Weekly Northern Hemisphere Snow Maps: 1966-1999

From October 1966 through May 1999, NOAA satellite meteorologists produced weekly visible-wavelength satellite maps of Northern Hemisphere snow extent. These maps provided an extremely useful means of assessing snow extent from regional to hemispheric scales. Applications utilizing map information include operational weather forecasting, climate change assessment, investigations of linkages between snow cover and Asian monsoons, ENSO, and the NAO, and even exploring relationships between snow cover and bird migration. The weekly maps are no longer produced, having been replaced in June 1999 by daily Interactive Multisensor Snowmap (IMS) initiative maps that rely heavily on visible imagery but also utilize satellite microwave and station data. Also, we have recently reanalyzed the 1967-1971 period, as the original charts from this interval were deemed unreliable.

Therefore, it is appropriate at this time to incorporate all of the weekly data into an updated analysis of hemispheric snow extent. This contribution will include an overview of the production of the snow maps throughout the weekly era. Also presented will be the first 30-year (actually 33 years) climatology of snow at this scale and expanded results of seasonal variations in cover during the satellite era, especially the significant decline in spring snow cover since the late 1980s.