SEATTLE — Rain will clear up Friday morning in western Washington as an atmospheric river begins to move out of the area in time for the weekend.
Atmospheric rivers are bands of atmospheric moisture that transport large amounts of water from the tropics and subtropics northward. They are the largest "freshwater" rivers in the world and can lead to major flooding when they stall over an area for several days.
The weather system broke a daily rainfall record for Seattle on Thursday, according to the National Weather Service (NWS).
By 8:30 p.m. Thursday, 1.58 inches of rain had fallen at Sea-Tac Airport breaking the daily record of 1.53 inches set in 1982. But the rain kept falling. By midnight, the NWS reported a total of 1.99 inches of rain had fallen at Sea-Tac Airport, making Thursday the “wettest October day since the all time wettest day in Seattle history (5.02" Oct. 20th, 2003).”
River flooding from the recent heavy rain is expected to continue Friday and into the weekend as rivers crest over the next 12-18 hours and begin receding.
Flood Warnings for multiple rivers are in effect Friday, including the Stillaguamish River, the Skykomish River, the Skagit River, the Snohomish River and the Snoqualmie River which are all expected to cause minor to moderate flooding.
A Flood Advisory is in effect for parts of King, Lewis, Pierce and Thurston counties.
Heavy rain combined with fallen leaves led to flooded roads Thursday, which may continue into Friday morning.
The heavy rain will also increase the risk of landslides across the Puget Sound region. A slide was reported on SR 20 on the North Cascades Highway Thursday evening. The highway was shut down for the night between mileposts 134 and 171 due to heavy rainfall through Friday morning.