679
FXUS66 KSEW 301101
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
401 AM PDT Sun Jun 30 2024

.SYNOPSIS...Weak upper level trough over Western Washington today
with a convergence zone over mainly Snohomish county. Trough moves
east tonight and convergence zone dissipates Monday morning. Upper
level ridge building offshore Monday will slowly move east for the
remainder of the week ending up near Western Washington by late in
the week.

&&

.SHORT TERM /TODAY THROUGH TUESDAY/...Satellite imagery shows
cloudy skies over Western Washington early this morning. Doppler
radar indicating showers over the Central and Northern Cascades as
well as over Whatcom county. With the cloud cover temperatures
were on the mild side at 3 am/10z, in the upper 50s to mid 60s.

Weak upper level trough over Western Washington today. Convergence
zone developing over Snohomish county this morning with the
convergence zone continuing into the afternoon hours. Main story
today will be the cloud cover. With the weak trough will have a
slight chance of showers for most of the lowlands in the morning.
By afternoon showers chances becoming confined to the convergence
zone and the Cascades. Air mass unstable enough over the North
Cascades for a slight chance of a thunderstorm this afternoon.
Highs today in the mid 60s along the coast and upper 60s to mid
70s inland.

Upper level trough moving east tonight but the weak convergence
zone will remain intact into the early morning hours. Showers
chances pretty much confined to the convergence zone into early
Monday morning. Some clearing early but with increasing low level
onshore flow cloud cover increasing again overnight. Lows in the
50s.

Upper level ridge building offshore Monday. Weak shortwave
rippling down the back side of the ridge nicking the Northern
portion of the Cascades keeping a chance of showers in the
forecast for that location. For the remainder of the area morning
clouds will give way to afternoon sunshine. Highs in the mid 60s
coast and upper 60s to mid 70s inland.

Upper level ridge slowly starting to move east Monday night into
Tuesday. Low level onshore flow continuing through Tuesday keeping
the late night and morning clouds with afternoon sunshine forecast
going through Tuesday. With the onshore flow highs Tuesday will be
similar to Monday, mid 60s coast and upper 60s to mid 70s inland.
Lows Tuesday morning in the 50s.

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models in good
agreement with the upper level ridge continuing to move east
Wednesday. The ECMWF brings the ridge over Western Washington
Thursday with the ridge remaining over the area into Saturday. The
GFS keeps the ridge offshore Thursday through Saturday. Both
models do not turn the low level flow offshore going to more flat
gradients beginning Thursday. Slow warming trend through the
period with highs Wednesday in the mid 60s along the coast and 70s
inland warming to the mid 70s to lower 80s along the coast and
upper 70s to near 90 inland Saturday. Ensembles show a big spread
in the solutions for the high temperature Saturday. Model blend
puts highs in the mid 70s along the coast and mid 70s to upper 80s
inland. Ensemble means off both the GFS and ECMWF were a few
degrees warmer then the blend. Given the possible HeatRisk issues
have gone with the warmer ensemble mean highs for Saturday. Felton

&&

.AVIATION...A weak upper level trough remains over the region today
with west to northwest flow aloft. The air mass is moist with
widespread IFR and low MVFR ceilings this morning. Ceilings are
expected to gradually lift by afternoon with most areas returning to
VFR near or after 22Z. Areas of MVFR will redevelop by early Monday
A.M.

KSEA...IFR or occasional LIFR ceilings are expected to linger
through mid-morning before gradually lifting to VFR 20Z-22Z. Surface
winds S/SW 5 to 10 knots becoming light and variable late this
evening.  27

&&

.MARINE...Broad surface ridging will rebuild over the coastal and
offshore waters through Monday with lower pressure continuing east
of the Cascades. This will lead to an increase in onshore flow with
small craft advisory westerlies likely in the central/east strait
this evening. A somewhat stronger onshore gradient will lead to the
potential for a few hours of gales in the strait Monday evening.
Thermally induced low pressure is expected to expand northward
across the interior midweek onward. This will lead to lighter winds
across interior waters, but will likely produce small craft advisory
strength N/NW winds for portions of the coastal waters at times
Tuesday through late week as a more typical summer synoptic pattern
takes hold. 27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 3 AM PDT Monday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Monday afternoon through late Monday night for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$