Flood in Grays Harbor County, Washington

The Satsop River hit flood stage on the 2nd and Moderate flood stage on the 3rd. Flooding on the Chehalis River at Porter started on the 5th, cresting above Moderate flood before falling below flood on the 11th. Urban and small stream flooding occurred as well.

From December 29 - January 16, a strong and persistent Aleutian Low pressure system developed in the eastern Pacific which directed the jet stream and primary storm track at Washington State that resulted in a rapid 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 the episode, 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 December 29, 2020 and January 7, 2021, resulted in 8 major rivers exceeding flood stage; with 4 of them exceeding moderate flood.