I’ve always noticed that cold weather has an effect on my breathing. It can almost make me feel like i’m short of breath. And after looking it up, that’s exactly what happens to most people. For people who stutter, anything that disrupts breathing will most likely making your stutter worse. That’s why when I get excited or out of breath from exercising, it’s always the worst. I have noticed that running and improving cardio and lung stamina and capacity has helped me tremendously. Not sure the severity of your stutter, but if you’re not active and in shape, could be worth a try.