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 has been underway and is expected to continue through much of 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 through the the remainder of the week.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

A strong atmospheric system is well underway across the Pacific Northwest. The axis of moisture has shifted to the south this afternoon with most areas northward of Chehalis seeing drier conditions, which has provided a brief lull in rainfall across the region. However, flooding is still expected despite a brief decrease in rainfall. Heavy precipitation will fill back in later this afternoon into the early hours of the evening as the atmospheric river shifts northward and takes direct aim once again at western Washington.

This second wave of precipitation will have a longer duration of rain, with latest guidance trending a little bit wetter than previous forecasts. This longer duration rainfall will keep rivers elevated, with another round of rises on area rivers - potentially even peaking higher than the previous round. Significant river flooding is expected to continue over the next several days. The following key messages with this atmospheric river system are outlined below:

* HEAVY RAIN: Despite a decrease in rainfall this afternoon, the atmospheric river system will bring another wave of heavy rain to western Washington by this evening, continuing through Wednesday night. While areas east of the Olympics will likely see some shadowing at the onset of precipitation once again this afternoon, heavy rain will continue to cause flooding concerns to area rivers, urban areas, and areas with poor drainage. Forecast models remain consistent with rainfall forecasts, showing an additional 2 to 3 inches of rain across the lowlands and 5 to 8 inches over the mountains through late Wednesday. Many area rivers have entered major flood stage, with another wave of rises expected tonight into Thursday. For more details, see the HYDROLOGY section below.

* WINDS: Another wave of breezy winds can be expected alongside the second wave of rainfall. Wind gusts are expected to reach 40-45 mph across the region late this evening as the second wave of the atmospheric river system pushes into the region. Winds will remain breezy through 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.

In addition, snow levels are generally near 3500-4000 feet over the mountains, which has resulted in minor accumulating snow this afternoon generally above 4500 feet. Snow levels will begin to rise rapidly by this evening to 7000 to 9000 feet as the atmospheric river shifts northward.

The returning surge of moisture later this evening will bring warmer temperatures and higher snow levels throughout the remainder of the week. Temperatures will peak well above normal most days this week, with temperatures in the low to upper 50s across the lowlands.

LONG TERM /FRIDAY THROUGH TUESDAY/

Forecast models remain in good agreement that unsettled conditions will continue through the remainder of the week and into early next week as additional systems are set to cross over the Pacific Northwest. It is likely that impacts from significant river flooding will linger through Thursday and even into the weekend for many areas. Latest ensemble data have shown potentially more systems on the way through the early part of next week, starting on Monday, which will keep the pattern wet and active.

15/Mazurkiewicz

AVIATION

Deteriorating conditions are underway as the next wave of moisture begins pushing into the region. Ceilings will trend towards MVFR through the night with reduced visibilities due to moderate to heavy rain (down to as little as 2 SM). Ceilings approach IFR/LIFR Wednesday 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 tonight through Wednesday, with sustained winds at 15-20 kt gusting to 30-35 kt (possibly up to 40 kt along the coast), then diminishing late Wednesday. 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 evening will persist overnight with periods of reduced visibilities during periods of heavy precipitation. The heavier rain rates are expected around the terminal, so will likely see lesser impacts to visibilities compared to alternates. Ceilings will trend down to IFR Wednesday morning and persist through much of the day. Winds remain out of the southwest at around 5-10 kt through the evening, increasing around 08z to 15-20 kt with gusts to 25 to 30 kt through the night, with gusts increasing further to 30 to 40 kt through Wednesday afternoon, before decreasing again.

MNF

MARINE

The second frontal system with an atmospheric river will arrive later this evening and persist into Wednesday. Moderate to heavy rain over the waters (along with lower ceilings and mist) may reduce visibilities at times. South winds will begin to increase tonight, and persist into much of Wednesday. 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. The inner coastal waters and west/central Strait of Juan de Fuca were upgraded to gale warnings with frequent gusts to 35 kt likely this evening. Puget Sound waters is the next area being monitored for a possible upgrade to a gale warning (but confidence was not high enough to issue it this afternoon). Winds will decrease below any concern Thursday through early next week, where another system may produce gusty small craft winds for the coastal waters, and interior waters.

Seas of 8-12 ft will continue through Thursday, decreasing to 6 to 8 ft Sunday, increasing to 10-13 ft early next week.

HPR

HYDROLOGY

A strong atmospheric atmospheric will continue to shift back north through the Pacific Northwest tonight 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-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-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.