It takes a million or so droplets to form a single raindrop. Precipitation can occur by two processes. Clouds are classified based upon their altitude and appearance. Wind is the horizontal movement of air that flows from areas of high pressure to areas of low pressure. Horizontal variations in air pressure result from differential heating of air near the earth's surface by solar radiation.
Air expands when warmed and contracts when cooled.
Contraction results in higher air pressures, expansion results in air occupying a larger area and is accompanied by a decrease in pressure. Highest pressures are associated with high latitudes and lower pressures are found near the tropics. The greater change in pressure between two points the greater the wind velocity. If pressure differences represented the only control over wind direction, wind would blow perpendicular to the isobars. The Coriolis effect occurs because of the difference in the velocity of Earth's rotation with latitude.