(First published in Where to Ski and Snowboard 2012)
Altitude, of course, affects the likelihood of rain, but geographical location is also key.
Rain at altitude in winter is almost always associated with warm fronts - advancing boundaries between a warm air mass and a cold air mass. These generally arrive from the west and mostly affect the northern Alps - so the north-western Alps are most at risk. Here rain has been known to reach 2700m (even in mid-winter) so high resorts such as Courchevel and Val d'Isère are not completely immune. However, it is obviously the lower resorts of the north-western Alps that are most vulnerable including Morzine and Megève in France and Villars and Wengen in Switzerland.
The risk of rain quickly drops as you move south and east. As you go south, you get fewer warm fronts. As you go east, the effect of the fronts is reduced. In the heart of the Alps, in valleys sheltered from westerly winds, cold air gets trapped in, while advancing warmer air rides over the top. You can get rain over 2000m in Chamonix, on one side of Mont Blanc, while it is snowing at 1200m in Courmayeur, on the other side.