222
FXUS66 KSEW 092120
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
220 PM PDT Thu May 9 2024

.SYNOPSIS...An upper level ridge will continue to build over the
region today and Friday with warm and clear conditions. The ridge
will begin to break down Saturday. A weak upper level trough will
move through Sunday night into Monday. Ridging looks to rebuild
offshore into the middle of next week with an trough moving south
from the Gulf of Alaska towards the region late Tuesday into
Wednesday.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Clear skies and
temperatures warming into the low 70s early this afternoon as an
upper-level ridge and surface thermal trough along the coast
dominate the weather pattern for the next few days.

High temperatures today should reach the mid to upper 70s, with a
few spots hitting close to 80, including the Southwest Interior
and the Cascade valleys. Tonight with clear conditions should
allow for efficient cooling and keep low temperatures into the
low to mid 50s through the interior, though this will approach
record maximum low temperatures across the area. Weak downslope
flow over the mountains will keep the valleys and west-side
foothills much warmer, in the mid to upper 50s to 60s.

Friday looks to be the warmest day for most, with temperatures
reaching into the low 80s, perhaps the mid to upper 80s through
the west-side foothills and valleys of the Cascades and Olympics.
Some high clouds may build in through the northern portions of the
region. Low temperatures again in the low to mid 50s.

On Saturday the ridge will begin break down as the jet stream
begins to move southward. Highs will be much cooler along the
Pacific Coast, in the 60s along the immediate shoreline up to the
70s farther inland. Through the interior, highs similar if not a
touch warmer, to the upper 70s to low 80s. Low temperatures in
the upper 40s to low 50s.

Clouds will begin to increase in coverage Sunday as a weak upper
level trough will dig and quickly move through the region late
Sunday into Monday. A few light scattered showers may be possible,
especially in the higher terrain, but generally expect to remain
dry. High temperatures remain slightly above average, in the low
to mid 70s, though cooler along the coast in the 60s.

Water temperatures remain cold across the region, with Lake
Washington at 53, Lake Sammamish at 56, ocean temperatures in the
upper 40s, and river temperatures ranging from the mid 40s to low
50s. Cold water shock can be fatal, even with air temperatures in
the 80s. Dress accordingly for cold water and wear a life jacket.

.LONG TERM /MONDAY THROUGH THURSDAY/...Models are in good
agreement that a ridge will develop again just offshore over the
eastern Pacific Ocean with a trough developing over the Gulf of
Alaska and moving through British Columbia Wednesday into Thursday.
Models diverge on how far south the cold front from this system
will develop and thus determine the chance for some potential rain
showers, with the ECWMF 12Z deterministic and ensemble runs most
optimistic for widespread rain, while the GFS and CMC 12Z runs
show lesser chances for rain and the front much farther north. The
current forecast reflects a slight chance of showers and high
temperatures a touch below normal, in the upper 60s. Starting
Wednesday, NBM shows a large spread in the high temperature
forecast with a 15 degree spread between the 25th and 75th
percentiles. NBM also shows a large spread in the precipitation
forecast.

LH

&&

.AVIATION...Northeasterly winds aloft will transition more light
tonight into early Friday with an upper ridge over the area. Clear
skies this afternoon. Clear skies will continue into Friday with
just a few high clouds at times. Brief, patchy fog can`t be ruled
out, mainly towards Whatcom County and Snohomish and Chehalis River
Valleys, but confidence is low. Northerly winds into this evening
will taper off tonight, before increasing Friday afternoon.

KSEA...Clear skies expected during the period with a few high
clouds. North winds 8 to 14 kts into this evening will lighten to 5
to 8 kts tonight.

JD

&&

.MARINE...High pressure will continue over the waters and across the
area into the weekend. A thermal trough will exist along the coast
for predominately northerly and periods of offshore flow. Winds
expected to remain generally below Small Craft Advisory threshold
through Friday, although brief wind gusts near 20 kt may occur over
Puget Sound and inner Coastal Waters. Northwest winds will increase
over the Coastal Waters Saturday. Stronger west winds expected for
the Strait of Juan de Fuca Saturday night and then again later
Sunday with increasing onshore flow. Otherwise, an onshore flow
pattern returns early next week.

Seas will generally range 5 to 7 feet into Saturday, briefly
building to 8 to 9 feet for the outer Coastal Waters over the
Saturday into Sunday.

JD

&&

.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...None.
&&

$$