St Swithin's Day if thou dost rain
For forty days it will remain
St Swithin's Day if thou be fair
For forty days 'twill rain nae mare
Today, 15th July is St Swithin's Day. A day when weather watchers in the UK take note for, as the above folk lore rhyme claims, whatever the weather does today will continue in this fashion for the next forty days.
The legend is an old one, with the earliest surviving references dating back to the 14th century, though the sources are somewhat disputed. St Swithin (or Swithun as it is more properly recalled) was a Saxon bishop of Winchester having been consecrated as such in either October 852 or 853. He was said to be an apple grower and renowned for building places of worship and providing charitable donations. He remained in the position of bishop until his death in the summer month of July sometime between 826 and 865. Upon his death his wish was to be buried outdoors, away from the church crypt and tombs, to be interred with the common people and his parishioners where he would be walked and rained upon. The legend is largely believed to have stemmed from his elevation to patron saint of Winchester Cathedral in 971, which saw his body being dug up from the common ground to be placed inside the church in a newly constructed shrine. Going against Swithun's wishes - however kindly intended - incurred the saint's displeasure and a terrible downpour fell upon the cathedral and surrounding environs for a full 40 days.
It's not just the UK where such folklore exists either, in France they have Saint Medard on the 8th June and Saint Gervase and Saint Protais on the 19th June. Likewise in Flanders there is Saint Godelieve on the 6th July whilst on 27th June in Germany there is Seven Sleepers Day. All of these dates are believed to influence the forthcoming weather in the same manner we believe St Swithin's to be, which suggests a more common Pagan influence to the myth.
Whatever the real origins St Swithun remains part of our heritage and is one of the patron saints Christians pray to in times of drought. He is also the saint whom apple growers ask for blessing each year for they believe that rain on St Swithin's Day blesses and christens the apples, that no apple should be picked or eaten before 15th July and that apples still growing on that day will not ripen.
It's certainly an intriguing bit of folklore but there's no real evidence for it having actually happened. Whilst the Met Office have since tested rainfall on St Swithin's Day a total of 55 times and there has been no record of continuous downpour in a period of forty days following.
However, the Met Office do believe there is something to the old wives tale. The middle of July (which is when the saint's day falls) tends to be the period of time when the jet stream settles into a relatively consistent pattern. If the jet stream lies north of the UK throughout the summer, continental high pressure is able to move in, bringing warmth and sunshine. If it sticks further south, it is the Arctic and/or Atlantic air and weather systems which are likely to figure, bringing colder, wetter weathers.