This is the real key to good skiing pictures. All too often you're shooting in extremely bright conditions. The snow is very bright. So is the sky. And your built-in meter interprets all this brightness to mean that you don't need much exposure.
Most pictures taken on the slopes are underexposed.
Sure, the snow looks great. And so does the sky. So, try taking a closeup reading of the skier's face, and set your exposure accordingly. Use that exposure setting when you later take the shot. Another option is to use fill flash.