Atmospheric rivers set to dump rain across Western WA

Much of Western Washington was under a flood watch Sunday as a series of atmospheric rivers took aim at the area.

“The big show” will begin Monday, when the largest of the atmospheric rivers arrives, said Steve Reedy, a Seattle-based National Weather Service meteorologist.

Flooding could occur around rivers, creeks and urban areas with poor drainage from Lewis County up to the Canadian border. In King, Snohomish and Skagit counties, Reedy said rivers could reach moderate or possibly major flood stages.

The Skokomish River is likely to flood Sunday night, with other rivers in the region following Monday and Tuesday, according to the weather service, which warns that “extensive street flooding and flooding of creeks and rivers” is possible.

Atmospheric rivers are large swaths of water vapor from tropical areas of the Pacific Ocean that can extend for thousands of miles and bring extensive rain and snowfall. Up to 6 to 9 inches of rain are expected over the Cascades and 8 to 11 inches over the Olympics through early week.

The flood watch, which means meteorologists estimate there’s a 50% to 80% flooding will occur, extends through Wednesday night, with showery weather expected to follow through the rest of the week.

Hundreds of households in the Seattle area lost power Saturday due to rain and wind. Reedy said windy weather could pick back up again in the late afternoon Monday, leading to more localized power outages but likely not anything widespread.

Snow has also been dumping in the mountains. Stevens Pass has received around 40 inches of new snow since Thursday and Snoqualmie Pass around 19. That could turn to rain, setting up avalanche conditions.

The Northwest Avalanche Center forecast high avalanche danger on Sunday at Snoqualmie and Stevens passes.