It’s pouring rain. (Let’s Read and Write in English 3, by Ken Methold and Gillian Flaherty)
Is the above sentence in the present progressive tense?
Yes it is but I think the idiom is ‘it’s pouring with rain’.
I actually think the collocation is ‘in the pouring rain’.
The idiom I use is “it’s pouring down rain”.
The sentence is quoted from a book produced by a company in Australia. Perhaps it’s Australian English usage.
At any rate the sentence is in the present progressive (continuous) tense.
Literature data-bases bear out the distinction rather better than the ngrams do.
I found It’s (or it was ) pouring rain in F.Scott Fitzgerald, Frank Norris, and Alice Hegan Rice, but not in a BE author.
I found It’s (or it was ) pouring with rain in Elinor Glyn, Jerome K.Jerome, Wilkie Collins, Charlotte M. Yonge, D.H.Lawrence, and E.M.Forster, but not in an AE author.
The BE ngram shows a clear preference for pouring with rain .
The AE ngram is more equivocal.
I’m inclined to think that this gives us an insight into how successfully the ngrams manage to separate BE from AE books, rather than that the AE members have been talking nonsense.
Here are the relevant ngrams I found: