abrupt and inconsistent. How can the sun come out after a heavy rain? Why is the milkman wearing a hat and coat in summer time? If you want to end your story with a happy note, you could write something like this:
They drove back home in the rain, feeling happy and content. They didn’t mind getting wet, because they had had a wonderful birthday celebration with their friends. They were looking forward to seeing them again soon. As they reached their house, they saw a rainbow in the sky. It was a beautiful sight. They smiled and thanked the sky for giving them such a lovely gift.