Snow exposure compensation

[swoosta]

"When you take a picture in snow you may have to overexpose by a couple on stops."
Can someone explain this to me I thought it would be the other way round as the snow would over expose the reading?

[flake]

Put simply the cameras auto exposure system looks to make a scene 18% grey. When a scene is virtually all white the camera still tries to make the scene 18% grey so to acheive this it underexposes and makes the snow darker than it should be, the extra stop or two brings the exposure back to where it should be.

[swoosta]

Thanks for explaining
cheers