000
FXUS66 KSEW 161602
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
902 AM PDT Tue Apr 16 2024

.UPDATE...No changes to the overall forecast this morning. Please
see the aviation and marine sections below for updates to those
forecasts.


&&

.PREV DISCUSSION... /issued 401 AM PDT Tue Apr 16 2024/


.SYNOPSIS...Cool upper level trough over the area today will move
east tonight. High amplitude upper level ridge building offshore
extending into Northern British Columbia tonight and Wednesday.
Weak upper level trough swinging down the backside of the ridge
moving through Thursday. Upper level ridge building over Western
Washington Friday will move east Saturday as a weakening front
moves through the area. Another ridge will build into the Pacific
Northwest Sunday into the first part of next week.

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...Satellite imagery shows
cool upper level trough over the area this morning. Doppler radar
indicating a convergence zone over Northern King county with
isolated showers over the remainder of the area. Temperatures at 4
am/11z were in the upper 30s to mid 40s.

Trough weakening as it remains over Western Washington today.
Convergence zone staying intact this morning before dissipating
this afternoon. The zone will wobble around between the northern
half of King county and the southern half of Snohomish county.
Scattered showers with the convergence zone with just isolated
shower activity outside of the zone. With the trough overhead
temperatures will remain cool with highs mostly in the lower to
mid 50s.

Trough moving east tonight with little shower activity there is
left with the trough wrapping up in the evening hours. Skies
clearing a bit with an upper level ridge building offshore. Air
mass aloft still cool and with little wind in the lower levels
good chance we will see freezing low temperatures in the Southwest
Interior, southern end of the Hood Canal and into the Lower
Chehalis Valley. Have issued a frost advisory for Wednesday
morning between 2 and 9 am. Lows in the 30s.

Upper level ridge continuing to build offshore into Northern
British Columbia with dry north northwesterly flow aloft over the
area. Temperatures warming after a cool start with highs a couple
of degrees either side of 60.

Ridge remaining in place Wednesday night. Weak and fairly dry
upper level trough moving down the backside of the ridge into
Western Washington Thursday. Low level flow turning weakly
offshore Thursday pushing high temperatures mostly into the 60s.
Lows Thursday morning in the 30s and lower 40s.

.LONG TERM /FRIDAY THROUGH MONDAY/...Extended models in good
agreement with upper level ridge rebuilding over Western
Washington Friday. Low level flow still weak offshore. Friday
looks to be the warmest day of the forecast period with highs in
the 60s and the warmer locations near 70. Ridge shifts east Friday
night into Saturday allowing a weakening front to move through
by Saturday night. Not much left of this system by the time it
reaches Western Washington so will just have chance pops Saturday
afternoon and Saturday night. Surface and upper level ridge
building behind the front Sunday. Low level flow switching to
onshore behind the front will result in cooler high temperatures
Sunday, near 60. A little warmer Monday as the ridge continues to
build and the low level flow turns offshore with highs in the
upper 50s to mid 60s. Felton

&&

.AVIATION...A few showers are lingering near KPAE keeping conditions
MVFR there, otherwise VFR across the region this morning. BKN skies
will persist throughout the day, becoming mostly clear by tonight.
Conditions look to remain VFR through the TAF period.

Winds northwesterly along the coast and through the north interior
(BLI). At Seattle, winds 6 to 10 kt will veer from SE to NW by this
afternoon, continuing to veer to light SW tonight.

.KSEA...VFR conditions with BKN to SCT skies. COnditions expected to
remain VFR through the TAF period. SE winds 6 to 10 kt veering to NW
this afternoon, then veering back to light NE to SE by tonight.
North winds 8 to 12 kt expected tomorrow.

LH

&&

.MARINE...Northwesterly winds and onshore flow will continue today
and into Wednesday as a surface high pressure ridge continues to
work its way towards the coastal waters. Winds will turn offshore on
Friday as a thermal trough develops along the coast. Relatively calm
winds expected through the rest of the week. The next frontal system
will traverse the region on Saturday.

Steep seas will continue through today with seas 6 to 8 ft at around
8 seconds, for which there is a Small Craft Advisory for the coastal
waters and the West Entrance to the Strait of Juan de Fuca. Seas
will ease tomorrow to 4 to 6 ft early tomorrow and will continue
through the end of the week.

LH

&&

HYDROLOGY...No river flooding expected in the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Frost Advisory from 2 AM to 9 AM PDT Wednesday for Hood Canal
     Area-Lower Chehalis Valley Area-Southwest Interior.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal
     Waters From Cape Flattery To James Island 10 To 60 Nm-
     Coastal Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
     To Cape Shoalwater Out 10 Nm-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$