It is correct and usable in written English. You can use it to describe a situation when it is raining heavily. For example, "The heavy rain kept me from going outside.".
Saturday: 95 with heavy rain.
Then a heavy rain falls.
TOAD-STRANGLER Very heavy rain.
"Limbo and Heavy Rain.
Heavy rain cancels.
Until Heavy Rain.
But the heavy rain stayed away.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union