Use exposure compensation to add light.
It’s currently 18 °F as I write this on the 13th day of November. The projected high temp for today is a meager 28° so Sunday’s snow is not leaving soon ( or soon enough). Why not, I thought, get out with a camera so I took a trip to one of the local forest preserves for snow shots. The camera’s only goal in life is to even out the light level in any scene so I had to be vary aware of possible under-exposure since there was an enormous amount of light in the scene. In this case, I used the exposure compensation setting on the camera to add a full stop of light (e/v +1) to keep the snow white. If your camera doesn’t have exposure compensation (in either a menu setting or a button) and you’re concerned about keeping snow white, ask a dwarf.
For you camera setting bugs here’s what I used for this shot: 180mm lens, f8 @ 125, e/v +1, ISO 125, center-weighted metering pattern, WB: Sun.