632
FXUS66 KSEW 091552
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
852 AM PDT Thu May 9 2024

.SYNOPSIS...Upper level ridge centered offshore nosing into
Southern British Columbia today. The ridge will remain in place
Friday then begin to weaken Saturday. Low level flow turning
offshore today. Offshore flow continuing into Friday with the
flow turning onshore Saturday. Weak upper level trough moving
through later Sunday. A weaker ridge will temporarily rebuild
Monday. Another trough will arrive late Tuesday into Wednesday.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Satellite imagery continues
to show clear skies across Western Washington, with some
dissipating low stratus across the coastal waters. Temperatures
across the area as of 830 are in the low to mid 50s, up to around
60 along the Strait of Juan de Fuca. Temperatures will continue to
warm into the 70s, with a few spots reaching into the lower 80s in
the Southwest Interior and through the Cascade valleys. Surface flow
will turn east/northeasterly through out the day with
northeasterly winds in the the low levels In short, significant
warming is expected today across the area with inland temperatures
about 10 degrees warmer than Wednesday and temperatures along the
coast 15 degrees or so warmer versus yesterday.

Little change in the pattern overnight into Friday. Temperatures
aloft continue to warm with 850 mb temperatures in the plus 13 to
plus 15C range by late Friday afternoon. Lows tonight in the upper
40s to mid 50s, close to record high minimum temperatures in some
locations. Highs Friday a little warmer with 70s to mid 80s.
While not expecting record highs Friday, temperatures this warm
are unusual for the first half of May. Seattle has only had 3 days
in the 80s on May 10th in 79 years of records.

Even with the surface temperatures warming quickly waters around
Western Washington are still very cool. Water temperatures this
morning, Lake Washington 54 degrees, Lake Sammamish 56 degrees and
Puget Sound in the lower 50s. The rivers are even colder with the
Cedar River at 48 degrees, the Skykomish and Tolt 46 degrees and
the Skagit checking in with a cold 45 degrees. Cold water shock
can be deadly. If you are going to be on the water wear a life
jacket.

Upper level ridge weakening Friday night into Saturday. Low level
offshore flow turning weak onshore. Winds at 850 and 700 mb turn
west northwesterly. With the ridge weakening slightly
temperatures aloft cool a touch with model 850 mb temperatures
late Saturday afternoon plus 12 or 13C. Another night of mild low
temperatures, close to record high minimums in places, in the
lower to mid 50s. Highs Saturday much cooler along the coast, in
the mid 60s with highs over the interior in the 70s and lower 80s.

Felton/LH

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Models in good agreement
Sunday with the ridge continuing to weaken and an upper level
trough riding over the ridge into British Columbia late in the
day. This feature doesn`t have much punch with just a chance of
showers in the Olympics and Cascades north of about Snoqualmie
Pass Sunday night. Ensembles are weaker with the upper level
trough versus the operational runs. Operational runs have highs
only in the 60s for the interior Sunday. Will lean a little
towards the ensembles and go for highs in the 60s and lower 70s.

Upper level ridge tries to rebuild Monday but the ridge axis is
well offshore and low level onshore flow continues through the day.
Temperatures aloft continue to cool. This combination will lower
high temperatures Monday back into the 60s.

Model solutions become inconsistent Tuesday and Wednesday with
the ECMWF building a stronger ridge over the area while the GFS
has a front approaching from the northwest Wednesday. High
temperature spreads by Wednesday rather large. For Seattle 80
percent of the solutions have the high between 78 and 58 degrees.
With the large amount of uncertainty will split the difference and
have highs in the 60s and introduce a slight chance of showers
Tuesday night and Wednesday.

Felton

&&

.AVIATION...Northeasterly winds aloft today with a ridge building
off the Pacific coast and moving into the area. Clear skies today
into tonight other than a few high clouds at times. Northerly winds
will increase midday and remain breezy for some areas, generally 6
to 12 kts with occasional gusts to 20 kts, with winds slowly
subsiding this evening.

KSEA...VFR/clear skies expected during the period. North winds 8 to
12 kts with gusts near 20 kts possible through this afternoon, winds
transitioning more NE at 5 to 8 kts tonight.

JD

&&

.MARINE...High pressure has built up some over the waters, and
building will continue over the State of Washington today. With a
thermal trough underneath the ridge up the coast, flow is
predominately offshore with north/northeast winds. Winds for
Thursday may gust up to 20 kt in the coastal waters, as well as
Puget Sound and Central Strait of Juan de Fuca (but are expected to
remain below hazardous levels for small craft). This pattern will
continue into the weekend, until a trough moves through the region
Saturday/Sunday. Gusty winds above 20 kt are possible in the Strait
of Juan de Fuca and the outer coastal waters - will continue to
monitor for possible headlines.

Seas of 5 to 8 feet through late week into next week.

HPR

&&

.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.
&&

$$