In cold weather, your body still sweats. And sweaty clothing in cold weather is not a good thing. The job of your next-to-skin or base layer is to wick moisture. 

Look for synthetic materials such as polyester shirts or long underwear. If you prefer a natural fabric, choose wool or silk. Always avoid 100% cotton base layer which absorbs sweat and holds it close to your skin.

As you shop, you may notice that some shells are "waterproof" and some are "water-resistant." All have outer surfaces that are treated with a DWR or durable water-resistant finish which helps shed water so it's not absorbed by the fabric. 

Also have a coating or laminate on the inside of the garment, and the seams are sealed so you stay dry from the inside out as well as from the outside in. Bottom-line, water-resistant outerwear is fine in mild weather, but prolonged wetness needs a waterproof jacket or pant.

Using layers gives you options you can customize your clothing, just like you customized your deck. This versatility means a better value too, allowing your outerwear set to adapt from mild autumns to chilly winters to rainy springs.

So layer up, and make the most of your new gear! If the day starts out cold and it's bluebird by noon, take off one of the base layers and open those vents to enjoy the sun. Have fun, and enjoy the mountain life.