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FXUS66 KSEW 130326

AFDSEW



Area Forecast Discussion

National Weather Service Seattle WA

826 PM PDT Sun May 12 2024



.SYNOPSIS...Upper level ridge will continue to exit to the east

today. A weak upper level trough moves through on Monday. Another

upper level ridge will build in from the west on Tuesday and

remain in place through the remainder of the week. An upper level

trough may develop and move through late week into the weekend.



&&



.SHORT TERM /TONIGHT THROUGH THURSDAY/...Cloud coverage will 

continue to increase tonight as a weak shortwave impulse passes 

over western Washington into tomorrow. This, along with surface 

high pressure over the eastern Pacific pushing closer to the coast

will allow for a westerly push of the marine layer on Monday 

along the coast and develop mostly cloudy conditions through the 

interior. A few light showers are possible in the Cascades and 

foothills as well as the potential for a convergence zone over 

Snohomish/northern King County. High temperatures will be again be

around 10 degrees cooler than today, into the upper 50s to 60s, a

few degrees below normal for most.



Surface high pressure broadens on Tuesday and into Wednesday as 

an upper level ridge develops and approaches the region from the 

west. High temperatures will bounce back into the 70s with dry

conditions and mostly clear skies, with the exception of the 

marine layer along the coast.



.LONG TERM /FRIDAY THROUGH MONDAY/...Model guidance is still

somewhat dissonant with a 10 to 15 degree range in high

temperatures between the 25th and 75th percentile Thursday and

beyond but the synoptic pattern is beginning to look more

consistent for the long term forecast. Expecting mostly dry

conditions on Thursday. An upper level trough will move through

British Columbia and into southern Alberta, and some ensemble

members are hinting that the associated surface frontal system may

produce some showers in the Cascades on Thursday and into Friday.

Elsewhere, conditions will be mostly dry. Another upper-level

trough may approach the region next weekend, but deterministic

models disagree on the exact evolution and many ensemble members

keep conditions dry through the weekend.



LH



&&



.AVIATION...Westerly flow aloft will back to southwesterly 

tonight as an upper ridge gives way to a weak upper trough and 

associated front that will cross the region late tonight into early 

Monday. Increasing onshore low-level flow will bring a push of IFR 

to low MVFR stratus to the coast this evening. Meanwhile, expect 

ceilings to gradually lower into the MVFR range early Monday morning 

with gradual lifting to VFR possible later in the day.



KSEA...VFR with increasing high level moisture and cloud cover 

expected through the evening. Ceilings expected to fall to the 

low end of MVFR by 12Z-15Z Monday. Increasing N/NE surface winds 

to 10-13 kt as a weak shortwave approaches. Confidence on wind 

direction becomes lower after 09z, with the most likely scenario 

being a return to southerly winds. However, if the onshore push 

through the Strait of Juan de Fuca is stronger, this could create 

a more variable wind direction or delay this switch.



Cullen/Lindeman



&&



.MARINE...Onshore flow continues as a weak system approaches 

the area across the north. Elevated winds through the Strait of 

Juan de Fuca through the early morning Monday. The gale warning remains 

in effect, with small craft advisories for the adjacent waters. 

Another round of gusty winds is possible Monday night as well with 

the following disturbance so will see how winds develop with this 

round and consider any needed extensions or subsequent warnings or 

advisories.



Meanwhile, seas remain rather steep across the coastal waters this 

after noon. This, coupled with continued gusts into the 20-25 kt 

range, warrants the continued advisory through this evening. Expect 

that the winds over the coastal waters will ease and the dominant 

period to lengthen a bit, so this advisory will run through 11 PM as 

planned for now.



Onshore winds look to temporarily weaken around midweek, but again 

likely strengthen later in the week. Seas over the coastal waters

will build a bit with each passing system to 7 to 9 feet with 

periods remaining short (around 8 seconds).



Cullen



&&



.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...Small Craft Advisory until 4 AM PDT Monday for Admiralty Inlet-

     West Entrance U.S. Waters Strait Of Juan De Fuca.



     Gale Warning until 4 AM PDT Monday for Central U.S. Waters 

     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of 

     Juan De Fuca.



     Small Craft Advisory until 3 AM PDT Monday for Northern Inland 

     Waters Including The San Juan Islands.



     Small Craft Advisory until 11 PM PDT this evening 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.



&&



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