Remeber, an incident meter is going to measure the light falling on the snow for 18%. So, use that meter and set your camera to that and, BAM you're whites are white. Now, spot meter is going to give you 18% reflection off the snow. So measure the snow, that will make all your snow gray, over expose 1stop and you'll have 36%, +2 72%, +3 and you'll have 144%, which will be blown. That theory being said, I would use the incient meter when possible and, and still underexpose just to be safe on the whites. As we all know, when reversal film blows whites, they are gone. Besides, underexposing slides will give you a very nice, saturated chrome.
I hope that helps. All those years of photo school should have taught me something.
Enjoy the Alps.
-Brandon