Hello. I will be very grateful for some help.

1) Do you think it is possible to say: "Heavy rain started / began", and if yes, is it "heavy rain" or "a heavy rain"?
2) Is it possible to say: "Rain started falling", and if yes, is it "rain" or "the rain"?
3) Is it possible to say: "there was heavy rain"?
Thank you very, very much.

1) Yes. Either is correct, but a heavy rain is better.

2) Either is correct.

3. Yes.

Hello! I'm here to help. Let's go through your questions one by one:

1) Do you think it is possible to say: "Heavy rain started / began", and if yes, is it "heavy rain" or "a heavy rain"?
Yes, it is possible to say "Heavy rain started / began." In this case, "heavy rain" is the correct phrase to use. When describing weather conditions, we often use uncountable nouns, so we do not use an article like "a" in front of it. We can simply say "heavy rain" to refer to a significant amount of rain.

2) Is it possible to say: "Rain started falling", and if yes, is it "rain" or "the rain"?
Yes, it is possible to say "Rain started falling." In this case, both "rain" and "the rain" can be used depending on the context. If you are referring to rain in general as a natural phenomenon, you can use "rain" with no article. However, if you are referring to a specific instance of rain that has been previously mentioned or is known to both the speaker and the listener, you can use "the rain."

3) Is it possible to say: "there was heavy rain"?
Yes, it is possible to say "there was heavy rain." In this case, "heavy rain" is used as a noun phrase to describe a specific type of rain. By using "there was," you are indicating that heavy rain occurred at a certain point in time.

I hope this explanation helps! If you have any more questions, feel free to ask.