Complex sentence: In the United Kingdom, July 15 is known as St. Swithun's day; it was traditionally believed that, if it rained on that day, it would rain for the next 40 days and nights.
Split into simpler sentences: In the United Kingdom, July 15 is known as St Swithun's day. It was traditionally believed that, if it rained on that day, it would rain for the next 40 days and nights.