Almost snow-sure, but Avoriaz just misses the site's threshold (25 snowy Christmases out of 30): at mid-mountain, 1,700 m, there was enough natural snow over the holidays in 23 winters of 1984/85–2013/14. With snowmaking it comes out at 30 of 30. The trend here is unusual: all seven snowless Christmases fell within 1984/85–2001/02, and in the last 12 winters of the series there were no misses. Splitting the series in half, that's 10 of 15 and 13 of 15. This is a record of past winters, not a forecast: models for 2041–2060 (RCP4.5) give 7.1 Christmas days with snow out of 14 against 9.4 in the model reference 1986–2005 (methodology).
Snow in April and on the lower runs
In a typical winter, continuous natural snow cover holds from 10 December to 28 April, so an April trip to Portes du Soleil is worthwhile. Down low it's a different story: the lowest run at 1,156 m was snowy in 6 of 30 Christmases, while the highest run at 2,250 m was in all 30. At neighbouring Les Gets - Morzine, at 1,500 m, it comes out at 20 of 30. At Christmas Avoriaz is more reliable than its neighbour, but the safest bet here is January to April.