Role of the Tropics and its Extratropical Teleconnections in State-Dependent Improvements of U.S. West Coast UFS Precipitation Forecasts | CU Experts

Boreal-wintertime hindcasts in the Unified Forecast System with the; tropics nudged toward reanalysis improve United States (U.S.) West Coast; precipitation forecasts at Weeks 3-4 lead times when compared to those; without nudging. To diagnose the origin of these improvements, a; multivariate k-means clustering method is used to group hindcasts into; subsets by their initial conditions. One cluster characterized by an; initially strong Aleutian Low demonstrates larger improvements at Weeks; 3-4 with nudging compared to others. The greater improvements with; nudging for this cluster are related to the model error in simulating; the interaction between the Aleutian Low and the teleconnection patterns; associated with the Madden-Julian oscillation (MJO) and El Niño-Southern; Oscillation (ENSO). Improving forecasts of tropical intraseasonal; precipitation, especially during early MJO phases under non-cold ENSO,; may be important for producing better Weeks 3-4 precipitation forecasts; for the U.S. West Coast.

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