Question

why convection current generally lead to rain

Answer 1

because the convection takes place in liquid. when anywhere rain water contain so convection current takes place.

Answer 2

Answer is simple, just assume boiling a water in a pan , when covered wid a lid. then when u open the lid u see tiny droplets on d surface of lid. the rain occurs wide same priciple.
In summer when the weather is hot, water evaporates from ponds rivers and accumulates in atmosphere in form of clouds which causes rain.