July 15 is St. Swithin's Day. Swithin, also spelled Swithun, was Bishop of Winchester from 852 to 862. In England many people still believe that, if it rains on St. Swithin's Day, it will rain for 40 days consecutively. On the other hand, if it is clear on St. Swithin's Day, nice weather will prevail for 40 days thereafter.
Organizers of the forthcoming London Olympics are out, even now, doing their anti-rain dance.