I will tell you Humidity does not help my myotonia but for sure cold weather does make it much worse. So in general I would say my myotonia is "normal" when the weather is okay or hot but worse when its cold. Cold meaning anything below 40 degrees.
From my observation these are the scenarios where my myotonia gets worse:
Cold Weather
When I'm hungry
When I sleep too much
Social situations where I feel my myotonia will be exposed
I can't unstiffen if it's too cold, so no. Even a chilly morning is bad.
If it's too hot, though, I'm working so very hard that I can overheat more easily than other people. So that's bad, too. My muscles are just doing more work for the same result.