El Niño-Southern Oscillation and snow level in the western United States

Abstract

[1] The relationship between El Nino–Southern Oscillation and the elevation of snow level in the western United States is established. Snow level variability is quantified from records of (1) wet-bulb zero heights at ten rawinsonde sites (1957–2010), (2) empirically estimated snow levels over ten adjacent watersheds from precipitation and snowfall observations (∼1924–2009), and (3) 850–700 hPa thicknesses (1948–2010). The statistical relationship between these variables and the Southern Oscillation Index is established through the examination of the change in the empirical probability density function from moderate values of the Southern Oscillation Index to extreme values of the Southern Oscillation Index. For all data sources, results suggest that El Nino events are linked to higher snow levels across much of the western United States. Considering the known effects of El Nino on airflow over the western United States, the elevated snow levels are likely due to the more maritime characteristics of midlatitude cyclones. The strength of this signal decreases with distance from the Pacific Ocean and the southern Rockies display slightly decreased snow levels during El Nino events, likely due to the transition of maritime air masses to continental air masses. A snow covered area analysis derived from the Terra MODIS observations supports this El Nino signal in snow level. There is little evidence for a significant and spatially coherent La Nina relationship with snow level. This ENSO signal in snow level is apparent in the data with trend removed and for the cold and warm phases of the Pacific Decadal Oscillation.