Here is no cloud in the sky. It --------- a lovely day.
1) will be
2) is going to be
In grammar-related books, there is a common sentence showing the usage of "be going to".
- Look at those clouds. It's going to rain.
However, to me, the OP is different. I think "a lovely day" is a mere opinion, and has nothing to do with "what is likely to happen in the near future". So, both #1 and #2 sound correct to me.
What do you think?