117
FXUS66 KSEW 132206
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
306 PM PDT Tue Aug 13 2024

.SYNOPSIS...Mostly cloudy and cooler than normal, with isolated
showers and possibly thunderstorms in the North Cascades near the
crest this afternoon and evening. Morning clouds, with afternoon
sunshine and near normal temperatures Wednesday and Thursday.
The pattern looks to trend wetter into the weekend with what
amounts to a good chance of widespread precipitation for much of
the region.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Cool and cloudy weather
continues today with an upper level troughing over the region.
There remains a chance of isolated showers and around a 15%
probability of thunderstorms along the crest of the North
Cascades. The thicker stratus layer over the area has been making
it pretty tough for sunbreaks this afternoon, while it is possible
that few locations may see a little sun late this afternoon - most
locations are likely to remain cloudy through the evening.

The weak upper level trough exits east on Wednesday, allowing
heights will build through the day. Morning clouds are expected to
scatter out for many locations in the early afternoon as onshore
flow eases. More sunshine will help afternoon temps rise to near
normal levels - into the mid to upper 70s in the interior and mid
to high 60s along the coast. Thursday will see pretty similar
conditions - morning clouds with afternoon clearing and near
normal temperatures. A weak upper level trough moving to the
south may help boost showers again over the higher terrain - with
a 15 to 20% chance of thunderstorms along the crest of the
Cascades Thursday afternoon and evening.

Friday looks to be a transitional day as a system approaches the
area from the northwest. This will likely result in a bit more
marine stratus Friday morning with a later break out for many
areas, except the coast which will likely remain mostly cloudy.
Temperatures will remain just below normal and there is another
chance of showers over the mountains as well as isolated
Thunderstorms.

.LONG TERM /SATURDAY THROUGH TUESDAY/...The grand ensemble -
including the EPS, GEFS and GEPS systems has been consistently
showing the offshore upper level low lingering over the NE Pacific
through much of the weekend. The overall effect will be cooler and
more significantly, wetter conditions through the weekend. There
are very good chances of widespread prectipitation affecting the
area. By Sunday afternoon there is a 75% of at least widespread
light rain over all of Western Washingtion, with lower
probabilities for heavier amounts particularly over the higher
terrain. In addition there is some chance of thunderstorms in the
area as well. At the very least this does look like the most
widespread rain for the region in some time.

&&

AVIATION...Light, variable flow aloft will continue into tonight
with an upper trough moving east of the area. Widespread VFR cigs
continue this afternoon with areas of MVFR lingering, primarily
along the coast. VFR will continue into early tonight for the
interior with LIFR/IFR cigs developing along the coast. Cigs will
likely lower towards MVFR for portions of Puget Sound Wednesday
morning, with clearing expected by late morning. Lower vsbys
expected along the coast. W/SW winds will continue for most into
this evening before becoming light tonight.

KSEA...VFR cigs with mid-level clouds. VFR continue into early
tonight. Cigs are expected to lower towards MVFR, with the highest
probabilities of MVFR (around 30%) between 12-18z. Southwest winds
between 6 to 10 kts this afternoon are expected to transition more
N/NW tonight, before becoming SW Wednesday morning. JD

&&

.MARINE...Onshore flow will continue for the majority of this week
across the area waters. Diurnally driven pushes are expected through
the Strait of Juan de Fuca each evening. The best potential, over
the next few days, of SCA winds through the Strait of Juan de Fuca
is Thursday evening. Otherwise, lower visibilities may be possible
tonight along the inner Coastal Waters as well as the Strait of Juan
de Fuca. Seas will remain 2 to 4 feet through Thursday and briefly
build to 5 to 6 feet along the outer Coastal Waters on Friday. JD

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$