Recently, our toddler's pre-school held a "Snow Day." They brought in a snow making machine to make a bit of snow and a slide. It was fun to watch the kids' expressions as they played with the 'snow'. (My apologies to people in parts of the country that are freezing...)
Although I brought a flash with me and was planning to use it to put a spotlight on our toddler (to separate him from the other toddlers), I decided not to use it because the ambient conditions were too good to improve upon. The snow was reflecting the light from the sky nicely and put a soft light on our toddler. If I had used the flash, it would likely have overpowered the soft light from the snow and looked artificial.
I was also expecting some metering problems, thinking that the snow would be rendered gray by the camera's automatic exposure (I was on aperture priority mode most of the time to try to isolate the intended subject -- our toddler). But the snow didn't fool the camera this time and was rendered white (except for shadowed areas), just short of blowing them out. At that exposure, the surrounding walls looked kind of gray, so I brightened them selectively during postprocessing to get a high-key look.