How do I say when there is no rain.

“…yet.”. British people.

They’re both good but I’d say “It’s not raining”.

The title of your post needs some work as well. "*What* do I say when there is no rain?" works, but "what do I say when it isn't raining" sounds more natural.

both are fine and mean virtually the same thing :)

Either are perfectly fine and I don’t hear any distinction between them when I say them out loud.

https://youtu.be/vugqRAX7xQE

Either is fine. I'd say they're both equally used and understood. It would just be a matter of what you would like to say. If someone asked me "Is it raining?" I would probably say "it's not raining" just so the NOT is emphasized, since they asked if it IS raining. But as I said, "It ISN'T raining" is just as good, as long as you're emphasizing it (if this was the answer to a question).

Like the others have said, both are fine! I think I use both in real life.

Both are good. Alternatively you could say "It's sunny."

It’s the same sentence contracted two different ways. Original: It is not raining. It + is: It’s not raining. Is + not: It isn’t raining.

or you could say that it's clear but yours make more sense

Both are grammatically correct and mean the same thing. You can use either one.