Pacific sea surface temperature and the winter of 2014

It is shown from historical data and from modeling experiments that a proximate cause of the cold winter in North America in 2013-2014 was the pattern of sea surface temperature (SST) in the Pacific Ocean. Each of the three dominant modes of SST variability in the Pacific is connected to the tropics and has a strong expression in extratropical SST and weather patterns. Beginning in the middle of 2013, the third mode of SST variability was two standard deviations positive and has remained so through January 2015. This pattern is associated with high pressure in the northeast Pacific and low pressure and low surface temperatures over central North America. A large ensemble of model experiments with observed SSTs confirms that SST anomalies contributed to the anomalous winter of 2014.