Happens all the time here...

But any time of the year it"s very dry, it is common for a mower blade to hit a rock and cause a spark which ignites dry grass...happens every late summer somewhere in our region during haymaking. You see it on our local news two, three times a year.

I don"t see why a plow blade couldn"t do the same thing under the right circumstances, although it"s much less likely. A mower blade has so much more velocity. But then, the plow blade hits more rocks...

But I"ve also seen sparks fly from old tractor and lawn mower mufflers after dark. These wouldn"t have much heat in them, although their temperature is high enough to make them incandescent. I"ve got to think they"d still be more likely to start a fire than a spark thrown from a plow.