Heavy rainfall elevates flood threat across western Washington

Western Washington is bracing for several days of heavy rain and rising rivers as a powerful storm system sweeps into the state. Meteorologists warn local rivers could flood in parts of King County starting Wednesday.

An atmospheric river is driving the weather, a long stream of moisture moving from the ocean toward the Pacific Northwest. The system is drawing humid air, causing steady rainfall, according to the National Weather Service (NWS)

Heavy rain and rising snow levels

The lowlands around Puget Sound could see one to two inches of rain by the end of the week. Higher elevations in the mountain will likely get four to eight inches of rainfall, according to KIRO 7 Meteorologist Nick Allard.

Warm air from the storm is also expected to raise snow levels above 8,000 feet, meaning precipitation that would usually fall as snow in the mountains will instead fall as rain at many elevations.

Rainfall on the snowpack can speed up snowmelt and increase runoff into rivers and streams. That combination of heavy rain and premature melting is expected to raise the risk of flooding later in the week, according to the NWS.

Rivers at risk of flooding

Water from the Tolt River flows into the Snoqualmie River, which may reach moderate flood levels near Carnation as runoff moves downstream.

The Snohomish River could reach moderate flooding by Thursday morning. In contrast, flooding may develop later in the week along the Skagit River as runoff continues to move north through the watershed.

Residents living near rivers and in flood-prone areas are encouraged to monitor conditions closely, as water levels can rise quickly when rainfall intensifies.

The storm may also create dangerous conditions in the mountains. Heavy rain on an unstable snowpack could keep avalanche danger high across parts of the Cascade Range, according to the Northwest Avalanche Center.

Wind may increase across western Washington as the storm moves through. Forecasters say gusts between 20 and 30 miles per hour are possible at times, although widespread wind damage is not expected.