Beware the Ice Saints.

Beware the days of the Ice Saints, St Marmertus (11th May), St Pancras (12th May), St Serviatus (13th May, St Boneface (14th May). In many parts of Europe these days are feared as there is often a sudden sharp frost after warm weather that can catch the vines and ruin the grape harvest.

The Ice Lady or Cold Sophia, St Sophia (15th May) is also included in some countries

Worrying is the fact that these saints days were fixed on the Julian calendar. When this changed to the Gregorian calendar there were 10 extra days put in so the Ice Saints should really be May 21st to 25th.