It's not a complicated song, it's basically a clever way of combining weather forecasting terminology with emotional description.
Crying is equated with precipitation and rain, clouds and fog related to confusion and a 'foggy' state of mind, in other words uncertainty in dealing with a bad breakup, and how to continue in a healthy way. What follows is predictable to a degree, like weather, but it's not exactly going to be sunny for Tom here.
It's not a complicated song, it's basically a clever way of combining weather forecasting terminology with emotional description. Crying is equated with precipitation and rain, clouds and fog related to confusion and a 'foggy' state of mind, in other words uncertainty in dealing with a bad breakup, and how to continue in a healthy way. What follows is predictable to a degree, like weather, but it's not exactly going to be sunny for Tom here.