Flood in Lewis County, Washington

The Cowlitz River at Randle and Newaukum River near Chehalis exceeded flood stage. Urban and small stream flooding occurred also.

The period from January 10 to 16 continued a pattern of a strong and persistent Aleutian Low pressure system in the eastern Pacific that began December 29, 2020 and which directed the jet stream and primary storm track at Washington State. This resulted in a series of atmospheric rivers and wind storms that battered Washington State. Water vapor transport into Washington State averaged 160-200% of normal during the period from December 29 through January 16. Numerous periods of heavy rain occurred during this period, which in turn resulted in widespread and sustained river flooding, urban and small stream flooding, mudslides, and landslides in addition to the significant and widespread impacts from high winds, pounding surf, and coastal flooding.

During the wettest portion of this 19-day period, Washington State experienced widespread precipitation totals between 200% and 350% of normal. The prolonged bouts of moderate to heavy rain between January 10 and 16, 2021, resulted in 12 major rivers exceeding flood stage, 3 of them exceeded moderate flood.