Can the weather (i.e. winter vs. summer) affect the severity of copd?

No: But it has been observed that COPD flare ups are more common in winter and this is more related to increased chances of pneumonia and flu. Some people with COPD also have allergies that flare in spring and/or fall.

Yes: I have definitely seen different patients do worse at different times of the year. Definitely, more people with COPD can get into trouble in the winter: it could be either from cold air, or the many respiratory viruses (like the flu) which are in season. But, at the same time, some of my patients with COPD do worse with the very humid weather of the summer. But, typically, winter is worse.