Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 242148
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
248 PM PDT Sun Sep 24 2017

.SYNOPSIS...A frontal system will bring clouds and a little rain
later tonight and Monday. An upper ridge and low level offshore
flow will bring sunshine and warmer weather in the middle of the
week. A weak front and an upper trough will bring cooler weather
and possibly some showers late in the week.

&&

.SHORT TERM...A frontal system will bring a rain threat to the
area later tonight through Monday evening. The best chance for
rain will be at the coast where rain will be likely Monday.
Chances will be lower inland as the front falls apart. Highs will
be a few degrees cooler Monday with additional cloudiness. An
upper ridge will build over the area Monday night and Tuesday. Any
lingering showers should end Monday evening and clouds should
decrease over the area Tuesday. Highs will return to near normal
Tuesday. The upper ridge will strengthen over the area Wednesday.
At the same time, low level offshore flow will develop as a
thermal trough builds north along the west coast. This will bring
sunny and warmer weather Wednesday. High should warm into the 70s
most areas. Schneider

.LONG TERM...An upper ridge over the area will begin to shift
inland Thursday. A thermal trough just offshore will weaken but
remain in place for another sunny and unseasonably warm day.
Highs will be in the 70s most areas and some locations could reach
the lower 80s. An upper trough and a weakening front will reach
the area Friday for a chance of rain with highs cooling several
degrees. The ECMWF is a bit stronger and wetter with this system
compared to the GFS. The forecast is a blend for now. Fairly
uneventful zonal flow aloft will prevail next weekend. A warm
front might clip the north part of the area Sunday but not much is
expected from this right now. Schneider

&&

.AVIATION...An upper level ridge centered offshore will keep the
flow aloft northerly over the region. The low level flow will
remain weak onshore. Anticipate areas of LIFR CIGs and IFR VSBYs
to dvlp later tonight.

KSEA...MVFR CIGs should develop Monday morning and then persist
into the afternoon. Light northerly winds will become light
southerly tonight.

&&

.MARINE...A warm front offshore heading towards Canada tonight
will cause the flow to back to southerly. This front will move
across British Columbia while weakening on Monday for light
southerly flow over the area. The flow will become light northerly
on Tuesday due to higher pressure over western Canada and lower
pressure over OR. The flow will become more offshore or easterly
on Wednesday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 1 AM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

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


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