970
FXUS66 KSEW 291722
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
1022 AM PDT Sat Jun 29 2024

.SYNOPSIS...Southwesterly flow aloft today with upper level ridge
well to the east and a weakening front moving into the area late
in the day. Front dissipating tonight. Upper level trough moving
through Sunday keeping a chance of showers in the forecast. Upper
level ridge building offshore Monday will drift slowly eastward
moving over the area Thursday and Friday. Warmest day of the year
possible Friday.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...Forecast remains on track
this morning with some variable high clouds streaming through the
area. No updates required, and the remainder of the previous short
term section follows.

Middle and high level clouds continuing to stream over the
area this morning. Clouds thickening up this afternoon with the
front close enough for a chance of showers west of Puget Sound in
the afternoon. Air mass somewhat unstable over the Cascades and
with increasing middle level moisture ahead of the front could see
a shower there as well in the afternoon. Highs in the mid 60s
along the coast and upper 60s to mid 70s inland.

What is left of the front moving inland tonight giving most of the
area a chance of showers this evening. With the front lifting to
the northeast the chances for showers will linger over the
northern portion of the area after midnight. Like this morning,
with plenty of cloud cover low temperatures will be mild, in the
mid 50s to lower 60s.

Weak upper level trough behind the front moving through Sunday
keeping at least mostly cloudy skies and a chance of showers in
the forecast. Trough axis moving through midday. Increasing
onshore flow behind the trough axis with a convergence zone
developing over Snohomish county in the afternoon. Little change
in the high temperatures with mid 60s coast and upper 60s to mid
70s inland.

Upper level trough continuing to move east Sunday night. Chance of
showers becoming confined to the Cascades and the convergence zone
over Snohomish county in the evening. Convergence zone will last
into the morning hours Monday. Outside of the Cascades and
convergence zone some clearing Sunday evening but with the low
level onshore flow clouds will fill back in overnight. Lows in the
50s.

Weak trofiness over Western Washington Monday morning with 500 mb
heights rising in the afternoon as an upper level ridge begins to
build offshore. The combination of weak trofiness and a dying
convergence zone will keep a chance of showers in the morning
from about Snoqualmie Pass northward. Morning clouds over the
lowlands giving way to afternoon sunshine with the subsidence from
the upper level ridge building taking care of the morning marine
layer. Highs once again in the mid 60s along the coast and upper
60s to mid 70s inland.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Extended models in good
agreement with what looks like the beginning of the summer pattern
setting up over the Pacific Northwest through the period. Upper
level ridge offshore slowly drifting east ending up over Western
Washington Thursday and Friday. Low level onshore flow Tuesday and
Wednesday weakening Thursday and Friday. Low level flow never
really turns offshore late in the week. 500 mb heights peaking
around 590 dms Thursday into Friday. 850 mb temperatures in the
single digits Tuesday warming to near plus 20C by Friday. With
temperatures aloft this warm even without offshore flow warmest
locations will be pushing 90 degrees Friday. Areas of morning
clouds with afternoon sun Tuesday and Wednesday. Mostly sunny
Thursday and Friday. Highs Tuesday in the mid 60s along the coast
with upper 60s to mid 70s inland. Highs a couple of degrees warmer
Wednesday and Thursday. By Friday, highs in the 70s along the
coast and upper 70s to near 90 inland. Felton

&&

.AVIATION...Flow aloft today will become southwesterly ahead of a
shortwave trough approaching from the west today (ridging also
located east of the Cascades). A weak front will bring the chance of
showers today over the Olympics, as well as along the Cascade crest.
Activity is expected to move in a northerly direction. Brief heavy
downpours may temporarily reduce VIS/CIGs and produce gusty/variable
winds (in and around terminals). A few terminals are seeing easterly
winds off the Cascades this morning. As the trough approaches,
expect the winds to become westerly to southwesterly throughout the
day at 6 to 10 kt. CIGs will begin to fill in late this
morning/afternoon around 10,000 ft, and drop to MVFR as moisture
works its way inland from the coast. There is a slight chance of IFR
for terminals along and west of Puget Sound Sunday morning that will
scatter later in the day Sunday.

KSEA...VFR conditions through most of Saturday. Slight chance of
showers from 17Z-02Z Sunday (most of the activity may stay west of
the terminal). CIGs gradually lowering to MVFR after 04Z Sunday
(slight chance of IFR if enough moisture mixes down). Few easterly
winds this morning at 6 kt will become westerly late this
morning/afternoon, then becoming southerly after 02Z Sunday.

HPR

&&

.MARINE...A weak frontal system will move through the
coastal waters today reaching the inland waters late. Showers will
be possible Saturday afternoon and evening (a few may be heavy
enough to reduce visibilities over the east Strait of Juan de Fuca
and Puget Sound waters). The front will dissipate over the inland
waters tonight. High pressure builds offshore Sunday, and will send
a few pushes through the Strait of Juan de Fuca through early next
week. There`s a slight chance west winds may exceed 20 kt Sunday
afternoon/evening in the central/east Strati of Juan de Fuca
sections (better chance for Monday).

Seas will reach 4 to 6 feet today, and remain at 4 to 6 feet through
the forecast period.

Felton/HPR

&&

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

$$