530
FXUS66 KSEW 181634
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
934 AM PDT Thu Jul 18 2024

.SYNOPSIS...High pressure aloft will maintain dry conditions
along with a gradual warming trend across Western Washington into
the coming weekend. An upper level trough moving into British
Columbia early next week is expected to cool temperatures and
increase night and morning cloudiness.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...An upper level disturbance
that brought a few thunderstorms to the Cascades last night continues
to push eastward across northern Idaho this morning. This feature
initiated a marine push yesterday evening. Satellite imagery this
morning shows that marine stratus has pushed inland into the Sound.
Stratus has already started to rapidly dissipate across the interior
and will continue to do so and retreat back to the coast through
the remainder of the morning hours. This will make way for a more
widespread sunny afternoon, with even coastal areas expected to
see a little sunshine. High temperatures will range from the 60s
along the coast to the 70s and lower 80s inland. The remainder of
the previous discussion follows below, with updates made to the
aviation and fire sections. 14

Another weak upper trough will swing across the coastal waters on
Friday. This won`t have much affect on the forecast apart from
tempering an inevitable warming trend. Upper ridging gains
amplitude on Saturday with 500 millibar heights rebounding into
the lower to mid 590s dam. With only light onshore flow and 850
millibar temperatures near or above 20C, temperatures at or above
90 F look likely for interior areas from Seattle southward on
Saturday.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The ridge weakens somewhat
on Sunday and onshore flow increases, but this should still
equate to a fairly warm day across the interior of Western
Washington. Deterministic models and ensembles still remain firm
with the idea of an upper trough moving into British Columbia
early next week. Given the time of year and depth of the trough,
the main effects for the region will be cooler temperatures and
more widespread night and morning cloudiness. There could be some
local drizzle near the coast or the odd shower in the North
Cascades, but that would be the extent of any precip as things
stand. Nonetheless, this would be our first venture into anything
temperature wise that resembles normal in almost three weeks. 27

&&

.AVIATION...Upper level ridge to the east and an upper level
trough offshore giving Western Washington southwesterly flow
aloft. In the lower levels high pressure centered offshore with
onshore flow.

Stratus covering most of the lowlands west of the Puget Sound
currently with MVFR ceilings. Weakening onshore flow has has slowed
down the eastward expansion of the stratus and lowered the chances
of the stratus getting east of Puget Sound. Stratus retreating back
to the coastline by 19z leaving clear skies for the afternoon except
right along the ocean beaches. Stratus moving inland again tonight
but with weaker onshore flow good chance it will not get east of
Puget Sound again Friday morning.

KSEA...Mostly clear skies this morning through tonight. Southerly
wind 4 to 8 knots becoming west southwesterly 21z-03z.

Felton/McMillian

&&

.MARINE...High pressure centered over the offshore waters
extending over the remainder of the waters through the first part
of next week with varying degrees of onshore flow. Westerly
pushes through the Strait of Juan de Fuca each night with small
craft advisory winds tonight and again Sunday and Monday evening.

Felton

&&

.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 from 6 PM this evening to 2 AM PDT Friday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$