FXUS66 KSEW 190312
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
812 PM PDT Thu Jul 18 2024

.SYNOPSIS...Dry and warm conditions will continue across western
Washington into the weekend with high pressure building aloft. An
upper level trough moving into British Columbia early next week
will cool temperatures closer to seasonal norms and increase night
and morning cloudiness.

&&

.UPDATE...Skies remain clear this evening with temperatures still
in the 70s to 80 inland. A marine push will likely bring in cloud
cover for Friday morning before clearing out late morning. Please
see discussion below for more details of the forecast (as well as
a refreshed aviation section).

HPR

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Satellite imagery shows
stratus has dissipated across the interior and mainly retreated
back to the coast this afternoon. High temperatures today look to
generally top out in the 70s to low 80s for the interior and 60s
along the coast.

A weak upper trough will swing through the coastal waters on
Friday, but currently does not look to impact the forecast too
much at this time. It will, however, promote onshore flow and will
help push another round of stratus into the interior overnight
into Friday morning. Stratus looks to dissipate by midday Friday
with high pressure building into the region aloft. Temperatures
on Friday look to top out in the upper 70s to mid 80s across the
interior and in the upper 60s to low 70s along the coast.

Upper ridging will then amplify over the weekend, with 500mb
heights building into the low to mid 590s dam. With onshore flow
weakening and 850 mb temperatures near 20C, expect surface
temperatures to warm into the 80s to low 90s. Areas most likely to
approach 90 will be from Seattle southward and in the Cascade
foothills and valleys. Areas along the coast look to top out in
the 70s.

The upper level ridge will weaken somewhat on Sunday as onshore
flow increases and another upper level shortwave approaches the
coast. Temperatures will cool a few degrees along the coast, and
generally look to top out in the 60s and low 70s. Temperatures
across the interior, however, look to remain fairly warm, topping
out in the mid to upper 80s.

.LONG TERM /MONDAY THROUGH THURSDAY/...Ensemble guidance remains
in good agreement with an upper level trough moving into British
Columbia early next week. This will help promote onshore flow,
cooler temperatures, and more evening and morning cloudiness
across western Washington. There could be some drizzle near the
coast or a few light showers in the North Cascades at times, but
overall precipitation chances look rather low for now. Temperatures
generally look to trend closer to seasonal norms, in the 70s to
low 80s across the interior and 60s to low 70s along the coast. 14

&&

.AVIATION...Flow south-southwest aloft as an upper-trough is
positioned offshore. In the lower levels, high pressure centered
offshore with onshore flow. VFR across all TAF sites as marine
stratus has all but burned off. However, stratus will rebound
tonight into Friday morning. Confidence isn't high in regards to a
deep marine layer intrusion but MVFR/IFR cigs are possible from the
coast, strait, and near Puget Sound. Any lingering stratus should
give way to clear skies by 18-20z Friday.

KSEA...Mostly clear skies through tonight. NBM has a 30-35% chance
of MVFR marine stratus arriving at the terminal around 12-14z
Friday. If it makes it, cigs should burn off by 18z. Southwesterly
winds around 4-8 kt for much of the upcoming period.

McMillian

&&

.MARINE...High pressure over the offshore waters through next week.
Onshore flow will prevail in varying degrees into next week as well.
As a result, SCA through the central and eastern strait will be in
the cards as one is currently in effect this evening through early
Friday morning. Additional headlines may be needed again Sunday and
and Monday evening for these marine waters.

McMillian

&&

.FIRE WEATHER...We'll see a return of warmer and dry conditions
through the end of the week, with afternoon minimum RHs again
dipping closer to critical thresholds by Friday through Sunday in
the Cascades. At this point, there's not an overwhelming signal for
significantly increased winds, but instability may increase enough
to keep a mention of elevated concern. Another disturbance may again
bring some renewed threat for thunderstorms late Sunday across some
portion of the mountains, but confidence isn't particularly high for
now. Finally, expect a somewhat cooler and more humid pattern to
emerge into early next week as the pattern switches to be dominated
by an upper level trough over the region. Cullen

&&

.CLIMATE...With two weeks left to go in July Seattle-Tacoma
airport has received zero rain this month. Not even a trace. It is
pretty rare for July to not of gotten any rain at all by this
point of the month. It has only happened 4 times in 80 years of
records, this year, 2023, 2017 and 1985. The record dry month of July
for Seattle is a trace in 2021, 2017, 2013, 1960 and 1958. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Friday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$