How good of exercise is skiing?
How many calories can you burn?
What major muscle groups are you using?
Is it low or high impact? (Maybe that depends on falling.)
For an intermediate to advanced skiing.
Tags: high impact, how many calories, major muscle groups, skiing

Your calories per hour will vary for each individual because of height, weight, BMI, and metabolic rate. You can get a ballpark idea from this website: http://www.soft4everyone.com/tools_activity_calorie_counter.php
Quads, Gluets, Groin, and Hamstrings are the major ones. Your core and back will get a workout as well. A backcountry skier traversing terrain, a mogul, or terrain park skier can expect to use more muscle groups than a casual skier.
Cruising around is relatively low impact. Skiing moguls and terrain park has a significant amount of impact. While falling could lead to an impact related injury, it’s not the same type of impact injury sustained by repetitive motion such as running.