Getting a correct exposure outdoors in snow can be challenging. Remember that the meter is trying to make the value of the scene 50% grey, whether it is looking at a pure white scene or a pure black scene. Try shooting a white card and a black card in any of the auto modes to prove this to yourself.
What that means, then, is that if you are shooting a snow scene, you have to increase the exposure so instead of the snow being grey, it comes out close to white. One way to make the correction is by using the exposure compensation feature of your camera, and adding about 2 stops of exposure to make the scene work. Check your histogram to make sure you haven't lost detail.
The photograph shown here was taken in Rocky Mountain National Park, about 65 miles north of Denver.
For a more detailed explanation on this, with more examples, and other photography tips, check out my blog at http://www.abetterphotograph.com.