textproduct: Seattle/Tacoma

SYNOPSIS

A strong atmospheric system will continue to bring periods of heavy rain and gusty winds to western Washington through Wednesday. Widespread significant river flooding is underway and will continue through the week. Minor coastal flooding due to astronomical high tides will also pose concerns for the northern Salish Sea coastlines through much of the week. Wet and unsettled conditions will continue into early next week.

SHORT TERM /TODAY THROUGH FRIDAY/

A strong atmospheric river system is well underway across the Pacific Northwest, with heavy rain pushing into western Washington this morning. Forecast models have increased precipitation amounts with this round of incoming moisture, leading to even higher river forecasts and potential for more widespread major flooding to occur. Widespread precipitation is slated to continue region-wide through Thursday morning, with lingering showers through Friday. This long duration of precipitation will cause significant rises to area rivers, which are already running very high. Significant river flooding is expected to continue through the week, with potential for flooding impacts to continue into the weekend.

The following key messages with this atmospheric river system are outlined below:

* HEAVY RAIN: Widespread heavy rain will continue throughout the day today as an atmospheric river remains focused over western Washington. This will continue to cause flooding concerns to area rivers, urban areas, and areas with poor drainage. Forecast models have increased rainfall totals, with an additional 1 to 3 inches of rain across the lowlands and another 4 to 8 inches over the Olympics and Cascades through Thursday morning. Locally higher amounts are possible over higher terrain of the western Washington Cascades. A majority of area rivers have reached Moderate to Major flood stage, with some rivers forecast to break flow records. Rises to area rivers will continue with this incoming rainfall, and more details can be found in the HYDROLOGY section below.

* WINDS: Breezy winds will continue across western Washington tonight into Wednesday, with widespread gusts reaching 40 to 45 mph. Winds will remain elevated through Wednesday evening before gradually weakening into Thursday. The breezy winds, combined with deeply saturated soils, raises the risk of downed trees and localized power outages Wednesday.

* COASTAL FLOODING: Minor coastal flooding remains possible along the northern Salish Sea coastlines during Wednesdays high astronomical tide. While the tides will generally remain below or nearing thresholds, heightened river flows or wind effects could exacerbate inundation in some areas around high tide.

While temperatures through the period will be mild with highs in the low to mid 50s, snow levels will briefly lower in the North and Central Cascades to 3500-4500 feet Thursday afternoon. This will result in brief snow accumulations through the higher passes from Stevens Pass northward.

High pressure will build over the western US on Friday, amplifying northward into the Pacific Northwest. While additional systems will continue to bring precipitation into the region, it will shift northward on Friday. This will allow shower activity to weaken, with light rainfall amounts lingering mainly over higher terrain and generally north of the Puget Sound. While some areas will see drier conditions, area rivers may remain elevated with flooding concerns continuing.

LONG TERM /FRIDAY NIGHT THROUGH MONDAY/

Ensembles have keyed in on high pressure continuing to build northward on Saturday, potentially bringing some relief to continued wet conditions across western Washington. This will be short lived, with the next weather system on track to cross the Pacific Northwest on Sunday, with another potentially very wet system on its heels. It is likely that flooding impacts will linger into the weekend, and conditions will continue to be closely monitored.

15

AVIATION

Deteriorating conditions are underway as the next wave of moisture continues to push into the region. Ceilings will continue to trend towards IFR/LIFR this morning and visibilities down to 1-3 SM with mist. This looks to last much of Wednesday and into Thursday with marginal improvements. Expect winds to pick up out of the southwest throughout the day today, with sustained winds at 15-20 kt gusting to 30-35 kt (possibly up to 40 kt along the coast), then weakening late this evening. The strongest winds will be in the southern/central terminals. Some low-speed wind shear can't be ruled out with the initial onset of winds, but is primarily expected to be more of a low-level turbulence issue (with winds aloft staying out of the southwest below 2,000 ft).

KSEA...MVFR ceilings this morning will continue to trend down towards IFR with periods of reduced visibilities during periods of heavy precipitation. IFR conditions are favored to persist through much of the day as periods of heavy precipitation continue. Winds remain out of the southwest at around 15-20 kt with gusts to 25 to 30 kt this morning, with gusts increasing further to 30 to 40 kt through the afternoon, before decreasing again into Thursday morning.

MNF

MARINE

An atmospheric river system will continue to bring active conditions to the Pacific Northwest through Thursday morning. Moderate to heavy rain over the waters, along with lower ceilings and areas of fog, may reduce visibilities at times. Elevated southerly winds will persist into much of Wednesday across all area waters. West winds will follow in the Strait of Juan de Fuca late Wednesday evening. Most waters are under small craft advisories for the breezy winds, with gales through the Strait of Juan de Fuca and along the inner coastal waters. Puget Sound waters is the next area being monitored for a possible upgrade to a gale warning. Winds will decrease below thresholds Thursday through early next week, before another system may produce gusty small craft winds for the coastal waters and interior waters on Sunday.

Seas of 10 to 15 ft will continue through Thursday, subsiding to 6 to 8 ft by Friday and remaining through the weekend. Seas will increase once again to 10 to 13 ft early next week.

HYDROLOGY

A strong atmospheric atmospheric will continue to shift back north through the Pacific Northwest this morning through late Wednesday. This will bring another round of significant heavy rainfall across the area. 48-hour precipitation amounts ending Wednesday night will likely reach 2 to 4 inches across the lowlands, with 6 to 10 inches over the Olympics and Cascades with locally higher amounts over 12 inches in the the central and southern Cascades.

Most rivers across western Washington will be affected by this second wave and many flood warnings remain in effect. Consult weather.gov/seattle for the latest. While some uncertainty does still remain in regards to the exact flood levels and stages, many river forecast points are projected to reach major flood stage in the days ahead and several may even approach or exceed the previous floods of record. Therefore, it will be critical to monitor the forecasts now and through the next seven days. Additional precipitation is also possible Thursday and Friday, which may keep rivers elevated heading into the weekend.

A Flood Watch remains in effect across all of western Washington through Friday.

With the wet antecedent soil conditions, the landslide threat across the region will increase with this system. Potential has also increased for debris flows over area burn scars, which will continue to be monitored.

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 roadways. Low water crossings may become impacted or impassable.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Flood Watch 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 7 AM to 1 PM PST Wednesday for Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-San Juan County.

Wind Advisory until 10 PM PST Wednesday for City of Seattle- Downtown Everett / Marysville Area-Eastern Kitsap County- Eastside-Foothills of the Western and Southern Olympic Peninsula-Grays Harbor County Coast-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties- Lowlands of Pierce and Southern King Counties-Middle Chehalis River Valley-Northern Washington Coast-Olympia and Southern Puget Sound-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 10 PM PST Wednesday for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca- Grays Harbor Bar-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.

Gale Warning until 10 PM PST Wednesday for Central U.S. Waters Strait Of Juan De Fuca-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 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 10 PM Wednesday to 4 AM PST Thursday for Central U.S. Waters Strait Of Juan De Fuca-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 10 PM Wednesday to 4 AM PST Friday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

Small Craft Advisory until 4 AM PST Friday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.