North American snow extent: 1900-1994

Historical fluctuations of North American snow extent from November through March are reconstructed back to 1900 using a combination of satellite and station observations. Using results of principal components analyses (PCA) from a companion study (Frei, A. and Robinson, D.A. Int. J. Climatol., this volume), simple and multiple linear regression models are used to take adv antage of the spatial coverage of satellite observations and the temporal e xtent of station observations. This analysis more than triples the remotely -sensed record length, which begins in 1972. Model results indicate that North American winter snow extent tended to inc rease between the 1930s and around 1980, followed by a subsequent decrease during the 1980s. Long-term trends during November are less dramatic, with small increases since the 1960s. During March a different signal is observe d, with snow extent decreasing since the 1950s. These results suggest a pos sible shift in the snow season. Historical signals from smaller regions within North America are identified during December and January. During December, the continental-scale signal is driven mainly by fluctuations over the western US, while January fluctu ations are more strongly driven by an eastern signal. Models are sufficiently accurate to estimate changes in interannual variabi lity over North America only during February, as well as over the eastern p ortion of the continent during December and January. Continental-scale inte rannual variability during February has been high since the mid-1970s compa red to any previous time this decade. Regional-scale interannual variabilit y over eastern North America in January has also been higher in recent year s, but in December the highest interannual variability occurred during the 1940s. Copyright (C) 1999 Royal Meteorological Society.