Subseasonal-to-Seasonal Prediction of California Winter Precipitation and the Northern Pacific Jet Stream

Successful seasonal prediction of California winter precipitation has recently been a challenge for global climate models. While ENSO has been assumed to be a dominant driver of winter California precipitation on seasonal timescales, the Niño3.4 Index is not strongly correlated to observed precipitation outcomes. Earlier studies have attributed the lack of skill on seasonal timescales to the inherently low predictability of California winter precipitation, which is dominated by subseasonal internal variability. On the other hand, this internal variability may be predictable on subseasonal timescales, potentially contributing to successful subseasonal prediction. This study explores the observed and modeled relationship between California precipitation and the location and strength of the jet stream over the northern Pacific on subseasonal to seasonal timescales, finding that the anomaly and distribution of California precipitation have a stronger relation to the jet than to ENSO. This relationship is relevant for prediction since more skillful jet forecasts are found to accompany more skillful precipitation forecasts.