The local Feast on the 15th. July, here in the Archdiocese of Southwark, England, is that of St. Swithun, Bishop of Winchester.
The following are taken from Wikipaedia:
"Swithun (or Swithin, Old English: Swīþhūn, Latin: Swithunus; died c. 862 A.D.) was an Anglo-Saxon bishop of Winchester and subsequently patron saint of Winchester Cathedral. His historical importance as bishop is overshadowed by his reputation for posthumous miracle-working. According to tradition, the weather on his feast day (15 July) will continue for forty days. The precise meaning and origin of Swithun's name is unknown, but it most likely derives from the Old English word swiþ, 'strong'."
"The name of Swithun is best known today for a British weather lore proverb, which says that if it rains on Saint Swithun's day, 15 July, it will rain for 40 days.
- 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
- If on St Swithun's day it really pours
- You're better off to stay indoors.
In 971 it was decided to move his body to a new indoor shrine, and one theory traces the origin of the legend to a heavy shower by which, on the day of the move, the saint marked his displeasure towards those who were removing his remains. This story, however, cannot be traced further back than the 17th or 18th century. Also, it is at variance with the 10th century writers, who all agreed that the move took place in accordance with the saint's desire expressed in a vision. James Raine suggested that the legend was derived from the tremendous downpour of rain that occurred, according to the Durham chroniclers, on Saint Swithun's Day, 1315.
More probable is John Earle's suggestion that the legend comes from a pagan or possibly prehistoric day of augury. In France, Saint Medard (8 June), Urban of Langres, and Saint Gervase and Saint Protais (19 June) are credited with an influence on the weather almost identical with that attributed to St Swithun in England. In Flanders, there is St Godelieve (6 July) and in Germany the Seven Sleepers' Day (27 June). There is a scientific basis to the weather pattern behind the legend of St Swithun's day. Around the middle of July, the jet stream settles into a pattern which, in the majority of years, holds reasonably steady until the end of August. When the jet stream lies north of the British Isles then continental high pressure is able to move in; when it lies across or south of the British Isles, Arctic air and Atlantic weather systems predominate."