The weather was really bad. We couldn’t go sightseeing as planned. A. If the weather weren’t really bad, we could go sightseeing as planned. B. Unless the weather is bad, we can go sightsee

If the weather weren’t really bad, we could go sightseeing as planned.

Unless the weather is bad, we can go sightseeing as planned.

But for the bad weather, we could have gone sightseeing as planned.

Provided that the weather isn’t bad, we can’t go sightseeing as planned.