Seasonal Snow Cover and Short-Term Climatic Fluctuations over the United States

Interannual fluctuations of snow cover in the United States are evaluated in the context of short-term climatic variability. The analysis is based on 2.5 and 15.0 cm snow coverage digitized weekly for the winters of 1949–50 through 1980–81. The winter of least snow (1980–81) and the winters of most snow (1977–78 and 1978–79) have occurred in the most recent portion of the record. Considerable persistence of departures from normal snow cover is evident in the monthly lagged autocorrelations, which range from 0.35 in the lee of the Rockies to 0.75 in the Far, West. Fluctuations of surface temperature are most highly correlated with snow cover in a broad east-west band which straddles the normal wintertime position of the snow edge. Snow anomalies in the eastern and western United States are associated with opposite phases of a three-cell field of 760 mb height anomalies over the North Pacific Ocean and North America. A series of regression analyses shows that a portion of the surface temperature variance unexplained by the large-scale (700 mb) circulation can be attributed to snow cover. In the marginal snow zone, this contribution is typically 10–20% of the variance of the concurrent monthly temperature and 5–10% of the temperature variance of the following month. The effect of snow on surface temperature is largest during the late winter.