978
FXUS66 KSEW 151624
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
924 AM PDT Thu Aug 15 2024

.SYNOPSIS...Weak troughing over the region will maintain cooler
and partly cloudy conditions through the rest of the week. A low
will deepen along the coast through the weekend, increasing the
threat of thunderstorms across western Washington on Saturday and
Sunday. Unsettled conditions will persist into next week with a
continuation of cooler temperatures and chances of showers.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...No significant changes made
to the forecast this morning. The previous discussion can be found
below along with updated aviation and marine discussions:

A weak low pressure system will continue to push inland across
Oregon and lift northeastward throughout the day today,
maintaining cloudy conditions and below normal temperatures in the
mid 60s to mid 70s across western Washington. A wave of lofted
smoke will be advected northward into the region, but is expected
to stay above the surface, resulting in little more than hazy
skies. As the low exits the state, wrap around moisture will
generate isolated showers over the Cascades later this afternoon
and evening. While confidence is low, a lightning strike or two
cannot be ruled out on the western side of the Cascade crest.

The weakening low will move northward into British Columbia by
Friday, maintaining a chance of showers and isolated thunderstorms
over the North Cascades. Elsewhere, weak onshore flow will
maintain cloudy skies and cooler temperatures with highs across
the lowlands peaking once again in the low to mid 70s.

A low pressure system will deepen off the Pacific Northwest coast
on Saturday, which will bring the next round of weather to western
Washington. Moisture will surge inland Saturday afternoon and
evening, generating widespread showers and thunderstorm activity
that will linger into early Sunday. Instability will increase as a
frontal system lifts northward across the state later on Saturday,
with probabilistic guidance showing a 15% to 30% chance of
thunderstorm activity into the evening hours. Nocturnal thunder
also cannot be ruled out with favorable dynamics in place. Latest
ensemble guidance suggests roughly half an inch of rainfall across
western Washington over the weekend, though this will be highly
dependent on where showers set up and where any heavier showers
and thunderstorms develop. While forecast models continue to hone
in on thunderstorm potential for the weekend, ensembles still
show some uncertainty of the track of the upper level low, which
could lead to differences in rainfall totals, timing, and
thunderstorm chances. As for now, the threat for storms continues
to be monitored as new guidance becomes available.

.LONG TERM /MONDAY THROUGH WEDNESDAY/...Forecast models continue
to favor troughing into next week, maintaining cooler temperatures
and chances for lighter shower activity across the region.
Temperatures are on track to stay several degrees below normal
through the period, giving us a preview of early fall-like
conditions.

Lindeman

&&

.AVIATION...High pressure will weaken over the area today with
troughing developing over the area tonight for light flow aloft.
Stratus along the coast has moved into southern Puget Sound this
morning with generally MVFR/IFR in these areas. VFR mid clouds also
exists over a portion of central Puget Sound. Cigs will improve to
VFR SCT/BKN this afternoon and evening. Onshore flow will increase
again this evening with stratus developing along the coast tonight
and moving into southern Puget Sound again Friday morning for areas
of MVFR/IFR cigs.  W/SW winds continue through today.

KSEA...VFR cigs this morning with a BKN/OVC mid-level deck. Brief
periods of FEW/SCT 010-015 clouds possible through 18z, but expected
to remain mainly VFR. VFR this afternoon and evening. Stratus may
near the terminal from the SW on Friday morning, with approximately
a 35% chance of MVFR cigs from 12-18z. Light west winds this morning
will increase from the SW this afternoon. JD

&&

.MARINE...A weak cold front will move through the region early this
morning. While remaining dry across the region Thursday, areas of
low stratus and patchy fog have been observed in the coastal waters,
and onshore flow will push some of the stratus through the Strait of
Juan de Fuca this morning, covering portions of Puget Sound,
Admiralty Inlet, and the Northern Inland Waters. The low stratus/fog
may reduce outward visibilities at times through Thursday afternoon.

Gusty winds up to 25 kt are expected with this push through the
Strait of Juan de Fuca today, which will be hazardous for small
craft (thus an advisory was issued Thursday afternoon through Friday
morning for Central & East Strait of Juan de Fuca). Winds over the
coastal waters will remain light and turn northwesterly Thursday
afternoon into the weekend. Winds will also be light during this
time out of the south in all inner waterways (with west winds in the
Strait of Juan de Fuca). There is a slight chance for thunderstorms
Saturday afternoon through Sunday morning for inner waters as a
strong upper level low moves in. Threat for gusty sustained winds
remains low with this system (except for possible gusts from
thunderstorms).

Seas will generally remain 3 to 5 feet through next week.

HPR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Friday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$