St Swithin’s Day was wet for much of the UK yesterday as showers swept through before the sun shone. And according to the folklore saying that means we can expect 40 more days of rain:

St. Swithin’s day, if ye do rain,

For forty days it will remain;

St. Swithin’s day, if ye be fair,

For forty days ‘twill rain nae mair.

St Swithin was a 9th-century bishop of Winchester who insisted that his remains be buried outside under all weathers. But years later his body was moved inside the cathedral, and on that day a tempest supposedly broke out followed by 40 days of rain. From then on July 15 became cursed with St Swithin’s prediction, but it never strictly comes true. However, some years have been a close run thing, such as the hot summer of 1976, when 38 out of 40 days were dry following St Swithin’s Day.

There is a grain of truth to the folklore, though, because the weather around mid-July often gets stuck in a rut. “July and August is the time when there is a noticeable tendency for the weather to get into a particular mode and persist — it’s the general weather for a couple of weeks around St Swithin’s Day that matters, not the day itself,” says Chris Folland, at the Met Office Hadley Centre.

So, a better version of St Swithin’s saying might go: If it rains a lot in the fortnight around July 15, expect unsettled weather for the rest of the summer, but if it’s fair, then decent weather is on the way. Not as catchy, but closer to the truth.