151
FXUS66 KSEW 122144
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
244 PM PDT Thu Sep 12 2024

.SYNOPSIS...Weak upper level ridging will allow for drier
conditions today before another upper level trough enters the
region on Friday. Wet, cooler, and unsettled conditions will
continue through the weekend. Next week will start with brief
drying ahead of another wet system, maintaining below-normal
temperatures through the period.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Cloudy skies with isolated
shower activity south and east of the Puget Sound will persist
today under northwest flow aloft. Onshore flow will cause cloudy
skies to stick around, with periodic sun breaks in the afternoon.
High temperatures today will stay on the cool side but will
increase a degree or two from yesterday, peaking in the mid to
upper 60s for much of the lowlands.

Flow will flatten overnight into Friday as weak ridging passes
over the region. The next system will move into the Pacific
Northwest later in the day, with a front and associated showers
moving onto the coast by the late afternoon. Showers will
overspread western Washington by late Friday evening with a
surface front sliding across the area Saturday afternoon. The bulk
of the moisture will be focused over the North Cascades, where
weak instability will allow for locally heavier showers and may
produce a few lightning strikes. Convergence zone showers are
also favored to develop Saturday evening over and east of the
Puget Sound while activity decreases elsewhere. Temperatures will
remain below normal through the short-term in the mid 60s for most
low elevations.

.LONG TERM /MONDAY THROUGH THURSDAY/...An upper level trough will
dive south of the region on Sunday, maintaining cooler
temperatures and generating more scattered shower activity across
western Washington. Split flow will develop overhead by Monday as
ridging amplifies from the west, allowing conditions to briefly
dry out and warm up a few degrees. Uncertainty increases heading
into next week, though ensembles continue to highlight another
storm system moving into the region on Tuesday with another,
potentially heavier, round of precipitation across western
Washington. Cooler temperatures will also persist, remaining
several degrees below normal for mid-September.

Lindeman

&&

.AVIATION...Northwesterly flow aloft will persist tonight with an
upper level ridge over the region. Flow aloft will become more
westerly through the day on Friday as the ridge flattens and a
trough sinks down into the region from the north. Onshore flow
will continue in the low levels through the period. Conditions
across the area terminals are primarily VFR to MVFR this afternoon
with latest satellite still showing stratus across much of western
Washington. Expect ceilings to continue to lift towards 3000-4500
ft heading into this evening. Ceilings look to lower again area-
wide into Friday morning, with most terminals likely becoming
MVFR. Ceilings then look to lift and scatter again between 18-20Z
Friday.

KSEA...Ceilings have lifted back to VFR this afternoon. Expect
this trend to continue through the evening hours. Redevelopment of
low stratus is expected Friday morning, with probabilistic
guidance showing a 45-50 percent chance of MVFR conditions
developing at the terminal near 12Z. Winds are W/SW at 4-8 kts and
will become light again overnight. 14

&&

.MARINE...Surface high pressure will continue to build into the
coastal waters tonight, with onshore flow expected to persist
over the next several days. Westerly winds along the Strait of
Juan de Fuca will increase to 10-20 kt this evening. While
conditions remain rather marginal, latest hi-res guidance still
indicates roughly a 50-60 percent probability of frequent gusts to
25 kt into early Friday. Thus, have issued a Small Craft Advisory
for the central and eastern Strait. Winds will diminish again
through early Friday morning.

A weak system will sink southward and move into British Columbia
Friday into the weekend. This will push a weak cold front through
the area waters Friday night into Saturday. Increased onshore flow
will persist in its wake, so may see another round of gusty
westerly winds along the Strait Saturday night into Sunday. High
pressure then looks to build back into the coastal waters early
next week, before another system moves into the area waters on
Tuesday.

Seas are generally hovering between 4-7 ft this afternoon and will
continue to subside towards 3-5 ft again by the weekend. Seas then
look to build back towards 5-8 ft again across the outer coastal
waters by early next week. 14

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon 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.

&&

$$