Raining Cats and Dogs is a mod that lets you make any animal rain out of the sky with lots of in-game configuration.
When you first load a world it will rain cats and dogs. You can configure the rain with these commands
/rainingcatsanddogs - Get a list of all commands
/rainingcatsanddogs check - Checks all the values of the settings
/amount {number} - Changes the Amount that summon (Default is 2)
/radius {number} - Changes the Radius in which the mods can summon (Default is 50)
/frequency {number} - Changes how often the mobs summon in ticks (Default is 3 [20 ticks in one second])
/type {string} - Changes the mob that spawns (Default is default, which summons cats and dogs)
/type {type} {string} - Changes the NBT data of the entitys that spawn (Default is nothing [Don't put {}, use commas to seperate])
/height {number} - Changes the height at which the mobs fall from (Default is 100)