Okay, I lost a few of you--don't worry. The camera sees all the light bouncing off the snow and wants to make the photo quickly--thus the grey snow. If you see that and your camera has an exposure compensation adjustment, use that to manually add in +1 stop of time. This gives the camera a little more time, and thus light, to make the photo and the snow becomes whiter.
Also, don't be afraid to use your flash outside on those bright snow days. If your subject is near the snow's bright service their face may look perfect. If you have them in a shadow, turned away from the bright snow, or the day is cloudy, use the flash to "fill-in" the face for a printable image!