Mean and extreme semi-monthly northwestern hemispheric snow boundaries from satellite records (1966-1979) and some surface data comparisons

Using twelve years of weekly snow and ice boundary charts produced by the National Environmental Satellite Service, mean and extreme positions of the most northerly continuous snow boundary were determined for the beginning and middle of each month over the northern hemiphere. Standard deviations of the latitudinal positions of the boundary at five degree longitudinal intervals were determined to analyse snow-boundary variability. The seasonal advance and retreat of snowcover boundaries deduced from satellite data was compared with that depicted by conventional analysis based on surface observing stations. Based on these analyses, the variability of snowcover on a regional basis is discussed, as is the use of the results to monitor anomalies in seasonal snowcover on a near real-time basis. Major differences between satellite and surface station analyses, which occurred in areas like the North Ameriacan Cordillera, are described and related to terrain and other factors.