Subject: How does humidity affect the formation of rain/snow (precipitation)?

The water cycle creates clouds and, therefore, precipitation. Clouds are formed by evaporating water which also describes humidity. Yet I don't understand how precipitation correlates specifically with humidity in an area. To search deeper into the question, I would like to know how humidity affects the formation of cumulonimbus and nimbostratus clouds which are the two precipitation bearing clouds. Even understanding this, I still do not understand how humidity must change in order to form these different clouds? I wonder what conditions must occur for theses types of clouds to form, besides evaporated, transpirated, H2O vapor that cools to its dew point, forming clouds and then perhaps changing ino a precipitation cloud? Please help me to better understand these facts.

Re: How does humidity affect the formation of rain/snow (precipitation)?