There is an excellent, very informative presentation of Northern Hemisphere snow cover extent and long term trends and variability up to 2010 (Spring and Fall) and 2011 (Winter) from the Rutgers University Global Snow Lab.
As concluded in the 2007 IPCC WG1 report
“……..snow cover [has] declined on average in both hemispheres. “
The reality of the snow cover trends is more complex, however, as clearly illustrated in the figures presented below. Only the spring shows a decline, and, even then, its decline is dominated by the period prior to 1990.
source of top image in post [for January 2011]