textproduct: Seattle/Tacoma

SYNOPSIS

A strong atmospheric river will impact the area Monday through Wednesday, bringing periods of moderate to heavy rainfall and the threat for significant river flooding to the area. Gusty winds also move through the area Monday. Minor coastal flooding due to high astronomical tides will remain possible for the Salish Sea coastlines through the first part of the week. Wet and unsettled conditions will continue through the end of the week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Showers continue across the area this afternoon in the wake of a frontal system that moved through the area this morning. Expect shower activity to continue into tonight.

Conditions then become wetter on Monday with a strong atmospheric river still on track to move into the region and impact the area through Wednesday. The key messages regarding this system are highlighted below:

KEY MESSAGES:

* RAIN: A strong atmospheric river will arrive on Monday, bringing extended periods of moderate to heavy rain to western Washington through Wednesday. The most significant change within the last 24 hours has been the shift in the axis of moisture with this system. At this time, the moisture plume still looks to shift south briefly on Tuesday, however the latest guidance has it lifting back northward into the area Tuesday night into Wednesday. This has resulted in an increase in precipitation totals across the central and south Cascades this afternoon. While this will have an impact to river forecasts, the overall message is that it will be a wet first half of the week for the region. Areas generally south of Seattle are still expected to see around 2.5 to 5 inches of rain in a 72 hour period. The Olympics and Cascades are on track to receive 6-10 inches of rain, though locally higher amounts across the central and south Cascades of close to 12 inches will be possible through late Wednesday night.

* WIND: Monday will be windy across the region area-wide. Southwesterly winds will pick up Monday morning, peak Monday evening, and gradually ease Monday night into Tuesday. The strongest winds are expected along the coast, but expect gusts to 40-45 mph at times across the interior. Gusts to 50-55 mph will be possible along the immediate Pacific coast.

* COASTAL FLOODING: Minor coastal flooding remains possible for the Salish Sea coastlines through the first half of the week with high astronomical tides. While the tides will generally remain below or just close to thresholds, heightened river flows or wind effects could exacerbate inundation in some spots around high tide.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Unsettled conditions look to continue across the second half of the week, though precipitation gradually looks to taper across the area through the day Thursday. Ensemble guidance does hint at the building of a ridge along the West Coast Friday into the weekend, which would help push the storm track further to the north. This may be short-lived however, as there is some indication that the ridge axis will shift further inland over the weekend and open the door for additional, weaker systems to make their way into western Washington.

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AVIATION

Mix of lower MVFR to IFR ceilings across most terminals this evening, though conditions remain variable in a moist, stable air mass across the region. Some scattered showers linger overnight, but expect continued varied ceilings. More impactful conditions arrive Monday morning with heavy rain, lower ceilings, and gusty southerly winds developing across the area late morning through the day Monday. Ceilings will lower through the day down to MVFR/IFR as the rain progresses through the region, and expect IFR visibility in heavy rain at times. Strong southerly winds during the afternoon and evening with bring gusts to 40 kt across much of the region.

KSEA...Ceilings likely fluctuate a bit this evening with abundant low level moisture maintaining some periods of IFR ceilings though some wind may keep things patchy at times this evening. Meanwhile, gusty winds to 20 kt continue this evening, easing by 09z. Expect steadier rain to arrive after 16z Monday with low ceilings, gusty winds to 30 kt and IFR visibility at times through the day. Winds likely peak late afternoon with gusts to 40 kt but remaining elevated through early Tuesday.

MARINE

A brief lull in the winds is expected across the region tonight as the area remains in between weather systems. A stronger weather system will then move into the waters on Monday, with winds expected to peak Monday afternoon and evening. Gusts to gale are likely for the majority of the area waters on Monday, with latest probabilities still showing roughly a 60 to 90 percent chance of winds reaching 35 kt for much of the area (especially along the Sound). A push is expected down the Strait of Juan de Fuca late Monday into Monday night, where a round of westerly gales looks likely. Winds will subside across the area waters heading into Tuesday. Additional systems moving into the area throughout the week may bring elevated winds and seas to the area waters at times.

Seas between 6 to 8 feet tonight will build to 13 to 16 feet on Monday. Seas will remain elevated above 10 feet through midweek, before subsiding to 7 to 9 ft on Thursday.

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HYDROLOGY

A strong atmospheric atmospheric will move through the Pacific Northwest Monday through Wednesday, bringing significant heavy rainfall across the area. While there's still some uncertainty in the precipitation amounts with an atmospheric river moving into the region, confidence remains high 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 now and through the next seven days. Additional precipitation is also possible Thursday into Friday, which may keep rivers elevated through the second half of the week.

With the wet antecedent soil conditions, the landslide risk across the region will increase with this system. There may also be potential impacts to the area burn scars as well.

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

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Flood Watch from 4 AM PST Monday 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.

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.

Wind Advisory from 7 AM to 10 PM PST Monday for City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-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- Island County-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-Northern Hood Canal-Olympia and Southern Puget Sound-Port Townsend Area- San Juan County-Shoreline / Lynnwood / South Everett Area- Southern Hood Canal-Willapa and Black Hills.

Wind Advisory from 4 AM to 10 PM PST Monday for Eastern Strait of Juan de Fuca-Foothills of the Western and Southern Olympic Peninsula-Grays Harbor County Coast-Lake Crescent Area Including US 101-Lower Chehalis River Valley-Middle Chehalis River Valley-Northern Washington Coast-Western Strait of Juan de Fuca.

PZ...Small Craft Advisory from 10 AM Monday to 4 AM PST Tuesday for Grays Harbor Bar.

Gale Warning from 10 AM to 10 PM PST Monday 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-West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 1 PM to 10 PM PST Monday for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 4 AM to 10 AM PST Monday 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 from 7 AM to 7 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.