The snow cover map shows the fraction of an area covered by snow on a monthly basis. Measurements were made by the MODIS sensor on NASA's Terra satellite. Gray indicates land areas with no snow, darkest blue represents minimal snow cover, and solid white indicates 100 percent snow cover. 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 the polar region.
The rainfall maps show total monthly rainfall in millimeters as recorded by NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite. High rain totals are represented in dark blue, while small rainfall totals are shown in white. TRMM measures rainfall in the tropics. High-latitude regions, where TRMM does not record rainfall, are gray.