textproduct: Seattle/Tacoma

SYNOPSIS

Active weather continues through the week, with a potent atmospheric river still on track to impact western Washington Monday into Wednesday. Additional systems are forecast for late in the week. Minor coastal flooding due to high astronomical tides will remain possible for the Salish Sea coastlines into the first part of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

KEY MESSAGES:

* RAIN: A weather system has arrived early this morning and will produce rain throughout the day. QPF amounts will be around 1-2 inches in the Cascades, and a quarter to half inch in the lowlands. A strong atmospheric river will arrive on Monday, producing an extended period of heavy rain through Wednesday. The forecast has remained on track from the previous change of having a greater focus on QPF shifted slightly south. From areas generally of Seattle south, 2.5 to 5 inches of rain is still favored. The Olympics and Cascades are on track to receive 6-10 inches, with locally higher amounts receiving nearly 12 inches of rain through late Wednesday night.

* WIND: Monday will be windy, particularly in areas south of Seattle. Southwesterly wind will pick up Monday morning and remain elevated into the overnight period. Expect gusts of 35 to 40 mph, tapering off into late Monday night.

* COASTAL FLOODING: Minor coastal flooding remains possible as the high astronomical tide cycle has shifted more so to the Salish Sea into Monday. While the tides will generally be below or just close to thresholds, affects from heightened river flows or wind effects on Monday could exacerbate the inundation around high tide.

The rain from the atmospheric river will persist throughout the day on Monday, sinking slightly southward into the evening. The moisture axis will lift north and pulse back up again Tuesday into Wednesday. There will be a number of area rivers reaching moderate to major flood stage, more of which can be found in the hydrology section.

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LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

The ongoing, strong atmospheric river will impact Tuesday, with the model indications showing that the moisture plume will pulse back to the north again, but not enough to keep the heavier rain rates going in the northern sections of the CWA. By around midday on Wednesday, the hose like precipitation will be tapering off more significantly as the atmospheric river loses steam. That said, don't expect a full break in the precipitation. Additional systems bringing rain are forecast for later in the week. There are some ensemble differences in whether the ridge will rebuild and force some of the precipitation to the north, or keep the pattern fairly progressive.

This will be a significant week of rainfall. The overarching message has not changed in that there will be widespread river flooding and likely more urban and small stream flooding as well.

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AVIATION

West-southwest flow aloft will continue through today as a frontal system moves across Western Washington. Widespread MVFR cigs early this morning with areas of IFR cigs as well. Rain continues to spread northwards ahead of the next weather system, with steady, stratiform rain through this morning. Post-frontal showers are expected this afternoon. MVFR/IFR cigs into this afternoon, with some localized improvements to VFR generally after 00z, particularly in central and northern Puget Sound. Otherwise, MVFR/IFR cigs expected tonight into Monday morning. Vsbys may briefly lower to 2-5 statute miles this morning during the steadier precipitation. S/SW surface winds through the TAF period will increase this morning, with gusts peaking between 20 to 25 kts in the afternoon.

KSEA... MVFR cigs early this morning. Predominantly MVFR cigs expected into the afternoon. Cigs may lower into IFR late morning, mainly between 17 to 21z, with current probabilities of IFR cigs around 30%. BKN MVFR cigs mainly 22z onwards in a post-frontal airmass, with brief periods of low-end VFR possible in the evening. MVFR cigs then expected late tonight into Monday. Steadier rain this morning, will taper to showers after 19-20z. Brief vsby reductions to 3 to 5 statute miles this morning during the rain. South winds of 5 to 10 kts this morning will transition more SW between 19 to 20z and increase, with gusts this afternoon ranging 20 to 25 kts. JD

MARINE

A weather system will move across the waters today, with increasing south to southwest winds. Small Craft Advisory winds are expected for the majority of waters this afternoon. SCA winds will mainly be driven by gusts, with wind gusts peaking between 20 to 30 kts during this period. Winds will briefly subside this evening into tonight. A stronger weather system will then move into the waters on Monday, with winds peaking Monday afternoon into Monday evening. A Gale Warning has been issued for the Coastal Waters due to the high confidence of gale force wind gusts on Monday. Gale Watches have also been issued for Puget Sound and northern inland waters on Monday, with the probability of gales ranging 60 to 90 percent, with the highest probabilities along portions of Puget Sound. In addition, a westerly push is expected late Monday into Monday night for the Strait of Juan de Fuca, and additional headlines will be necessary. Winds will briefly subside on Tuesday, with another weather system Tuesday night into Wednesday bringing increased winds.

Seas will range 7 to 9 feet into tonight, before building to 13 to 16 feet on Monday. Seas will remain elevated above 10 feet through midweek. JD

HYDROLOGY

A series of wet weather systems moving across the region will increase the threat of river flooding early next week. While there's still some uncertainty in the precipitation amounts with an atmospheric river moving into the region, confidence continues to increase that a widespread river flooding event will commence late Monday and continue through much of the week. Multiple rivers flowing off the Cascades and the Olympics are forecast to reach Minor, Moderate, and Major flood stage. While uncertainty does remain in regards to the exact flood levels and stages through the next week, it will be critical to monitor the forecasts through the next seven days. Additional precipitation is also possible Thursday into Friday, which will keep rivers elevated through the second half of the week.

The series of wet systems will also start to elevate the landslide risk across the region. As soils become more saturated next week, there will be an increased potential for landslides and debris flows on burn scars.

Urban and small stream flooding, as well as areas with poor drainage, should be alert to the potential for localized nuisance flooding. Low water crossings may become impacted or impassable.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Coastal Flood Advisory from 5 AM to 11 AM PST this morning for Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-San Juan County.

Coastal Flood Advisory from 6 AM to noon PST Monday for Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-San Juan County.

Flood Watch from late tonight through Friday afternoon for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County-Cascades of Whatcom and Skagit Counties-City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Eastern Strait of Juan de Fuca-Eastside- Foothills and Valleys of Central King County-Foothills and Valleys of Pierce and Southern King Counties- Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Grays Harbor County Coast-Island County-Lake Crescent Area Including US 101-Lower Chehalis River Valley- Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Middle Chehalis River Valley- Northern Hood Canal-Northern Washington Coast-Olympia and Southern Puget Sound-Olympics-Port Townsend Area-San Juan County-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Western Strait of Juan de Fuca-Willapa and Black Hills.

PZ...Small Craft Advisory until 4 PM PST 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.

Small Craft Advisory from 7 AM this morning to 4 PM PST 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 Watch from Monday morning through Monday 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.