What to wear/Lockers
Dressing in layers is key. During the day when the sun is out and your dancing it can get pretty warm but as the weather high up in the mountains can literally change within minutes from sunny and warm to a snowstorm it´s always nice to be able to adapt to the changing conditions.
The indoor stages at the main festival area are heated, hence it makes sense to change to some lighter clothing after you´ve been out skiing during the day. There is a limited amount of lockers available at the festival area which can be booked in the add-on sale. However, you can also leave your parka and your skiing pants at your hotel or apartment and wear something light and comfy when you´re heading to the festival at night. It might be a bit chilly on the walk to the stages and back to your lodging but carrying loads of jackets around all night isn´t nice and piling them up and dancing around them is not a good idea either. Also it will give you some angry looks from other festival goers which have less space to dance.
That said, be prepared for cold temperatures in general. Alpe d´Huez is at an altitude of 1800 metres with the skiing area reaching its peak at 3300 metres. It´s not unusual that temperatures drop to -15 or -20 degree Celsius at night. Expect day temperatures around 0 to 5 degree Celsius on sunny days but be prepared for them to drop in case it´s snowing all week long.