Skiing is meant to be Type I fun, which means you can and should be comfortable on the slopes in all but the most extreme weather. The key to staying warm and dry lies in your layering system, which is generally made up of a next-to-skin base layer, an insulated midlayer, and a ski jacket. Knowing how to fine-tune these layers to the conditions will take some trial and error based on the individual (whether you run cold or warm, for instance) and the specific layers you have in your closet.