782
FXUS66 KSEW 101017
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
317 AM PDT Fri May 10 2024

.SYNOPSIS...Upper level ridge over Western Washington today with
low level offshore flow. The ridge will weaken Saturday with the
low level flow turning onshore. Ridge moving south Sunday with a
weak system moving through the area late Sunday into Monday. Ridge
rebuilding Tuesday. Unsettled weather possible for the middle of
next week.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...Satellite imagery shows clear
skies over Western Washington early this morning. Wide variety of
temperatures with locations with exposure to easterly winds in the
mid and upper 50s while locations with calm winds are in the mid
40s to lower 50s.

Warming trend continuing today with an upper level ridge over the
area. Surface gradients offshore but not very strongly with the
cross cascade gradient near 0. Temperatures aloft warming today
with 850 mb temperatures in the plus 14 to 16C range by late this
afternoon. Winds at 850 and 700 mb light easterly all day. High
temperatures warming 5 to 10 degrees in most locations putting
highs in the 70s to mid 80s inland and upper 70s to mid 80s along
the coast. Northerlies picking up over the Puget Sound this
afternoon will knock a couple of degrees off the highs near water.

Subtle changes in the pattern tonight. Offshore gradients weaken
with cross cascade gradient going positive overnight. The
weakening easterlies overnight will give the area more uniform low
temperatures, in the lower to mid 50s.

Saturday remaining warm for the interior. The question is how
warm? Is it a fake out day, winds turn onshore but not early
enough and highs are a little warmer than the day before, or the
the onshore flow get inland enough to bring a round of slight
cooling to the interior. Going with the latter this morning. In
addition to the low level flow turning onshore Saturday the ridge
aloft weakens ( 850 mb temperatures cool a couple of degrees to
the plus 12 to 14C range ) and the winds at 850 and 700 mb are
westerly from the get go. Still going to be a warm day with highs
over the interior in the lower 70s to lower 80s. With onshore flow
all day the coast will be much cooler, highs in the 60s.

Upper level ridge continues to weaken Saturday night into Sunday
with a weak shortwave approaching the area by late Sunday
afternoon. Low level onshore flow increasing Saturday night into
Sunday. Stratus along the coast Saturday night moving inland
Sunday morning stopping just short of the Puget Sound. After lows
in the mid 40s to lower 50s highs Sunday much cooler over the
interior with 60s and lower 70s. Highs along the coast only in the
lower 60s.

.LONG TERM /MONDAY THROUGH THURSDAY/...Weak shortwave moving
through Sunday night into Monday. Shower chances with this feature
confined mostly to the mountains. Under mostly cloudy skies high
temperatures will cool back to a little below normal, in the upper
50s to mid 60s.

Upper level ridge rebuilding Tuesday. Onshore gradients becoming
northerly in the afternoon. With more sunshine highs warming into
the 60s and lower 70s.

Confidence beyond Tuesday very low. Model blend has chance pops
over the area beginning Tuesday night and continuing through
Thursday. The operational GFS builds an upper level ridge over
the area Wednesday and Thursday. The ECMWF also has a ridge for
Wednesday with the ridge breaking down Thursday as a front
approaches from the northwest. Ensembles in good agreement with
the operational runs Tuesday night and Wednesday with only a
couple of the ensemble solutions wet. The GFS ensembles remain
completely dry Thursday while the ECMWF ensembles are split
between wet and dry solutions. Took the chance pops out of the
Tuesday night forecast. Will leave the blend slight chance pops in
for Wednesday and Thursday for now. If the signal from the
ensembles is as strong as tonight look for the pops to get taken
out of the Wednesday forecast. The inconsistency with the pops
extends to the temperatures as well. Both Wednesday and Thursday
the likely high temperature ranges are over 20 degrees for
Seattle. Given the ensemble solutions will lean the high
temperatures a little above normal instead of going with just
climatology with 60s and lower 70s Wednesday and Thursday. Felton

&&

.AVIATION...Offshore flow will continue aloft and down to the
surface Friday for western Washington as a high over the Pacific
peaks in intensity Friday. It will weaken going into the weekend.
For Friday, another day of mostly clear/VFR skies with potential for
a couple brief patchy fog/mist areas this morning (though the chance
is low - would affect Snohomish and Chehalis River Valleys). Surface
winds will peak this afternoon at 4 to 8 kt (with gusts to 15 kt
possible near waterways), becoming light and variable tonight.

KSEA...Continuation of clear skies expected this forecast period
with a few high clouds. North winds 4 to 8 kt with a couple gusts to
15 kt possible this afternoon, before diminishing this evening.

HPR

&&

.MARINE...High pressure/thermal trough over the Pacific waters/coast
will shift inland today/Saturday. As it breaks down, offshore flow
on Friday will revert to onshore flow Saturday. Winds for Friday
remain light with a mix of offshore/northerly winds. Couple gusts to
15 kt are possible in the Strait of Juan de Fuca/Puget Sound/Outer
Coastal Waters. A trough to the north in Canada will send a push
down the coastal waters and Strait of Juan de Fuca. With gales
possible in the Central/East Strait, a gale watch was issued from
Saturday afternoon through first part of Monday. Expect the onshore
pattern to continue into 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.

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...Gale Watch from Saturday afternoon through Monday morning for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

&&

$$