420
FXUS66 KSEW 110340
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
840 PM PDT Fri May 10 2024

.SYNOPSIS...Upper level ridging across the Pacific Northwest will
lead to continued warm and dry conditions through the weekend,
though surface high pressure will peak in intensity today. A weak
system will move across southern British Columbia Sunday into
Monday. High pressure looks to build back across the region on
Monday and Tuesday with unsettled weather likely making a return
into the middle to end of next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...Overall forecast remains on
track, with no updates needed this evening. The previous discussion
follows below. 14

Clear skies with not a cloud in sight this afternoon thanks to
broad high pressure anchored across the Pacific Northwest. No
significant changes to the forecast high temperatures today and
tomorrow, though increased downslope-favored areas given morning
trends and NBM probabilistic guidance. Wouldn`t be surprised to
see a few locations top out in the upper 80s, with a 90% chance
for high temperatures of at least 90F across eastern Grays Harbor
and southwestern Mason County. Low temperatures tonight look to
drop into the low to mid 50s across the interior lowlands. While
unseasonably warm, this keeps HeatRisk values mostly in the
Yellow/Minor to Orange/Moderate level, which means affects are
more confined to individuals sensitive to heat, including those
without effective cooling and/or adequate hydration. There may be
some impacts in some health systems and in heat-sensitive
industries.

Clear skies across most of the area, aside from some scattered
clouds along the coast, which will provide for good viewing
conditions for the potential Aurora Borealis tonight. Refer to
spaceweather.gov for more space weather information.

High pressure begins shifting to our south and east Saturday,
weakening cross-Cascade gradients and weakening the thermal trough
along the coast. This leads to slightly cooler temperatures across
the region, particularly along the coast and western Olympic
Peninsula, though highs will still reach into the low 80s further
inland. A few more high clouds Saturday as well, though mostly
sunny conditions across western Washington.

The ridge further flattens and shifts to our south Sunday into
Monday as a weak shortwave and surface disturbance move across
British Columbia, bringing in slight to chance PoPs for the
northern and central Cascades. Snow levels remain well above
pass-level from 6000 to 8000 feet. Highs in the low to mid 70s
Sunday and low to mid 60s on Monday as a cold front shifts
southward across the region in association with this system.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Confidence in the extended
period from Wednesday onward remains low with the GFS and
Canadian maintaining stronger upper-level ridging both in the
deterministic and most of GEFS and GEPS runs. On the other hand,
the EC and EPS ensemble members, along with some of the GEPS
members currently favor a cooler and wetter pattern, which can be
seen in the long range ensemble cluster analysis. A handful of
GEFS and GEPS members keep the Seattle area dry through the
entire week. For now, stuck with the NBM deterministic run for
temperatures and PoP/Wx with highs near normal Wednesday, rising
slightly above normal into the low to mid 70s by the end of the
week.

Davis

&&

.AVIATION...Light winds aloft turning west as an upper-level ridge
begins to deamplify over western Washington. VFR conditions with
mostly clear skies through the TAF period. A few thin high cirrus
clouds will pass through the northern parts of the region. There is
the potential for a marine push along the coast, with low ceilings
and low visibility possible for HQM. Surface winds light northerly
to northeasterly 4 to 8 kt. Winds decrease to light and variable
tonight, becoming northwesterly 4 to 8 kt tomorrow.

KSEA...VFR with mostly clear skies, a few high clouds. NNE winds 4
to 8 kt before diminishing to light and variable (though
predominately northerly) this evening. Northwesterly winds 4 to 8 kt
tomorrow.

LH

&&

.MARINE...Broad high pressure over the northeast Pacific Ocean.
Closer to home, a weakening thermal trough remains in place along
the coast. The thermal trough will weaken throughout the day today,
with north/northeasterly flow turning northwesterly tomorrow. Winds
will begin to increase down the Strait of Juan de Fuca Saturday
night, but will remain below any thresholds (up to 15 kt). High
pressure well offshore will begin to build in closer to the region
Sunday and into the beginning, and westerly winds will increase
through the Strait of Juan de Fuca. A Gale Watch is in effect
beginning Sunday afternoon with winds increasing to 20 to 30 kt,
with gusts up to 35 kt possible (about 50% probability). High
pressure will remain over the Pacific through the forecast, but
model solutions differ with whether a frontal system will move
through the region mid-week, leaving the forecast Wednesday and
beyond highly uncertain.

Seas 6 to 8 ft through this weekend and through the beginning of
next week. Waves could approach 10 ft at times early next week as
frontal systems approach the region from the north as the strength
of these fronts is currently uncertain.

LH

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Sunday morning through Monday morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$