I ski all winter myself (Alpine and Nordic).  I have found that inline skating and roller skiing in the summer keeps me best prepared for the winter.  Easy to do around the neighborhood for as short or long as possible.  Use a headlamp and head out after the kids are in bed if need be.  Use a stationary bike or treadmill for the bad weather days.  Nothing like inline will keep you as prepared for alpine ski season in terms of muscles used, balance, etc.  It is practically the same motion as alpine, plus even moderate hills on inline skates can be fun/challenging.  Rollerblade even has a free skate to ski training guide.  I prefer a 90-100 MM wheel diameter with 84-88 durometer and a soft boot for inline skates, use manufacturers recommendation for roller skis.  Rigid boots are more like alpine ski boots, but the soft boots have enough support that comfort/breath-ability outweighs in this regard.  Use with or without poles, but be sure to get special tips for pavement if you do use them.  If you want to go real extreme there are even offload pneumatic inline skates for the trails, but they have a very steep learning curve.

I also agree with the other posters that cardio is key for ski season and add some leg weight exercises if you can.

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