of morning low clouds was creeping into Sea Tac
at 8am, that may push over the runways for a couple hours but
then burn off pretty quick. Scattered mid and high clouds with a
light and variable wind for the afternoon and tonight.

&&

.MARINE...A weak front will stall over the offshore waters
today and tonight. Winds will remain below small craft strength
over the coastal waters, then reach small craft strength Tuesday
in at least the outer coastal waters before the front reaches the
coast Tuesday evening. The front will weaken and push through the
inland waters Tuesday night with winds likely to stay below 20 kt.
Another front will reach the area late Thursday or Friday. This
system could be strong enough for another round of small craft
advisory winds over the coastal waters. Felton

&&

.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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