textproduct: Seattle/Tacoma

SYNOPSIS

Active weather continues, with a certain increase in activity as a strong atmospheric river arrives early next week. Heavy rain, river flooding, wind and high elevation snow are in the forecast for the foreseeable future. Minor coastal flooding due to high astronomical tides will remain possible for the Salish Sea coastline into the first part of the week.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

KEY MESSAGES:

* RAIN: Following a weaker system moving through the area Sunday, a strong atmospheric river will bring several rounds of heavy precipitation to the area Monday and into Wednesday. The biggest change in the forecast is the main axis of moisture has shifted farther south into Southwest Washington, and overall QPF amounts through the 72-hour period have come down slightly. This has lowered the river forecasts a touch compared to yesterday, but the key message of widespread flooding has not changed. More details are below in HYDROLOGY.

* WIND: Breezy conditions are expected throughout the week, but the strongest winds are expected on Monday, on the onset of the atmospheric river event. Wind gusts of up to 30-45 mph are in the forecast across the area, though the strongest winds are expected along the coast, in southwest Washington, and through the Cascades.

* COASTAL FLOODING: Minor coastal flooding is expected through portions of the interior waters, mostly to the north. Compound flooding from high river flows by mid-next week may prolong or exacerbate the threat of coastal flooding.

Continued moist, onshore flow is maintaining scattered showers across much of the region, except the central Puget Sound area where the showers are getting shadowed. Snow levels continue to remain just above pass level, allowing for rain at Snoqualmie Pass and a rain/snow mix at the higher passes where temperatures sit just a degree or two above freezing. Showers should taper off this evening for a bit of break until the next system arrives across the area early Sunday. The precipitation falling on Sunday will be generally not impactful; amounts of up to a quarter to a half of inch of rain through the interior, with up to an inch or two in the mountains. These rains however, will allow rivers to rise up a bit once again, and prime the soils for what will arrive next week. Showers again may taper off Sunday night but there will not be much of a break in the precipitation.

The first push from the atmospheric river arrives to the area early Monday. Rain will continue through much of the day before beginning to sink southward Monday night.

LONG TERM /TUESDAY THROUGH SATURDAY/

By Tuesday, most of the rain will be focused south of the area, which may allow the northern half of the state to see a brief break in at least the heaviest rain rates. However, another big push of precipitation will move in late Tuesday into Wednesday. This is the portion of the system that has shifted a bit farther south. Models have also begun to come more into consensus that another (albeit less impactful) system is forecast to arrive Thursday night into Friday. What happens with this system (will it be more progressive or will it stall out again over the area?) is still unclear with more significant differences in the forecast Friday and beyond.

In the main atmospheric river (72 hours from Monday - Wednesday), amounts remain track with around 2-4" of rain through the lowlands and along the coast, as well as 4 to 8 to locally 10+" of rain over the mountains, with the heaviest precipitation amounts across the southern half of the CWA. The key message has not changed: widespread river flooding, as well as urban and small stream flooding, remains a significant risk across the entire area. See more below.

Temperatures will remain above average through the week, with highs in the low to mid 50s and lows in the 40s.

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AVIATION

Active weather continues across the region as widespread showers and low ceilings in place tonight. Expect mostly MVFR to IFR ceilings to fill in across much of the interior overnight. Surface winds will continue to ease tonight, but a few gusts around 20 kt will continue around the southern portions of the area south of KBFI through around 08z. The next frontal system approaches to bring steadier rain (widespread MVFR to IFR ceilings and reduced visibility) and gusty southerly winds to 25 kt during the late morning and afternoon hours.

KSEA...MVFR ceilings this evening with trend toward IFR likely Sunday morning with rain as the next system approaches and the air mass remains saturated. Gusty southerly winds with gusts to 20 kt easing after 08z tonight, but increasing again to 20-25 kt late Sunday morning through the day.

MARINE

Onshore flow will continue to ease across the area waters tonight and waves currently between 12-15 ft will subside for a brief break in between weather systems. Another frontal system will move across the area waters on Sunday, bringing another round of increasing southerly winds to the waters. At this time, winds generally look to remain between 20-30 kt for most of the coastal and interior waters. Winds will peak during the afternoon hours again before subsiding. A stronger weather system will then move into the waters Monday, likely bringing gales to portions of the area waters. Additional weather systems will move across the area mid to late next week.

Seas over the coastal waters will slowly subside to 9 to 11 feet by late tonight. Though, expect seas to build back towards 14-16 ft on Monday and remain elevated into midweek.

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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 Sunday 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 Sunday night 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 10 PM PST this evening for Grays Harbor Bar.

Small Craft Advisory until 4 PM PST Sunday 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 to 4 PM PST Sunday 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.