170
FXUS66 KSEW 201649
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
949 AM PDT Sat Jul 20 2024


.UPDATE...We`re on track to seeing the warmest day for the
foreseeable future here today. Current temperatures are several
degrees warmer than the previous day`s around this time. Highs are
forecast to top out over 10 degrees above average for interior
locations. No changes made to the inherited forecast as the
previous discussion remains below.

&&


.SYNOPSIS...Dry and warm conditions will continue across western
Washington through the weekend with an upper level ridge
continuing to amplify over the region today. A weak shortwave may
bring very spotty showers to the coast and mountains on Sunday.
An upper level trough moving into British Columbia early next week
will cool temperatures closer to seasonal norms and increase
night and morning cloudiness.


&&

.SHORT TERM /TODAY THROUGH MONDAY/...Recent satellite imagery
shows stratus along the immediate coast, attempting to push
through the interior.. with not much luck. Stratus will be quick
to burn back this morning, allowing for another warm and dry day. Upper
level ridging will continue to amplify over western Washington
through this afternoon with southerly flow aloft. This will allow
temperatures to warm throughout the interior into the upper 80s
and possibly even lower 90s. Areas along the coast and water will
be in the mid 70s.

The aforementioned upper level ridge will gradually shift eastward
tonight into Sunday as a weak upper level trough offshore
approaches the area. Onshore flow looks to increase on Sunday with
a stronger stratus push in the interior, which will allow
temperatures to be slightly cooler through the day. High temps
will range from the low to mid 80s through the interior, and mid
60s for the coast.

A shortwave looks to pass over the region through Sunday and may
have enough juice to produce some very light precipitation over
the coast, although looking less likely at this time. Along with
possible light precip along the coast, thunderstorms may be
possible along the Cascade Crest particularly in the afternoon.
Latest guidance still suggests around an 10% chance of an
isolated thunderstorms in the Cascades, so will continue to
monitor this trend as it develops, with confidence remaining low.

A pattern change seems increasingly likely as we head into Monday,
with a broad upper level trough moving through our region. This
will allow for increased onshore flow and temperatures near
normal. High temps look to generally be in the mid 70s for the
interior and low 60s for the coast.

.LONG TERM /TUESDAY THROUGH FRIDAY/...The broad upper level trough
will continue to influence our weather through the long term, with
periods of onshore flow, morning stratus, and temperatures near
season normals. Temperatures look to stay in the 70s for the
interior and the 60s for coastal locations. As of right now,
there looks to be nothing in the way of any meaningful
precipitation.

Mazurkiewicz


&&

.AVIATION...A strong upper ridge axis remains east of the Cascades
with an upper trough offshore for south to southwest flow aloft
over Western Washington today. Low level onshore flow is weaker
today, however stratus has pushed down the Strait and along
portions of the immediate coast, briefly bringing conditions down
to IFR/LIFR for coastal terminals at times. Latest satellite does
show that stratus has already started to scatter and retreat back
to the Pacific this morning. Expect this trend to continue over
the next few hours for a return to VFR for all area terminals.
VFR conditions will prevail across the interior of Western
Washington through this evening. Marginally stronger onshore flow
tonight is expected to pull the marine layer further inland to
near or just west of Puget Sound by early Sunday morning.

KSEA...Clear skies. Surface winds north to northeasterly this
morning persisting at 6 knots or less. Winds will shift more to
the northwest and rise to 7 to 10 knots by mid- afternoon. 27/14

&&

.MARINE...Broad surface ridging remains centered over the offshore
waters with lower pressure across the interior. Thermally induced
lower pressure will shift eastward tonight inducing a modest
marine push with small craft advisory westerlies likely in the
central and east strait. Onshore flow increases further on
Sunday...with the potential for small craft advisory northwesterlies
across portions of the coastal waters and the potential for
westerly gales in the central/east strait. An upper level trough
moving into the region on Monday will keep moderate onshore flow
in place for a likely continuation of headlines for the strait and
coastal waters.

A series of weak upper troughs moving onshore well into the coming
week will keep varying degrees of onshore flow in place. 27


&&


.FIRE WEATHER...Warm and dry conditions into Sunday. Afternoon
minimum RHs dipping close to critical thresholds for the lowlands
and through Sunday for the Cascades. Instability may increase
enough to keep a mention of elevated concern for the Cascades
especially this afternoon and evening. Another disturbance may
bring a renewed threat for thunderstorms Sunday with southerly
flow across some portion of the mountains, with high resolution
ensembles including the NBM still supporting a 10-15% chance of
thunder. Will continue to monitor the threat for an isolated
thunderstorm or two, with upper level dynamics still not looking
as impressive. A cooler more humid pattern develops Monday as the
pattern switches to be dominated by an upper level trough over the
region.


&&


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

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

&&

$$