TIPS on Photographing Snow:
If most of the image is white, the meter will be fooled and
UNDEREXPOSE the negative making your photo gray.
If you know how to use exposure compensation or manual control, you change your settings to
add more brightness to the image by overexposing one or two "stops".
If your camera has a needle or red/green indicators, just have it go into the plus side.
If you have an exposure compensation feature- set it to plus one or two.

A safe and easy way for proper exposure is to meter a "gray card" or any middle gray subject matter in the same light as your subject. Use the reading from the gray card when you re-compose on your subject.

When unsure, many photographers "bracket" their exposures by
shooting a variety of exposures of the same subject at different settings.

Strong sunlight can also play tricks with the meter and exaggerate the
effect of the white subject. If the scene seems to average out lights
and darks, you can trust your meter. Sometimes strong light creates
shadows that make the snow look darker in some areas and it all
averages out.