St Swithun's day if thou dost rain

For forty days it will remain

St Swithun's day if thou be fair

For forty days 'twill rain nae mare

Groundhog Day is perhaps the best known of the ‘weather predicting’ celebrations, if only because of Bill Murray’s purgatorial experiences in the classic rom-com. However, St. Swithin’s Day (or Swithun’s, a name sometimes said to mean the flattering 'pig man') is an English feast day that is said to be another indicator of forthcoming seasonal fortunes, and one more likely to affect us here in Ireland than the Pennsylvanian groundhogs.

It is said that if it rains on July 15th, the rest of July and most of August are going to be equally miserable. Of course, such a customary belief should be taken with several spoonfuls of salt in these more sceptical times of ours. However, it’s hard to not be a little concerned looking up at those grey clouds that have fairly definitively brought over a week of finest sunshine to a close.

Swithin was a 9th century Bishop of Winchester - posthumously promoted to the patron saint of the same diocese following several alleged miracles (including reportedly ‘fixing’ a basket of cracked eggs). Swithin’s, who died in 862, was known as a popular spiritual leader who would, among other compassionate activities, celebrate banquets with the poor rather than the rich.

Origins of a myth

So: how exactly did Swithin become associated with superstitious weather prediction? Opinions differ wildly, to say the least. One theory proposes the myth originated in 971, with an attempt to move Smithin’s remains to a new shrine, but a violent rainstorm signaled the saint’s displeasure at the move.

Other observers suggest the St. Swithin’s Day myth is a re-appropriation of pagan beliefs, particularly similar to some originating in Gallic territories. St Gervais Day, celebrated in France on July 19th, offers an identical prediction of forty days of rain.

However, there have actually been meteorological explanations proposed for why rain on July 15th may signal a trend. Summer weather for the British Isles are heavily dictated by a jet stream and ‘frontal zone’, with the weather for early-mid July likely to give a decent indication of the weather to follow for the next month or two. If the jet stream brings cool, unsettled air with it, then British and Irish observers can, with a not insignificant degree of accuracy, expect 40 days of cool, unsettled weather.

July 15th might not be any better a medium-term weather indicator than July 14th or 16th. Obviously it's incredibly unlikely we'll ever get 40 consecutive days of identical weather given the countless factors that determine sun, rain, temperatures and clouds. But the Swithin’s Day tale is at least grounded in some sort of general meteorological reality, even if the old wives may not have been consciously aware of it.