St Swithin's Day: Weather legend may be closer to the truth than you realise

'St Swithun's day if thou dost rain, For forty days it will remain.' Or will it?

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Today is 15 July - St Swithin's Day. Legend has it that if it rains on St Swithin's Day then the wet weather will continue for 40 days.

What's the proverb again?

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

And who was St Swithin?

He was a cleric in 9th-century Wessex, the bishop of Winchester and later patron saint of Winchester Cathedral.

Born around 800, he became an adviser to Anglo-Saxon Kings Egbert and Aethelwulf and later a mentor to the young future King Alfred.

What's with the link to the weather?

St Swithin only came to be venerated some time after his death in around 862.

His dying wish was that he be buried - unlike previous bishops - outside Winchester Cathedral, "where the sweet rain of heaven may fall upon my grave".

But, the story goes, this was overruled by his reform-minded successor, Aethelwold, who in 971 arranged for St Swithin's remains to a more fitting, opulent shrine inside the cathedral and made his predecessor patron saint.

But the ceremony, on 15 July, was ruined by a huge downpour, breaking a period of drought, with the rain continuing for weeks afterwards.

Whether this actually happened on the precise date of the legend is a matter of historical debate - and different parts of St Swithin's remains have been moved to different shrines since then.

When did people start to recognise the legend?

There is a long, proud tradition of supposedly weather-forecasting days dating back as far as pagan, Roman or even prehistoric times and many countries celebrate a similar day, usually nominated after other saints.

The earliest legends to the St Swithin's Day legend date back to the 14th century, and may only have started to become really popular in the 17th and 18th centuries.

And surely the legend is just that - an old wives' tale?

According to the Met Office, there is precisely no evidence that the weather on 15 July is a good way to predict the weather over the next 40 days and nights, up to 23 August.

But there's a grain of truth in it, as weather often locks into a pattern in high summer, only changing when autumn begins to rear its head from the end of August.

So, what's the weather going to be like this year?

The forecast for today, 15 July 2015, is for a mixture of sunshine and showers. And this mixed picture is set to continue for the foreseeable future, with warm sunshine punctuated by storms and showers. In other words, pretty much like every other British summer.