Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 252149
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
300 PM PDT Mon Sep 25 2017

.SYNOPSIS...A weak front over the area will dissipate tonight. Dry
air will shift over the region as a ridge builds into the area on
Tuesday. The air will warm as low level offshore flow develops on
Wednesday. Thursday will also be a warm sunny day. A cold front will
reach the area Friday and unsettled weather is likely next weekend.

&&

.SHORT TERM...A weak front is stalled near the coast and it will
probably be drippy into the evening hours there. The areas of light
rain or shower activity will dry up tonight as the front fizzles out
and high pres begins to build into the area. An upper ridge will
build into the region Tuesday and Wednesday--and low level offshore
flow will boost the temps midweek. Thursday should also be sunny and
warm before onshore flow develops late in the day. High temps should
top 80 degrees in the warmest spots around Western Washington Wed
and Thu.


.LONG TERM...Onshore flow will develop Thursday night ahead of a
front that should reach the area on Friday for some rain. The precip
could hold off til afternoon or evening and the upper trough doesn`t
reach Western Washington til Saturday morning. The weekend should be
cool, showery and unsettled behind the front. A stronger front and
deep low was in the models out around Sunday or Monday of next week,
but the 12z runs are different and what will happen out around a
week from now is rather uncertain.

&&

.AVIATION...An upper level ridge centered offshore will keep the
flow aloft northerly thru tonight. Weak low level southerly flow
will become flat overnight. In general, expect areas of IFR CIGs/
MVFR VSBYs.

KSEA...VFR. There might be a brief period of MVFR CIGs this
afternoon but MVFR CIGs are more likely Tuesday morning. Expect VFR
conditions Tuesday afternoon. Light southerly winds will become
light and variable overnight, and then northerly 5-10 knots Tuesday
afternoon.

&&

.MARINE...Weak southerly flow will become light and variable
overnight. Expect the flow to become light northerly on Tuesday due
to higher pressure building over British Columbia and lowering
pressure over OR. A thermally induced trough of low pressure along
the WA coast will cause the flow to become easterly early Wednesday.
Expect onshore flow to return on Friday.

&&

.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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