If it rains on St Swithin’s Day it will rain for the next 40 days. If St Swithin’s Day is dry, the next 40 days will also be dry.
A particularly English fallacy is the idea that if it rains on 15 July, St Swithin’s Day, it will rain for the subsequent forty days.
We aren’t normally blessed with a decent summer in the UK and our topsy-turvy weather makes prolonged rainfall likely but even forty days is stretching it a bit.
The myth started in AD 971 when on the 15 July the monks of the cathedral at Winchester decided to remove the remains of St Swithin from the churchyard and re-inter them inside the cathedral.
Swithin, or more accurately Swithun, was the Bishop of Winchester and unlike other religious figures, he asked not to be buried in a prominent place within Winchester Cathedral, but outside in a simple tomb “where the sweet rain of heaven may fall upon my grave”. It was also where his grave could easily be reached by members of the parish.
The monks were having none of it and their sacrilegious act was followed, apparently, by forty days of continuous rain suggesting St Swithun was not very happy with his new resting place.
As we don’t have any meterological records from this time then no one can say for sure what the precipitation levels were like but that doesn’t stop some people still clinging to the fallacy of St Swithin.
There is a well-known rhyme which keeps the superstition going:
St Swithin’s Day, if it does rain
Full forty days, it will remain
St Swithin’s Day, if it be fair
For forty days, t’will rain no more
Since records began in 1861, there has never been a record of 40 dry or 40 wet days in a row following St Swithin’s Day.
St Swithin’s Day is nothing more than folklore.
For more information then see Philip Ward’s The Book of Common Fallacies: Falsehoods, Misconceptions, Flawed Facts, and Half-Truths That Are Ruining Your Life.