I know for sure that the spring season, early April through mid-May, is usually when I get hit the hardest. From the very first dx in April to several acute attacks in and around this time frame. I always kind of thought it had something to do with allergies?
But also, some of the worst episodes I've had were after exposure to high heat in the summer months.
So yes, I do believe that the season changes has some impact on the activity of MS - at least in my opinion.
But now with the discovery of CCSVI, this is probably no longer valid!! Perhaps the change of season has some influence on blood pressure, flow, density or what ever? I don't know, but I do know that I pay a lot more attention in the spring (for whatever that's worth).