As stated in the title, I think it would be really interesting if the Copper Barometer's dial could change over time. For instance if it's clear and it starts to approach a storm, the dial could lower, indicating the pressure is dropping until it drops to a certain amount, which then the storm that it's predicting would start. Perhaps even thunderstorms could drop lower than rain on the barometer since they could have lower air pressure. Then when thunder or rain ends, it could rise back up again.

I think this would be a neat little visual addition that fits in well with the base game since clocks and compasses already do something similar to this, plus it would allow players to put barometers in item frames, allowing them to be still functional, even if you aren't holding it.