On the seasonal prediction of the western United States El Niño precipitation pattern during the 2015/16 winter

However, during the strong El Nino of 2015/16, the WUS winter precipitation pattern was roughly opposite to this canonical (average of the record) anomaly pattern. To understand why this happened, and whether it was predictable, we use a suite of high-resolution seasonal prediction experiments with coupled climate models.

We find that the unusual 2015/16 precipitation pattern was predictable at zero-lead time horizon when the ocean/atmosphere/land components were initialized with observations. However, when the ocean alone is initialized the coupled model fails to predict the 2015/16 pattern, although ocean initial conditions alone can reproduce the observed WUS precipitation during the 1997/98 strong El Nino. Further observational analysis shows that the amplitudes of the El Nino induced tropical circulation anomalies during 2015/16 were weakened by about 50% relative to those of 1997/98.