According to folklore, if it rains on the saint's day, it will also rain for the following 40 days.
The myth also works the other way round - if we have fine weather, it's also supposed to be repeated for the next 40 days.
St Swithin - his name is sometimes spelled as Swithun - was an Anglo-Saxon bishop of Winchester Cathedral, then the capital of the ancient kingdom of Wessex. He died in 862. He was a close confidante of the West Saxon king, Egbert.
He is credited with performing a miracle when he repaired an old lady's smashed eggs, which had been damaged by men while building a church.
The weather-related suspicion derives from his humble request to be buried outside the cathedral's Old Minster, where his grave would be rained on.
Yet later generations of monks defied his last wishes, and removed his remains to a far less modest shrine inside the cathedral, claiming his bones had healing properties, before opening it to the public.
The saint's spirit expressed its displeasure at the desecration through an series of unrelenting rainstorms, which occurred both on the day of his exhumation and for the next 40 days and nights.
And the weather forecast for Yorkshire tomorrow does predict some rain showers on Saturday morning - before a settled week which could see temperatures reach 22 degrees.