Winter 2015/16: A Turning Point in ENSO-Based Seasonal Forecasts

The ocean-atmosphere coupled mode known as the El Nino-Southern Oscillation is considered the dominant mode of global climate variability and is the cornerstone of operational seasonal climate forecasts issued worldwide. Producing accurate seasonal forecasts remains a challenge, but with a record-strong El Nino in the fall and winter of 2015/16, winter seasonal predictions should have been afforded a rare opportunity to showcase forecast accuracy, especially across the North American continent. However, winter 2015/16 forecasts are not noteworthy for their success but rather for their flaws. The inability of the global climate models to predict large-scale climate anomalies likely results from the models' over-sensitivity to tropical forcing. We argue that Arctic influences were also important in causing the observed weather patterns of winter 2015/16, in particular, diminished Arctic sea ice cover, extreme warm Arctic temperatures, and extensive Siberian snow cover. The weak response of the models to Arctic forcing contributed to seasonal forecast errors. To improve seasonal climate forecasts, we recommend complementing the influence of the tropical ocean with contributions from Arctic factors.