by Anita Silverman
One of the many ways NOAA (National Oceanic and Atmospheric Administration) measures snow cover is with satellites. Some of the primary data sources for detecting snow cover are the polar orbiting satellites (POES) and geostationary orbiting satellites (GOES). Visible and Infrared pictures from these satellites can show snow/ice boundaries very well, as long as there is no cloud cover. Microwave detecting satellites are unobstructed by clouds and thus can be used as another observational tool. Ultimately, the most accurate map can be produced by comparing and contrasting information from several sources.
The first Northern Hemisphere Weekly Snow and Ice Cover analysis was generated in November 1966 from the visible satellite imagery. However, the weekly update often missed changes in snow cover which occurred on a daily basis, which lead to inaccurate low level temperature forecasts and poor predictions of rainfall versus snowfall. In February 1997, a new Daily Northern Hemisphere Snow and Ice Cover chart was introduced (see Picture 1). This analysis used existing satellite imagery and surface observations. The resolution of the chart was improved in early 2004 (see Picture 2), when technology allowed the creation of a 4 km (2.5 miles) resolution map. At this time, both the 4 km (2.5 miles) and 24 km (15 miles) maps are produced. The product is presently used as an operational input into several National Weather Service computer weather prediction. 
Picture 1. Snow and Ice Cover chart from Dec. 24, 1997 Picture 2. Snow and Ice Cover chart from Dec. 24, 2004
For the Latest Snow and Ice cover chart go to Operational Daily Snow Cover Analysis. Be sure and look at the United States Graphic 31 Day Animation. You will be able to see the southern edge of the snow advancing south from the Arctic as winter approaches.
 From the Department of Commerce/National Oceanic and Atmospheric Administration/National Environmental Satellite, Data, and Information Service/Office of Satellite Data Processing and Distribution/Scientific Services Division