This is a good question, because 'nice' is not a very descriptive word, and there are better options. You could look up synonyms for 'nice', but not all of them can be used with climate. And not all sound natural. For example, these are the answers you get from Google:
"enjoyable, pleasant, pleasurable, agreeable, delightful, satisfying, gratifying, acceptable, to one's liking, entertaining, amusing, diverting, marvellous, good, lovely, great, neat"
And these are the ones that I would say are correct and sound natural:
"enjoyable, pleasant, agreeable, delightful, to one's liking, marvellous" (all quite formal)
"good, lovely, great" (more informal)
Don't use "pleasurable, satisfying, gratifying, acceptable, entertaining, amusing, diverting, neat" - they all mean different things, hence why 'nice' is not a great word to use.
People often use 'temperate' which is a much more specific word relating to climate and means "a region or climate characterized by mild temperatures".