Is it a bad sentence that the weather is changing?

No.

1. Weather is a noun, which means weather changes in a small area.

2. Changes in wind and clouds: Wind and clouds: a metaphor for changing and turbulent situations; change: changes are uncertain. Describes the changeable weather. Present metaphor is that the situation is complex; it changes rapidly; it is unpredictable. There is no conflict in interpretation, and there is no grammatical problem that causes the sentences to not make sense.