Heavy rain and low snow levels caused rivers to overflow across Northwestern Washington on Wednesday, closing roads, triggering mudslides and requiring the rescue of at least one man. And in Snohomish County, a mudslide helped a Lake Stevens-area house that had been teetering on the edge of the Pilchuck River to finally fall in. Flooding was expected to ease by early Thursday morning as more dry and frigid conditions settled in — cold weather that might even bring snow to Seattle by week’s end, officials cautioned.