textproduct: Seattle/Tacoma

SYNOPSIS

The first showers of the frontal system have arrived along the coast and will continue to spread inland throughout the day. Expect rain, breezy winds, heightened marine activity and a slight chance of a thunderstorm today. Showery and unstable conditions linger into Tuesday before high pressure returns later in the week.

SHORT TERM /TODAY THROUGH WEDNESDAY/

A rainy Memorial Day is in store for today, as well as breezy winds and a slight chance for thunderstorms. As for forecast changes, areas from Island County north will be a little bit more shadowed, receiving a few hundredths of an inch of rain. Areas from Seattle south will receive up to a quarter of an inch. Locally higher amounts are possible in any thunderstorms that develop. Favored locations for thunderstorms, though still a slight chance (10-15%) include the Olympic Peninsula down through the Chehalis Valley. Winds will be strongest along the coast with gusts of 35 to 40 mph, with breezy conditions through the north interior as well. Temperatures will be much cooler today, struggling to get much above the upper 50s to low 60s.

Conditions will remain showery and unstable on Tuesday as the low pressure system continues to move through the Northwest. The areas favoring thunderstorms have been trimmed back to include areas from Chehalis south into far southwestern Washington. Isolated chances for thunderstorms cannot be ruled out on Wednesday for all of western Washington.

Unseasonably large waves will arrive at the coast late today, peaking on Tuesday between 14-16 feet with long periods bringing high surf conditions to the Pacific coast. Waves will decrease throughout the day on Tuesday.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

By midweek, the region is in split flow transitioning to gentle ridging into mid-week. Temperatures begin to warm again from Wednesday onward, getting back into the 70s by Thursday. Guidance is suggestive of another period of troughing over the northwest late in the week with showers lingering in the forecast. As of now, it looks to only be enough to produce mountain showers and thunderstorms into the weekend.

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AVIATION

Increasing southwest flow aloft today will transition to southerly tonight as a frontal system moves across Western Washington. High clouds continue to increase early this morning with lower stratus along the coast. MVFR/IFR cigs along the coast this morning as rain moves onshore. The front will move into the interior sites around midday through the afternoon with increasing rain. Cigs will lower into MVFR or low-end VFR this afternoon for Puget Sound terminals. Cigs will then continue to fluctuate between VFR/MVFR into Monday evening for most sites, with MVFR along the coast. There remains a low probability (less than 10%) for a thunderstorm along the Olympic Peninsula this afternoon into the evening. In addition, vsbys may briefly drop towards 3-5 SM during steadier rain, particularly along the coast. Increasing south winds this morning will peak during the day. Gusts will range 20 to 30 kts along the coast and from Everett northwards, with wind gusts 20 to 25 kt elsewhere.

KSEA...VFR cigs early this morning with increasing high clouds. Rain expected to move into the terminal around 17-19z as a frontal system moves across the area. Cigs will slowly lower towards low-end VFR by early afternoon. Probability for MVFR cigs remains highest (around 30-35%) this afternoon, mainly between 21 to 01z following the onset of the rain. Otherwise, VFR cigs expected into tonight, lowering towards MVFR into Tuesday morning. South-southwest winds increasing around 18z with gusts ranging 20 to 25 kts through 00z. South winds continue but slowly ease into tonight. JD

MARINE

A low pressure system will move into the waters today as a cold front moves through the area. Southerly winds continue to increase early this morning. South winds will peak for the Coastal Waters through mid-morning, with winds peaking for the interior waters during the day. Widespread Small Craft Advisory winds for most waters with the cold front, with gale force gusts over the northern Coastal Waters. Brief gale force wind gusts may also be observed over the eastern Strait of Juan de Fuca and northern inland waters, with localized gusts around 35 kts. Otherwise, SCA wind gusts peaking around 25 kts for Puget Sound this afternoon.

Winds will then slowly subside tonight into early Tuesday. High pressure then quickly rebuilds on Tuesday with winds transitioning more north to northwesterly Tuesday afternoon. SCA northwest wind gusts are then expected at times from Tuesday through much of the week for the outer Coastal Waters. Onshore flow will also increase Thursday through late week, with increasing west winds through the Strait of Juan de Fuca each evening. SCA winds are expected late Thursday and again late Friday for the Strait, with potentially gale force winds during this period as well.

Seas of 7 to 10 feet this morning will build further to 12 to 17 feet late today into Tuesday. Seas will slowly decrease on Tuesday, dropping to around 10 feet by Wednesday. Steep seas will also return late Tuesday into Wednesday for the outer Coastal Waters with increasing northwest winds and a period decreasing to around 10 seconds. A long period swell of 7 to 10 feet with a period of 15 seconds will also arrive on Thursday. This will result in the significant wave height rising above 10 feet, before seas slowly ease on Friday. JD

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...High Surf Advisory from 5 PM this afternoon to noon PDT Tuesday for Grays Harbor County Coast-Northern Washington Coast.

PZ...Small Craft Advisory from 11 AM this morning to 11 AM PDT Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Grays Harbor Bar.

Small Craft Advisory until 5 AM PDT Tuesday for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 PM PDT this afternoon for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.

Gale Warning until 11 AM PDT this morning for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm.

Small Craft Advisory until 11 AM PDT Tuesday for 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.