Saints de Glace (Icy Saints) used to be a catholic tradition which happens every year on May 11th,12th and 13th.
According to the previous Catholic calendar it was St. Mamert (on the 11th), St Pancrace (on the 12th) and St Servais (on the 13th) they have now been replaced by St Estelle, Achille and Rolande.
In 470, after realizing that a few climatic disasters at this time of the year happened every year, St Marmert decided to pray during those 3 days to protect the work of the farmers.
Of course, most of the time it did not stop climatic damages, but those days stayed famous for their bad weather (raining, drop of temperature, morning freezing).
Apparently, something to do with the April moon, but we are not sure, but according to weather specialists the "Icy Saints" are now around May 20th.
It can freeze up to May 25th but after that the gardeners can put everything in the garden and summer is starting!
Not sure if you believe in it or not but if you do not want a rainy holiday in Annecy have a look at the weather forecast!