Scientist Tom Painter examines the differences between pure and dirty snow. A rise in dust can be a critical influence on snow-fed water supplies in the American West.
This pair of maps shows average percent snow cover in December 2008 and February 2009, the first and last months of meteorological winter in the Northern Hemisphere.
Flying over the Sierras in a Twin Otter aircraft, NASA scientists are finding new ways to measure the amount of water stored in the winter snowpack with greater accuracy than ever before.