Diagnosis of anomalous winter temperatures over the eastern United States during the 2002/03 El Nino

The eastern United States experienced an unusually cold winter season during the 2002/03 El Nino event. The U. S. seasonal forecasts did not suggest an enhanced likelihood for below-normal temperatures over the eastern United States in that season. A postmortem analysis examining the observed temperatures and the associated forecast is motivated by two fundamental questions: what are these temperature anomalies attributable to, and to what extent were these temperature anomalies predictable? The results suggest that the extreme seasonal temperatures experienced in the eastern United States during December-February (DJF) 2002/03 can be attributed to a combination of several constructively interfering factors that include El Nino conditions in the tropical Pacific, a persistent positive Pacific-North American (PNA) mode, a persistent negative North Atlantic Oscillation (NAO) mode, and persistent snow cover over the northeastern United States. According to the simulations and predictions from several dynamical atmospheric models, which were not rigorously included in the U. S. forecast, much of the observed temperature pattern was potentially predictable.