January 2011 was marked by a series of crippling snow storms across the
United States. By January 12, about 71 percent of the country had snow on
the ground, the fifth-largest snow cover extent in the last 45 years. This
image, made with data from the Moderate Resolution Imaging Spectroradiometer
(MODIS) on NASA’s Terra satellite (from the monthly snow cover product), shows the maximum snow
cover for the month. The image shows that every state in the contiguous
United States, with the exception of Florida, got snow in January.
The image provides a gauge for both snow extent and the length of time
snow stayed on the ground. Areas that are white in this image were entirely
covered with snow for most of the month. Pale green areas had snow for just
part of the month or were only partly snowy, with areas of exposed ground.
Dark green areas are places where MODIS did not observe snow during the
month. The sensor does not see through clouds, so it does not see snow that is only on the
ground on cloudy days.
With all the snow, it would be easy to think that the United States
received plenty of winter moisture, but snow is deceptive. It takes about 10 inches of fresh snow to make an inch of liquid water when it melts. The winter storms brought more snow, but less rain to much of the United
States, said the National Climatic Data Center. January 2011 was the ninth-driest January in the United States in 117 years. The southern half of the
country was particularly hard hit. New Mexico experienced its driest January
Satellite snow cover measurements, like this one, play an important role
in helping scientists measure trends in snow cover and how snow influences
Earth’s climate. Satellite measurements show that, despite the snow in
January 2011, snow cover extent has dropped on average across the Northern
Hemisphere in the last 30 years. Recent
research indicates that the drop in snow cover is contributing to warmer
temperatures in the Northern Hemisphere.