when it is raining 和 when it rains, 好象都能用,

一般来说都是用when it rains来做从句,表示下雨会的情况下会如何.
比如:when it rains,i will go home.
when it is raining用的不多,表示强调下雨的同时.
比如:when it is raining,the sky becomes dark.