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.