July 15th is St. Swithun’s Day, and according to old British lore, if it rains on that day, it will rain for the next 40 days. We know this is true because a poem says so:
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.
Makes about as much sense as waiting for an overgrown weasel to see its shadow.
Swithun was Bishop of Winchester in the 9th century, and much of what we know of him comes from later hagiography. His fame came about a century after his death, when his remains were transferred from an outdoor grave (where he wished to be buried so people could walk over his resting place) to Winchester Cathedral. This is supposed to have irritated the Saint, who made the day of the transfer of his relics (his current feast day: July 15th) notoriously rainy, and it remained so ever after.
In fact, Swithun is not alone in the power of weather forecasting at this time of the year. In June and July, St. Medard (France), The Seven Sleepers (Germany), and St. Godelieve (Flanders) are attached to similar lore in places, which may in fact originate in in pre-Christian times: a kind of a pagan Farmer’s Almanac. It’s not that far-fetched. Weather can fall into patterns in July that last through August.
The saint also got attached to the phrase “from now until St. Swithun’s day” to indicate a really long time. Or maybe it was just something Col. Potter said on MASH.