Question

Will it rain if the humidity is low?

Answer 1

It can.

Explanation:

Rain forms in clouds not on the ground. The humidity in a cloud is 100%, but the humidity at the surface of the Earth does not have to be. This question then becomes will the rain reach the surface?

Rain falling through air that has a low humidity will lose some of it's water content to the air, via evaporation. Depending on how thick the layer of atmosphere with the low humidity is, and depending on how large the rain drops are will determine if rain hits the ground or if the rain fully evaporates. If the rain fully evaporates we refer to the rain in the air as virga.

I hope this is not too confusing.