Ice Saints

[1] In parts of the Northern Hemisphere, the period from May 12 to May 15 is often believed to bring a brief spell of colder weather in many years, including the last nightly frosts of the spring.

Pupils of Galileo confirmed this weather pattern for the years 1655-70 and reported a marked cold snap over the days of the Ice Saints.

However, in 1902 William Dines, President of the Royal Meteorological Society, used modern statistical techniques to demonstrate that the Ice Saints were a myth, brought about by selective reporting.

[4] In southern Germany, many gardeners don't plant until the end of the "Eisheilige," the four successive feast days of the "ice saints" Mamertus, Pancras, Servatus and Boniface — May 11-14.

In Sweden, the German legend of the Ice Saints has resulted in the belief that there are special "järnnätter" (Swedish for "iron nights") especially in early June, which are susceptible to frost.