Actually, if you do regular weight lifting exercise with your fistula arm, there's no reason shoveling should hurt it. Ask Zach and Bill Peckham- they both lift weights regularly with their fistulas and don't have a problem. I remember reading one post where Bill was talking about doing chin-ups.
Sorry to hear about the problems that snow brings. According to press reports it got even worse over the last couple of days. BTW, I have just realized that my American friends work in Fahrenheit so 42 degrees is in fact 108 degrees F. That is hot.