The Impacts of El Nino on Mid-Atlantic Winter Snowfall with Regards to North American Climate Variability

The impacts of ENSO and North American climate modes on seasonal snowfall in the Mid-Atlantic region are investigated. Particular emphasis is placed on the convergent patterns of El Nino and negative NAO during Northern Hemisphere winter. This study is motivated by the highly anomalous events associated with the 2009-2010 winter season, as well as by a general interest in mid-latitude synoptic variability. Principal sources of Eastern U.S. wintertime climate variability (ENSO, NAO, and PNA) are examined for potential effects on large-scale flow, cyclone activity, temperature and precipitation patterns, and regional snowfall. These findings are used to qualitatively infer the combined influence of El Nino and –NAO within the specified region of interest. A supplementary statistical analysis is conducted to evaluate the hypothesis and provide a quantitative assessment of changes in seasonal snowfall at selected stations. Evaluation of the three climate modes reveals that warm ENSO and –NAO (+PNA) regimes create synoptic environments and temperature anomalies favorable for increased East Coast cyclone activity and winter snowfall. Moreover, results from the statistical analysis indicate that seasonal snowfall in the Mid-Atlantic region is significantly different (higher) during warm ENSO/-NAO winters, as compared to the long-term average (1950-2010).