Digital cameras shoot in grey values and for most situations this is great. But when you are shooting at the extreme tonal ranges such as white snow your camera meters that whiteness as neutral 18% grey to compensate for the lack of contrast. There are a couple ways to get around this. The first one is simple for some, many camera manufactures have a snow setting in the automatic dial that makes the necessary compensations. But not everyone has this option.
The next step and most effective solution is to shoot manual. By doing so you can move your settings to slightly overexpose the image. A half to a full stop over for cloud cover, and one to two stops for sun will bring that scene back to white. Be careful not to go too far. You don't want areas that are completely washed out.
If your are in doubt about how bright your photo is, you can always look at the histogram. What is that you ask? When viewing your photo on the LCD screen most cameras have an info or display button. This brings up a graph that often looks like a mountain. When you are shooting snow the graph information will be mostly over to the right. What you want to avoid is that information going completely off the right side. This means your photo is severely overexposed and there is no way to fix it later. If the majority of the information is to the right but not going off the edge chances are you will have white snow, but histograms that show all the information in the middle, in this situation, will render that grey snow that you are trying to avoid.
Snow is fun to shoot but to get the results that you are seeking you must trick your camera meter in order to get that 'white as snow' appearance. Happy shooting while the snow last, spring is just around the corner.