Weather

Rain (or snowstorms in snow biomes) were added in version 1.2 of Terraria. The rain is normally slanted as if wind is blowing it and is blocked off by blocks above. Certain creatures only spawn when it is raining on your world.

Creatures
Creatures that can spawn in rain are:
 * Umbrella Slime
 * Flying Fish

Update Info
v1.2
 * Added to the game.