Woodson Lees Ferry WY flow forecast

This streamflow forecast uses a machine learning (random forest) model trained on Reclamation annual natural flow for the Colorado River at Lees Ferry, AZ for water years 1921-2023 as the predictand and predictors including Pacific Decadal Oscillation (PDO; https://www.ncei.noaa.gov/pub/data/cmb/ersst/v5/index/ersst.v5.pdo.dat) index, Atlantic Multidecadal Oscillation (AMO; https://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v5/index/ersst.v5.amo.dat) index, as well as Community Earth System Model - Large Ensemble (CESM-LE; https://www.cesm.ucar.edu/community-projects/lens/data-sets) precipitation and minimum temperature forecasts. The PDO and AMO predictors are July-August-September averages preceding the start of each water year and the CESM-LE precip. and temp. predictors are October through September averages coinciding with the water year being forecast. E.g., for the 2024 water year forecast (October 2023 - September 2024 total natural flow), PDO and AMO predictors are July 2023 through September 2023 monthly averages and CESM-LE precip. and temp. predictors are October 2023 through September 2024 monthly averages. The random forest forecast is a 600-member ensemble.

The second plot below shows the 'variable importance' for each predictor over the 1921-2023 training period; each variable does add value (this is how the variables were selected), and AMO and PDO have the highest importance.