What causes rain?

Rain is the byproduct of the natural cycle of evaporation and condensation that happens all over the world. Moisture evaporates into the atmosphere from bodies of water and soil. Once this moisture is aloft in the atmosphere, certain conditions cause it to precipitate in the form of rain. These conditions include changes in atmospheric pressure, orographic lift cause by hilly terrain, and changes in temperature. Once the moisture starts to condense into larger and larger droplets, they eventually become heavy enough to fall from the cloud in the form of rain drops. This cycle then continues on with the newly fallen rain beginning to evaporate into the atmosphere.