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 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 forecast period.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

A strong atmospheric system is well underway across western Washington this morning, bringing in widespread heavy rainfall to western Washington alongside breezy winds. The axis of moisture will continue to shift southward throughout the morning today behind a cold front with most areas northward of Chehalis seeing drier conditions, providing 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 by this evening as the atmospheric river shifts northward and takes direct aim once again at western Washington. While this second wave of precipitation will not bring quite as heavy rain rates, this longer duration rainfall will keep rivers elevated across the region, and even potentially causing rivers to peak higher, with significant river flooding expected to continue over the next few days.

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

* HEAVY RAIN: Despite a decrease in rainfall this morning, 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: Winds will gradually decrease this morning, with another wave of breezy winds this afternoon alongside the second wave of rainfall. Wind gusts are expected to reach 40-45 mph across the region later today as the second wave of the atmospheric river system pushes into the region. Winds will peak this evening and remain elevated into Wednesday.

* COASTAL FLOODING: Minor coastal flooding remains possible today along the northern Salish Sea coastlines with high astronomical tides. 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 will briefly lower to near 3500-4000 feet over the mountains this morning, resulting in minor accumulating snow generally above 4500 feet. The higher mountain passes, including Stevens Pass and White Pass, will likely see a few inches of snow accumulation throughout the day today which could cause brief slippery travel conditions.

The returning surge of moisture later this afternoon will bring warmer temperatures and higher snow levels through 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 /THURSDAY THROUGH MONDAY/

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. Mild conditions are favored to continue through the forecast period, with little relief from wet conditions in sight for western Washington.

15

AVIATION

Generally MVFR to IFR as heavy rainfall from an atmospheric river slowly shifts southward this morning. This should allow for some small improvement in ceilings and vis this morning, though conditions are expected to deteriorate once again as heavy precipitation fills in across western Washington this afternoon. North to northeast winds generally 10 to 20 kt with gusts up to 25 to 30 kt will continue to ease this morning and shift southerly by 12z. Winds will increase once again this evening, with speeds returning to 10 to 20 kt with gusts reaching 30 kt.

KSEA...IFR this morning with slight improvement to MVFR this morning after 12Z. May see some brief improvement to low- end VFR conditions around 21Z, but ceilings are expected to deteriorate late Tuesday evening into the overnight hours to IFR. Southerly flow at the terminal is expected to switch NE around 06Z tonight, gusting to 25-30 kt. SW winds return after 12Z and winds will gradually subside late Tuesday morning to 5-10 kt. Winds will increase again late Tuesday evening to 10-15 kt, gusting to 20-30 kt.

29/15

MARINE

A strong cold front will move across area waters early this morning, with strong west winds through the Strait of Juan de Fuca and coastal waters. Winds will taper off into the late morning behind the cold front, though seas will remain elevated between 9 to 14 feet.

The next system arrives late Tuesday night into Thursday, bringing moderate to heavy rain that may locally reduce visibilities at times, breezy southwest winds that may reach gale force, and elevated seas above 10 feet.

Seas will ease into Friday to around 4 to 6 feet, where they will remain through much of the weekend. Another system will increase seas and winds early next week.

15

HYDROLOGY

A strong atmospheric atmospheric will continue to move through the Pacific Northwest through Wednesday, bringing significant heavy rainfall across the area. 72-hour precipitation amounts between Monday and ending Thursday morning will likely reach 2 to 6 inches across the lowlands, with 6 to 10 inches over the Olympics and Cascades with locally higher amounts up to 12 inches over the central and southern Cascades.

Rivers continue to rise across the region, with numerous flood warnings in effect. Consult weather.gov/seattle for the latest. While some uncertainty does still remain in regards to the exact flood levels and stages through the next week, many river forecast points are projected to reach major flood stage in the days ahead. 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 this morning to 1 PM PST this afternoon for Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-San Juan County.

PZ...Small Craft Advisory until 7 PM PST this evening for Grays Harbor Bar.

Gale Warning until 4 AM PST early this morning for Admiralty Inlet-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- Northern Inland Waters Including The San Juan Islands- Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 7 PM PST this 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-West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 7 AM PST this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.