Whether investigating hydrologic conditions, biogeographic issues or climate and global change studies, accurate and accessible information concerning snow extent and depth are extremely valuable. At Rutgers, we continue to populate a snow cover database for Northern Hemisphere lands. Satellite data from visible sensors provides data on snow extent, while extent and depth data are gleaned from satellite microwave and ground station observations. Maps and tabular data may be viewed at http://climate.rutgers.edu/snowcover. In this paper, this snow information will be used to explore the variability of snow cover on seasonal and annual time frames.

As first reported in 1990 (Robinson and Dewey, 1990), snow cover since the late 1980s continues to be less extensive than during the majority of the earlier satellite era. The decrease is concentrated from late winter to early summer, and is observed on both Northern Hemisphere continents. Embedded within this stepwise change is considerable variability at intra and inter annual scales. For instance, near record low snow extents were observed in February and March 2002, and a record low was reached in July. The former two months ranked 3rd and 2nd lowest, respectively, based on 36 years of observations dating back to 1967. A very different picture emerged late in 2002, with snow cover in October, November and December ranking among the top 5 highest over the satellite era. The October positive anomaly of 5.2 million sq. km., 28% above average, is the second largest anomaly in terms of absolute snow area on record for any month since observations began in November 1966.

Variability has a spatial dimension as well. Anomalies of Eurasian and North American snow extents are not always in synch. For instance in 2002, January cover was extensive in Eurasia but low in North America. Both were low in February, but the January pattern was reversed in March. The fall 2003 snow season began early in Eurasia but late in North America, as witnessed by September anomalies. Both continents had extensive October and November covers, while December cover was a record maximum in Eurasia and the 6th lowest on record over North America.

Continued study is needed to better understand the relationship of snow variations with other climate variables. For instance, might the extensive Eurasian snows of fall 2003 be linked with considerable storminess and result low ice extent within the Arctic the previous summer?