Yes. It's based on an old story... Essentially there were two lovers that were separated for whatever reason... There are a few versions. They were granted one day of the year to be together, but they could only see each other if the weather was good since they have to cross a river...

Ahh, but I'm about to ramble on too much. The story is retold in the sky through the stars, and traditionally people would ask for good weather to cheer them on.