It looks like it has a method called
Not sure how you are implimenting it but it should be something like
<button onclick = "snowStorm().freeze()">
You could even do something a little more intuitive on the lines of
<button onclick = "ToggleSnowStorm()"/>
Obviously the code may not be exact since I don't see your page but this should give you an idea of where to start.
If you look into cookies you could probably use a cookie to see if the user prefers it toggled on or off if you expect to have return visitors.