How is the national area covered by snow and snow depth measured?

Dear Tom,
How is the national area covered by snow and snow depth measured?
Heinz Grob, Chicago
Dear Heinz,
The daily national snow cover data for the Lower 48 is provided by NOAA’s National Operational Hydrologic Sensing Center, an agency that has been documenting the national snow cover since September 2003. The daily percent of coverage and depth of the snow is derived from a combination of ground-based, airborne and satellite data. Since 2003, the highest national snow coverage on record was 70.9 percent measured on Jan. 12, 2011. The national snow cover map for that date revealed that snow covered the ground in portions of 47 of the 48 states, with only Florida snow-free. Chicago’s contribution to the record was a four inch snow cover, buoyed by a 5.9 snowfall the previous day.

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