On the Relationship between Spring NAO and Snowmelt in the Upper Southwestern US

Abstract

his study examines the relationship between the North Atlantic Oscillation (NAO) and snowmelt in spring in the upper southwestern states of the US (UP_SW) including California, Nevada, Utah, and Colorado, using SNOTEL datasets for 34 years, 1980-2014. We find statistically significant negative correlations between NAO averages in the snowmelt period and timings of snowmelt, i.e., positive NAO phases in spring enhance snowmelt, and vice versa. It is also found that correlations between the El Niño-Southern Oscillation and snowmelt are negligible in the region. The NAO-snowmelt relationship is most pronounced below the 2800 m level; above this level, the relationship becomes weaker. The underlying mechanism for this link is that a positioning of upper-tropospheric anticyclonic (cyclonic) circulations over the western US that are associated with development of the positive (negative) NAO phases tend to bring warmer-and-drier (colder-and-wetter) spring weather conditions to the region. The temperature variations related with the NAO phases also strongly modulate the snowfall-rainfall partitioning. The relationship between NAO and spring snowmelt can serve as key information for the warm season water resources management in the UP_SW.