The Influence of El Niño and La Niña on Winter Climate Conditions at 138 Ski Resorts in Western North America

Abstract:

This research examines the effect El Niño and La Niña have on the climate conditions of 138 ski resorts in western North America. Using ClimateWNA, monthly values for snowfall and degree days < 0°C (a measure of winter season coldness) were generated for the mid-slope elevation of the resorts for the primary ski season months of December, January, February, and March. From this data, composite values were computed by summing the four months analyzed for each of the two variables, with the December value coming from the previous year. Regression analysis was used to see if a relationship exists between the two climate variables and a summed composite of the monthly Southern Oscillation Index (SOI) for the same four months. Correlation coefficients were determined by regressing the observations for the time period 1935 to 2012. The correlation coefficients were then mapped using ARCGIS to display possible spatial patterns across the study area. Different map symbols were used to identify whether the correlation coefficient was positive or negative, and whether it fell within four levels of statistical significance: P ≥ 0.01, P < 0.01, P < 0.001, and P < 0.0001. Correlation coefficients with probability values equal to P ≥ 0.01 were considered not significant on the map. For the variable degree days < 0°C, resorts located in British Columbia, Alberta, Washington, and coastal south Oregon generally had warmer than usual winters during El Niño events and colder winters when SOI values suggested the occurrence of La Niña. A single resort, Ski Apache in New Mexico showed the opposite trend. Snowfall was found to be higher during La Niña events and lower with El Niño events for a number of resorts above 42° N latitude. Further, the strength of these correlations generally decreased with distance from the coast. Resorts in New Mexico and Arizona generally had more snowfall with El Niño and less snowfall with La Niña.