The following are both estimates as it depends how much you weigh and how hard you work, etc.
Thirty minutes of snowboarding burns about 330 calories, so it's an excellent way of increasing your calorie expenditure, which will help you to reduce weight.
This calorie-burning is based on a 150-pound woman. So if you weigh more, you'll burn extra calories, while if you weigh a little less, you'll burn less calories.
Downhill skiing for a 160 pound person burns around 365 calories.