would/ was going to

[joham]

I thought it was going to rain/ it would rain but then the sun came out.

Do both tenses work as well in this context? Any differences?

Thank you.

[Clare James]

Both of these sentences are grammatically accurate.

There's a very slight difference between these sentences - If you say 'I thought it was going to rain' then it's because there was some evidence to make you think this. Maybe the sky was black...
In the second form, 'I thought it would rain...' there wasn't any visible evidence to make you think this - you just thought that it was possible or likely.

But the difference is very small here for reported speech!