Your metering mode could also affect how bright it comes out.
AV (aperture mode) is a semi-automatic mode, so when the camera sees lots of bright white snow it might say “whoa! too much light!” and bump up your shutter speed or bump down the iso to avoid having bring white patches in the picture. Of course, snow is bright and white, but the camera may not know that. It is only so smart, after all. 🙂