North American snow extent: 1900-1994

Abstract

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 advantage of the spatial coverage of satellite observations and the temporal extent 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 increase 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 observed, with snow extent decreasing since the 1950s. These results suggest a possible 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 fluctuations are more strongly driven by an eastern signal. Models are sufficiently accurate to estimate changes in interannual variability over North America only during February, as well as over the eastern portion of the continent during December and January. Continental‐scale interannual variability during February has been high since the mid‐1970s compared to any previous time this decade. Regional‐scale interannual variability over eastern North America in January has also been higher in recent years, but in December the highest interannual variability occurred during the 1940s. Copyright © 1999 Royal Meteorological Society

Spatio‐temporal variability of Great Lakes basin snow cover ablation events

“…Dyer and Mote () did examine the seasonal timing of collective North American ablation events, detecting a shift towards an earlier onset of ablation during the 1960–2000 period. This supports decreasing trends of snow cover in the spring across the continent (Dyer & Mote, ; Frei, Robinson, & Hughes, ). In light of this conclusion and understanding the importance of snowmelt to the hydrology of the Great Lakes basin, it is critical to understand when and where ablation events are occurring specifically in the Great Lakes basin, and if there are significant changes to their seasonal timing.…”

“…Multiple studies have noted a change in the seasonal cycle of snow cover and ablation in diverse regions over North America, with snow cover exhibiting decreasing trends during the spring months, tending towards earlier snowmelt (Brown, ; Dyer & Mote, ; Dyer & Mote, ; Frei et al, ; Frei & Robinson, ). In this study, no significant shift in the seasonal cycle of all monthly snow ablation events is detected for the Great Lakes basin.…”

Trends in wintertime climate in the northeastern United States: 1965–2005

“…Improved quantification of trends in regional snow cover extent are necessary to better understand the region's sensitivity to changes in surface albedo. Satellite imagery combined with station observations revealed a decreasing trend in spring snow cover extent over North America since the 1980s [ Frei et al , 1999]. Future work will focus on identifying trends in snow cover area through the use of daily snow cover maps available at the Rutgers University Global Snow Lab, and comparing the satellite‐derived trends to snow cover output from regional climate models of the northeastern United States.…”

Arctic Radiative Fluxes: Present-Day Biases and Future Projections in CMIP5 Models

“…Note that modeled snow cover area fraction is not the same as snow cover frequency of occurrence. Other studies have converted snow cover area fraction to frequency of occurrence using a binary system with a cutoff of 50% (Frei et al 1999;Henderson and Leathers 2010), and when we apply a similar conversion, snow cover area fraction is similar to frequency of occurrence as discussed in section 3b. Regardless, snow cover area fraction was not available from all CMIP5 models; some of the models output snow depth and/or snow area density instead.…”

“…Across the Arctic basin (608-828N) over the years 2000-08 from March through September, the CMIP5 snow cover area extent for the four models available ranges from 31% to 37%. When converting model monthly-average output to snow frequency of occurrence by requiring 50% snow area extent as was done in other studies (Frei et al 1999;Henderson and Leathers 2010), the modeled snow frequency of occurrence ranges from 31% to 39%, while the MEaSUREs snow cover frequency is 65%. This suggests that the positive CMIP5 net TOA downward SW clear-sky flux biases present over land areas with snow may be at least partially explained by insufficient snow cover extent.…”