The Ice Saints take place from May 11, 2021 till May 15, 2021. The Ice Saints is a name given to St. Mamertus, St. Pancras, and St. Servatius in folklore of some Europe countries. They are so named because their feast days fall on the days of May 11, May 12, and May 13 respectively.
The period from May 12 to May 15 was noted to bring a brief spell of colder weather in many years, including the last nightly frosts of the spring, in the Northern Hemisphere under the Julian Calendar. The introduction of the Gregorian Calendar in 1582 involved skipping 10 days in the calendar, so that the equivalent days from the climatic point of view became May 22 - 25. (With material from: Wikipedia)