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330
FXUS66 KSEW 011005
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
305 AM PDT Sun Sep 1 2024

.SYNOPSIS...
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An upper level ridge will maintain warm and dry
conditions today. An incoming shortwave trough will bring a
return to onshore flow and cooler temperatures on Monday, as well
as a few showers or isolated thunderstorms over the Cascades.
A ridge will rebuild over the area midweek for a return to dry and
warmer conditions.
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.SHORT TERM /TODAY THROUGH TUESDAY/...
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Stratus is creeping inland
from the coast early this morning as low level onshore flow
increases ahead of a weak upper trough that will move onshore
over Oregon on Monday. The marine push will be initially pretty
shallow today with high temperatures across the interior a smidge
cooler than yesterday while coastal areas will be 15 to 20 degrees
cooler. The marine layer will deepen substantially on Monday with
a mostly cloudy and considerably cooler day expected for most of
the Western Washington lowlands. Increasing southerly flow aloft
along with some elevated instability will lead to a slight chance
of thunderstorms over the southern Cascades by early Monday and
the threat will spread north along the spine of the Cascades into
Monday afternoon. Onshore flow and cool conditions will continue
into Tuesday, but upper ridging will begin to rebuild just
offshore as signs point toward a noteworthy warming trend heading
into the beginning of the long term forecast period.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Just in time for
students heading back to school, an upper ridge axis will
strengthen over the region and the low level flow will turn
offshore once again. Coastal as well as interior lowland areas
will warm back into the upper 70s to mid 80s Wednesday into
Thursday under plenty of sunshine. The ridge weakens somewhat and
the flow turns onshore heading into the end of week. This will
cool temperatures a bit, but ensembles are in relatively good
agreement that dry conditions and above normal temperatures will
remain in place into Saturday. 27
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&&

.AVIATION...
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Western Washington remaining on the back side of an
upper level ridge through Monday. Upper level low off the Southern
Oregon coast today moving inland Monday. Southerly flow aloft into
Monday. In the lower level increasing onshore flow with thermally
induced trough moving east of the Cascades.

Stratus along the coast, over the Lower Chehalis Valley into the
southern portion of the Hood Canal early this morning. Stratus
will not get much further inland and will retreat back to the
coast by 18z. Ceilings with the stratus below 1000 feet with local
visibility 3-5sm in fog. Stratus moving back inland tonight
reaching the Puget Sound area 09z-12z with ifr ceilings.

KSEA...Clear skies. Light wind becoming northwest 4 to 8 knots
around 18z. Wind switching to southwest around 06z with ifr
ceilings arriving 09z-12z. Felton
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&&

.MARINE...
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Increasing onshore flow today as thermally induced
surface trough moves into Eastern Washington. Onshore flow
pattern continuing into Tuesday. Another thermally induced trough
moving northward along the coast Wednesday with offshore flow
Wednesday and Thursday.

Small craft advisory westerly winds in the Central and Eastern
Strait of Juan de Fuca tonight and again Monday night. Felton
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.FIRE WEATHER...
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An upper level ridge will continue to promote warm
and dry conditions today. The low levels of the atmosphere remain
quite dry in the Cascades and Cascade valleys and relative
humidity values could drop as low as 15-20 percent in the central
and southern portions of the Washington Cascades and mountain
valleys. Conditions are unstable with mid-level Haines reaching
6. Fuels in zone 659 have dried to where ERCs now exceed the 90th
percentile. A Red Flag Warning remains in effect for the central
Cascades from early this morning through this afternoon. Moist
and cool onshore flow will begin to develop this evening,
providing relief to the critical fire weather conditions.

With fuels drying region-wide, we will have to watch the
potential for some isolated thunderstorms over the Cascades on
Monday. While storms are not expected to be widespread enough for
Red Flag conditions, little precipitation is expected and there is
some potential for new fire starts.

LH/27
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&&

.SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Red Flag Warning until 5 PM PDT this afternoon for West Slopes
     of the Central Cascades Generally above 1500 Feet.

PZ...None.
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&&

$$