Monthly Relationships Between NAO Mode and North American Snow Pack Persistence on a One-Degree-by-One-Degree Grid

Simulations by Klingaman et al. (2008) suggest persistent snow pack over North America could modulate the North Atlantic Oscillation (NAO). To investigate this further, correlation tests for each point on a one-degree-by-one-degree gridded data set covering the years 1956 to 2009 are run comparing the number of days in each of November, December, January, and February where the snow pack was at least 15 cm to the monthly NAO value for each subsequent month up to the following March. Tests are run using two different approaches: a hybrid chi-square/Fisher exact test contingency table scheme and Spearman rank correlations. Significant correlations are noted over five larger-scale areas: a large region of Northwestern Canada and Southern Alaska in November with both two and four-month lags, an area south of James Bay in December with a one-month lag, the Central Appalachians in January with a one-month lag, the vicinity of the Alaska Panhandle in January with a two-month lag, and an area in the Southwest United States in February with a one-month lag. For each of these correlations, 500 mb and 700 mb geopotential height anomaly maps are generated using the NCEP/NCAR reanalysis product for composite high and low snowpack months. These maps are examined for evidence of snow pack forcing of the overall upper air pattern and therefore the NAO. Results do not support this relationship.