weathering a sherman

There are a lot of ways and they all work. You can drybrush white over the base color, or drybrush the base color over white. You can use railroad model scenic snow, or you can simulate whitewash like the recent FSM article, with powdered white chalk pastel and water. It depends on whether you are trying to simulate a worn winter camouflage, or whether you want the tank to look like there is snow on it.

I agree...the question is a little vague.....do you want it to look like a winter paint scheme or look like actual snow? If it is snow that you want, then I would suggest baking soda. It looks perfect. Every little piece glimmers just like real snow.