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.

Flood in LEWIS, WASHINGTON
From 13-JAN-21 02:45:00 to 13-JAN-21 23:15:00 (PST-8)
Location: CHEHALIS RIVER AT CENTRALIA
Flood cause: Heavy Rain
Property damage: 1.45M
Crop damage: 0.00K
Reported by: River/Stream Gage

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

Flood in GRAYS HARBOR, WASHINGTON
From 12-JAN-21 11:30:00 to 16-JAN-21 09:00:00 (PST-8)
Location: BRADY
Flood cause: Heavy Rain
Property damage: 59.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Satsop River near Satsop and Chehalis River at Porter exceeded flood stage. Urban and small stream flooding also occurred.

Flood in JEFFERSON, WASHINGTON
From 12-JAN-21 08:00:00 to 12-JAN-21 15:00:00 (PST-8)
Location: HOH
Flood cause: Heavy Rain
Property damage: 554.00K
Crop damage: 0.00K
Reported by: County Official

Heavy rain caused surface runoff, landslides, and urban and small stream flooding. One to three inches of rain fell during the day.

Flood in MASON, WASHINGTON
From 13-JAN-21 01:45:00 to 14-JAN-21 03:20:00 (PST-8)
Location: MATLOCK
Flood cause: Heavy Rain
Property damage: 5.44K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Skokomish River exceeded moderate flood stage. Urban and small stream flooding occurred as well.

Flood in KING, WASHINGTON
From 12-JAN-21 08:00:00 to 14-JAN-21 09:15:00 (PST-8)
Location: DUVALL
Flood cause: Heavy Rain
Property damage: 474.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Snoqualmie and White Rivers exceeded flood stage. Urban and small stream flooding occurred as well. Heavy rain caused some landslides.

Flood in SNOHOMISH, WASHINGTON
From 12-JAN-21 08:00:00 to 14-JAN-21 20:45:00 (PST-8)
Location: INDEX
Flood cause: Heavy Rain
Property damage: 329.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Snohomish, Skykomish, and Stillaguamish Rivers exceeded flood stage. Urban and small stream flooding also occurred.  Heavy rain caused some landslides.

Flood in THURSTON, WASHINGTON
From 13-JAN-21 01:45:00 to 15-JAN-21 07:45:00 (PST-8)
Location: ROCHESTER R AND K AR
Flood cause: Heavy Rain
Property damage: 63.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Chehalis River near Grand Mound and Skookumchuck River near Bucoda crested above moderate flood. Urban and small stream flooding occurred as well.