textproduct: Seattle/Tacoma

SYNOPSIS

River flooding continues across areas of western Washington. Drier conditions will persist through tonight, before a weak front crosses the region early Sunday. A stronger system will follow Monday into Tuesday, bringing heavier precipitation and strong winds for some areas. A deeper trough will bring cooler air and the potential for heavy mountain snow Tuesday night into Wednesday. Conditions remain unsettled heading into late week with additional rounds of lowland rain and mountain snow expected.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

Most areas of fog have scattered across the region this afternoon with latest satellite imagery showing high cloud cover streaming in overhead. Conditions will generally remain dry across the region through tonight with high pressure situated over the region.

The break in the weather will remain short-lived, however, as the ridge flattens into Sunday and the next weak frontal system approaches western Washington. Rain will move inland by early Sunday, but expect overall amounts to remain rather light, with most areas only expected to receive a few hundredths to a tenth of an inch across the interior and a few tenths along the coast. Snow levels will remain rather high- generally between 6000-8000 ft - so rainfall amounts in the mountains are generally expected to range from a quarter of an inch to an inch in spots, but are not expected to bring additional impacts at this time.

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LONG TERM /MONDAY THROUGH SATURDAY/

Models remain consistent with regards to next atmospheric river system getting into full swing early Monday morning and bringing another round of significant rainfall throughout the day. QPF amounts with this particular system are lower than with the prior AR with lowland rainfall amounts generally in the half- inch to three- quarters of an inch. The problem arises when considering the impacts this new rainfall may have on already existing conditions from prior AR. Needless to say, flooding due to already elevated river levels and landslides due to already saturated ground top that list. However, this is both not as bad as it appears to be and just as bad as it appears to be. To cover the first part of that statement, precip amounts favor falling mostly in the first half of the day, tapering off in the afternoon and evening...even though PoPs throughout the day remain high. Making the situation as bad as it appears, or perhaps worse, is the follow-up frontal system Tuesday, drawing in a much more significant slug of moisture into the area. This will result in lowland rainfall amounts of 0.75 inches on the low end and as high as 1.50 inches on the high end. The cumulative effects of Monday and Tuesday will certainly compound already existing issues over the area. Lastly, winds during the day on Monday will be elevated with most locations in the CWA becoming breezy to locally windy. Locations more prone to higher wind speeds, especially along the coast, the San Juans and the NW interior may see winds approach wind advisory criteria, but that risk will need to be evaluated once this system enters the near term time frame.

Switching gears to higher elevations, snow levels remain high Monday before starting to lower Monday night and into Tuesday. With the aforementioned incoming moisture for Tuesday, accumulating snowfall will be an issue as snow levels by Tuesday night will dip down to pass level. Winter weather headlines may be needed if guidance remains consistent.

Wednesday brings a weak ridge, but unfortunately is not strong enough scour all of the moisture out of the area. As such, this will keep at least showers in the forecast...even though, thankfully, QPF values remain low during this time. A broad upper level trough over the northwestern Canadian coast will keep weather over W WA active for the remainder of the forecast period, continuing to cycle moisture into the area and keeping the latter end of the forecast wet.

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AVIATION

Southwesterly flow aloft as an upper ridge axis gradually shifts to the east. Winds will remain light near the surface at all terminals this afternoon. With fog having dissipated, terminals have mostly rebounded to VFR this afternoon.

A front will approach from the west after 02Z and bring elevated winds between 10-15kts at KPAE and KHQM. The front is expected to reach all other terminals between 07-11Z. Winds at the remaining terminals will generally be less than 8kts with the front. Rain and associated MVFR flight conditions/ceilings are expected along and behind the front. Rain is forecast to end at most terminals by 16Z with lingering reduced flight conditions possible after rain ends.

KSEA...VFR conditions through tonight. A front will begin to approach the terminal around 11Z. Light rain will accompany the front with the greatest chance of MVFR flight conditions between 14Z-16Z Sunday. Winds remain from the south to southeast and around or less then 6kts the entire TAF period.

MARINE

A weak frontal system will cross the waters later today through early Sunday, generating SCA winds and seas above 10 feet across the far northern coastal waters. Seas will remain between 6 to 9 feet elsewhere.

A stronger system will arrive late Sunday night into Monday, which will bring stronger winds to the outer waters that will likely reach Gale force. This system will also bring larger swells to the region, with waves reaching 15 to 20 feet early next week.

Seas will remain elevated throughout the rest of next week as another series of systems crosses the area waters. There will likely be another round of wind and sea headlines, with winds potentially reaching Gale force across most area waters mid week.

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HYDROLOGY

Rivers continue to recede this afternoon as western Washington gets a break from the wet weather. Even the lower reaches of the rivers will approach or lower below flood stage later today into tonight. The exceptions to this will be the lower reaches of the Chehalis river which will not fall below flood stage until Sunday from Porter down to Grays Harbor, and the lower reaches of the Skagit river which will recede to near flood stage by Monday morning.

Rivers will be on the rise again later Monday into Tuesday with another atmospheric river taking aim at Western Washington. Rainfall amounts to 3 to 5 inches Monday through Wednesday in the mountains are forecast. Another round of river flooding will occur with the atmospheric river but at this time, with the Skagit and Snohomish Rivers forecast to reach major flooding once again by midweek. A Flood Watch has been issued for much of western Washington Monday morning through Thursday evening for potential incoming river flooding, urban flooding, and small stream flooding.

With very wet antecedent soil conditions, the landslide threat remains high across the region. Potential is also elevated for debris flows over area burn scars, which continue to be monitored.

The threat of urban flooding will increase again later Monday into Tuesday. Small stream flooding, as well as areas with poor drainage, will pose a risk of localized nuisance flooding and ponding on roadways later Monday into Wednesday.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Flood Watch from Monday morning through Thursday 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-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-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 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.

Gale Warning from 10 PM Sunday to 4 PM PST Monday 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.