Clouds like these over Canyonlands National Park, Utah, are one of our primary weather indicators. Clouds and rain are generally formed in low pressure weather systems. In these areas of low pressure, air rises and then cools during ascent. When water vapor cools it condenses into water droplets or even ice crystals. If dense cloud cover lasts, water droplets or ice crystals grow and produce rain and snow. In temperate climates, rain may start out as snowflakes and eventually melt during their descent to the ground.
There are ten types of clouds associated with cirrus, cumulus and stratus clouds. Nimbostratus clouds are pictured here, a strong indicator of imminent rain.