Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 260349
AFDSEW

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

.SYNOPSIS...A strong upper ridge will build over the area Tuesday
and remain through Thursday. The air mass 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...Radar returns have noticeably decreased and the weak
front that was along the coast this afternoon has now dissipated. An
upper ridge will begin building over the area tonight and heights
will continue to build Tuesday. The ridge will remain over the
region through Thursday.

A thermally induced trough of low surface pressure will develop on
the coast and the resulting low level offshore flow will boost the
temperatures midweek. Highs will rise from the low 70s Tuesday to
near 80 Thursday. Skies will clear during the day Tuesday and both
Wednesday and Thursday will be sunny. Burke

.LONG TERM...Previous discussion...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...Isolated showers in the interior will diminish this
evening as an upper level ridge shifts inland. The low level air
mass will remain moist and stable with MVFR to IFR ceilings
expected overnight into Tuesday morning. The air mass will dry
out Tuesday afternoon for VFR conditions. 33

KSEA...Light/variable wind tonight becoming northerly 09-12z. MVFR
cigs possible tonight with moist low levels. VFR conditions
expected Tues afternoon. 33

&&

.MARINE...Light variable winds over the waters tonight with weak
pressure gradients over the region. The flow will turn northerly
on Tuesday then offshore by midweek as a thermal trough forms
along the coast. A weak cold front will cross the area on Friday.
33

&&

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

$$

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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