Snow is precipitation that forms when water vapor freezes. Because snow is so reflective, it plays an important role in regulating climate: it reflects incoming sunlight back into space, cooling the planet. Snow also supports life. Melting of seasonal snow (as well as glaciers) provides water for drinking and irrigating crops in many parts of the world. Snowmelt moisturizes soil and reduces the risk of wildfire. Too much snow, however, can lead to springtime floods when the snowpack melts. These snow cover maps are made from observations collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Snow cover values range from medium blue (greater than 0 percent) to white (100 percent). Landmasses that do not sustain snow cover and places where MODIS did not collect data are gray. Because MODIS relies on visible light to assess snow cover, the sensor cannot collect data over the highest latitudes of the Northern Hemisphere during winter when no sunlight reaches those regions. Snow and ice cover most of the Earth’s polar regions throughout the year, but the coverage at lower latitudes depends on season and elevation. High-altitude landscapes such as the Tibetan Plateau and the Andes and Rocky Mountains maintain some amount of snow cover almost year round. Land area is larger and snow cover is more variable in the Northern Hemisphere than in the Southern Hemisphere. NASA
