St. swithin's day

From Glossary of Meteorology

St. Swithin's Day

In English folklore, a day that is popularly supposed to govern the weather of the succeeding 40 days; specifically, if it rains on St. Swithin's Day, 15 July, it will continue to rain for 40 days.

Not even a tendency toward this is borne out by weather records. Similar legends relate to other saints' days in many countries.
See control day.

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