You don't have to be a weatherman to know what the term weather eye means. Weather eye names "the eye that is quick to observe coming changes in the weather"; soon after that sense first appeared in print in the early 19th century, weather eye developed the metaphoric meaning "constant and shrewd watchfulness and alertness."

But today we cast our weather eye back even further in time, to the 13th-century coinage: weathercock. The physical weathercock names "a vane, often the figure of a cock, mounted so as to turn freely with the wind and show its direction." The figurative weathercock names "a person or thing notable for changing readily or often."

The story explaining how weathercocks came to grace so many church steeples hasn't changed over the centuries. According to legend, a 9th-century Pope decreed that every church steeple should be topped with a weathercock. The weathercock was an allusion to Saint Peter, the "rock" upon whom Jesus promised to build his temporal church. Remember that it was the apostle Peter who renounced Jesus three times before the cock crowed twice, and who then repented, weeping bitterly.