Multiensemble Postprocessed and Downscaled Subseasonal-to-Seasonal Forecasting over the Northwestern United States

Accurate and reliable seasonal forecasts are important for energy supply and demand forecasts as well as reservoir release schedules. Here we evaluate forecasts of 2m temperature and precipitation over the Columbia River basin and its sub-basins over the Northwestern U.S. from 0.5 to 3.5 lead months after post-processing and downscaling 30-year hindcasts from the North-American Multi-Model Ensemble (NMME).

Forecasts derived from each member model as well as a super-ensemble of the models are compared to the ECMWF ERA-Interim Reanalysis and higher resolution PRISM data used in the downscaling process. Deterministic and probabilistic metrics of forecast performance will be analyzed in reference to climatology, detrended climatology, and the raw unprocessed forecasts. Special emphasis will be placed on the potential value of probabilistic vs. deterministic forecasts. Several recent downscaling methods will also be evaluated to determine the strengths and weaknesses of these methods and how the advantages of each method can be leveraged to yield more reliable and accurate forecasts.