St. Swithun's Day
St. Swithun, Bishop of Winchester, was born around the year 800 and died on 2nd of July 862 at Winchester (Hampshire). He was, say the chroniclers, a diligent builder of churches in places where there were none before and a repairer of those that had been destroyed or ruined. St. Swithun was buried, according to his own desire, in the churchyard of the Old Minster (Cathedral) at Winchester, where passers by might tread on his grave and where the rain from the eaves might fall on it.
His reputation as a weather saint is said to have arisen from the translation of his body from this lowly grave to its golden shrine within the Cathedral, having been delayed by incessant rain.
The meteorological interpretation is quite straightforward. The position of the frontal zone around the end of June to early July, indicated by the position of the jet stream, determines the general weather patterns (hot, cold, dry, wet) for the rest of the summer. Like a little stream in its bed, the frontal zone tends to 'dig in' shortly after the summer solstice.
Try and prepare your own summer forecast with our expert maps. The 500mbar maps usually give a good idea about the position of the frontal zone. Have a look at them over the next two weeks and produce a DIY summer forecast valid until mid-August with a confidence of 70 to 80%.
No wonder the St. Swithun's day rule is also know in other western European countries. In France they say Quand il pleut a la Saint Gervais Il pleut quarante jours apres - If it rains on St. Gervais' day (19th of July), it will rain for fourty days thereafter.