1. I put off my departure on account of a heavy rain. (X)
This sentence comes from Qian Gechuan, a Chinese scholar. But the "a" here is not correct semantically, is it?
3. A rain was forecast for this morning, but I didn't take it seriously. (X)
4. Rain had been forecast for this morning, but I didn't take it seriously.
Sentence3 is wrong. Is the reason the same with 1? Could "A heavy rain" for 3 make it correct? and what about "Heavy rain" for 4, could it be still correct?
5. There wasa heavy rain in California last night.
6. There was heavy rain in California last night.
"A heavy rain" would mean it it will rain in some parts of CA while "heavy rain" would mean it will rain in all parts of CA. Thus, 5 is not meaningful most of the time, right? What're the common meanings of "A heavy rain" and "heavy rain"?
Many thanks in advance.