Evaluating Northern Hemisphere snow cover during the satellite era: variations in extent and associations with temperature

The NOAA/NESDIS weekly map series of Northern Hemisphere snow cover extent has proven extremely valuable toward enhancing our understanding of snow cover kinematics and dynamic relationships between snow and other climate variables. Data from this series, including recently completed reanalyses from the previously suspect late 1966 through 1971 interval and a pseudo-weekly product produced from daily maps that have succeeded the weekly maps after May 1999 are used to create new climatologies, examine snow variability during the satellite era and compare seasonal snow cover and temperature anomalies across Northern Hemisphere lands.

Analyses of the lengthy time series show that snow cover since the late 1980s is less extensive than during the vast majority of the earlier satellite era. The decrease is concentrated from late winter to early summer, and is seen in Eurasia and North America. Snow cover and temperature anomalies show statistically significant associations on an annual basis as well as during the fall and spring. Both anomalies are area averages over the region for which climatological values of seasonal snow cover frequency are between 10% and 90%. Seasonal pairings all show an inverse relationship between the two variables, with correlation coefficients (r) significant at the 95% level in April-May, and at the 99% level in October-November and February-March. The latter has an r of -.57, and is the strongest of all monthly pairings. The annual snow season (October-September) relationship of -.60 is also significant at the 99% level.