Look on the snowheads forum. There's a thread there called the view from val disere. In the weather reports section. Steve who lives out there updates it most days with photos. I was glued to it last year.
But I'd have thought it would be fine, it's high up and e space Killy have excellent piste bashers, artificial snow cannons, etc if needed.
We were in Val D'Isere last week (linked to Tignes). The snow conditions are fabulous, they have far better snow cover than usual for this time of year. I think it snowed a lot before Christmas and over Christmas week and there was a further fall of 2 or 3 inches last week. Even if it doesn't snow at all between now and half term it should be fine in Tignes then.