Northern Hemisphere Continental Snow Cover during Transitional Seasons: Linking the Arctic and Midlatitudes

Snow cover demonstrates some of the most noteworthy inter-seasonal variability in the climate system. Over 45 million square kilometers of Northern Hemisphere continental lands are snow covered for a time during the winter while being snow free during summer. There has been no discernable long-term change in the extent of snow in either of these seasons during the more than 50-year era of satellite snow monitoring. This is not the case during the transitional seasons. This presentation will discuss how spring snow extent declined in the late 1980s and early 1990s and has generally remained lower than the early satellite era since that time. A consistently reduced coverage of snow has occurred in May and June over the past 10-15 years than at prior times during the satellite era. Meanwhile it has become increasingly apparent that fall snow extent has shown a marked increase in the past 10 years, particularly in October and November. How these transitional season variations are associated with other climatic variables is not yet well understood. This includes uncertainties as to whether changes in snow extent, or the lack thereof, may be influencing or responding to other climate system components. Suffice it to say that it is important to recognize these ongoing changes in snow extent during transition seasons as efforts are made to better understand Arctic -Mid-latitude linkages.