The Pacific Decadal Oscillation (PDO) has been positive (meaning unfavorable warm ocean conditions) nearly every month from January 2014 through December 2019. In fact 2015 and 2016 had the worst positive PDO readings ever recorded.

The first four months of 2020 have all had negative PDO readings indicating favorable ocean conditions for the smolt out migration going on right now. The 2020 terminal Chehalis coho return is forecasted to be 70,000 fish. All things being equal (they never are), the negative PDO could be forecasting a 2021 coho run in the range of 120,000 fish.