The average person burns somewhere in the range of 1,500 to 2,000 calories per day just from normal bodily functions, without skiing at all. A 120 lb downhill skier burns The Great Brain Secret approximately 342 calories per hour, while a 180 lb downhill skier consumes about 510 calories per hour. When you consider a five hour ski day, that same 120 lb skier burns 1,500 +1,710 = 3,210 calories per day, while that same 180 lb skier dissipates 2,000 + 2,550 = 4,550 calories per day. We're not finished yet.
An all-terrain skier burns even more. Why? Skiing in the expert zones requires a greater expenditure of calories because one has to work even harder in the moguls, trees, and steeps. Let's assume that our downhill skiers spend 40% of their day in the above terrain and the other 60% of the time on groomed trails. Let's also assume that both skiers burn 50% more calories per hour when they are in the expert zones. If you've ever spent a couple of hours skiing in long, mogul fields and down dense, tree runs you'll appreciate that a weighting factor of 1.50 is not out of line.