Subseasonal Prediction of Precipitation over California in the Winter of 2016

The main player of winter weather of 2015-2016 was the record-breaking ENSO event in the tropical Pacific Ocean. Successful seasonal prediction of this ENSO event together with statistical analysis of the past ENSO events led to belief that this event would greatly ease the drought in the US western coast and particularly the California regions. However, negative precipitation anomalies persisted over the entire winter instead. So why this ENSO event failed to deliver expected rainy winter over California? To understand this issue, we examine weather anomalies using the recently available realtime ensemble forecast dataset from the Subseasonal to Seasonal (S2S) Prediction project. A variety of ensemble composites have been made to infer the origins of the California weather anomalies in the past winter. The strongest signal emerging from this analysis is negative correlation of January precipitation anomalies between California and the eastern Pacific Ocean, suggesting tropical origin of the California weather anomaly.