World's largest hot desert. Located in north Africa and covers over 3,500,000 square miles (9,000,000 sq km) or roughly 10% of the continent. Mean temperature over 30 degrees C. Variations may also be huge, from over 50 degrees C during the day, to temperatures below 0 at night in summer.
Fall begins (Northern H.) History. Fall begins in the Northern Hemisphere when the Sun is perpendicular to the equator. This day has equal hours of day and night. The first day of Fall is also called the Autumnal Equinox. In many areas it coincides with harvests. The first day of Fall happens between each year between September 22 and 24.
Rain develops from cloud droplets or ice crystals; if it starts as crystals, the rain first takes the form of snowflakes, but they melt when they enter warmer layers of air, changing into raindrops. In thunderstorms that have a central updraft capable of hosting both rain and snow, snowflakes fall, but the liquid water freezes together with them, making ice pellets that keep growing as they add more water droplets.