246
FXUS66 KSEW 302322
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
422 PM PDT Sun Jun 30 2024

.SYNOPSIS...Lingering showers ending and clouds scattering across
the region this afternoon. High pressure will build far offshore
maintaining modest onshore flow that maintains temperatures near
normal for the next few days. High pressure then shifts over the
region, bringing about a sharp warm up starting around the
Independence Day holiday and continuing through the weekend.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...A few stray showers
remain evident on radar this afternoon, but all told a rather mild
and increasingly less cloudy day across Western Washington.
Despite the improvement, some additional light showers are
possible tonight into early Monday as another weak disturbance
slides across the region. Otherwise, expect a return of low
stratus or fog to the coast tonight through early Monday morning.
A few light showers clip the area, but this will be the end of any
talk of precipitation through the balance of the week. The
offshore ridge will remain in place and gradually strengthen. With
it remaining offshore, this should maintain some onshore low-level
flow that will hold temperatures generally near seasonal normals
through Tuesday and Wednesday with some morning clouds giving way
to afternoon sunshine.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Strong agreement in the
global ensemble guidance for the ridge to begin to build eastward
over the Pacific Northwest around the Independence Day holiday,
ushering in a period of above normal temperatures. The big
question centers around how strong the ridge gets and when it
moves over the region. The most likely scenario, which remains
reflected in the forecast, brings widespread Moderate HeatRisk to
the lowlands Friday and Saturday with temperatures climbing
through the 80s and some local spots around 90 degrees. It`s worth
noting that for next weekend, the spread in potential temperatures
grows significantly, reflecting some uncertainty between various
camps of ensemble solutions. There are subsets of each ensemble
system that suggest either a weaker ridge or less persistent
ridge. As a result, the deterministic NBM temperature values,
which remain close to the 50th percentile of the distribution,
continue to be used for the forecast today. With the increased
temperature and lower relative humidities, it is expected that the
grasses and other finer fuels will have time to begin further
drying ahead of the holiday weekend. This may lead to elevated
fire weather concerns in addition to the potential heat impacts
late this week.

&&

.AVIATION...An upper level trough has moved east of the Cascades
this afternoon, with a surface low and trough situated in eastern
Washington, and another weak low off the coast. CIGs have improved
to VFR this afternoon with a mix of scattered to broken clouds with
low bases at 3,500 feet. Model guidance has a large portion of
lowland areas clearing going into the evening, with low clouds still
hanging on in the Cascades and the coastline. Shower activity has
been extremely limited, although there remains the chance for more
showers towards the Cascades (with an isolated thunderstorm). Breezy
southwest winds will continue this afternoon (gusts to 20 kt), and
will become northwest with diffluence through the Strait of Juan de
Fuca (becoming northwesterly for KPAE and KBFI and potentially KSEA).

An onshore push early Monday morning will bring widespread MVFR CIG
coverage for terminals between the Cascades and Olympics. The best
chance for IFR/LIFR ceilings (with the potential for fog) are areas
in the Cascades. All coverage of low CIGs/VIS will lift up and
scatter to VFR (except the coastline) late Monday morning. Variable
winds in the morning will become more westerly into the afternoon
(with more diffluence of the push through the Strait of Juan de Fuca
of winds spreading out to the north/south).

KSEA...VFR with CIGs continuing to scatter out throughout the
afternoon and evening. Convergence zone shower activity is expected
to be weak, but some of the north winds from KPAE and KBFI may make
their way to KSEA as early as 00Z. Winds will go light and variable
tonight. MVFR CIGs likely early Monday morning, but will scatter out
late morning/afternoon. Winds expected to pick up from the north 4
to 8 kt late morning.

HPR

&&

.MARINE...An upper level trough is exiting western Washington this
afternoon. There remains a weak surface low over the waterways, but
otherwise high pressure is expected to build over the Pacific
throughout the week, with stronger pushes of onshore flow this
afternoon and Monday. Flow will become northwesterly over the
coastal waters as the high begins to shift towards land.

Breezy west winds of 15 to 25 kt are still expected to develop in
the Central/East Strait of Juan de Fuca this evening through tonight
(small craft advisory remains in effect). For tonight and tomorrow:
low marine cloud coverage and fog is possible along the coastline.
Some of the fog may be dense. A stronger push is expected Monday
evening. Sustained winds are expected to reach 20 to 30 kt but there
may be gusts to 40 kt. The gale watch will remain in effect for now.
The northwest flow for Tuesday into Thursday over the outer coastal
waters may approach 15 to 25 kt. Seas may also increase to 8 to 10
feet at 9 seconds during this period (will be 4 to 6 feet outside of
Tuesday - Thursday period).

HPR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 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.

&&

$$