weather eye

sensitivity and alertness to signs of change in the weather.

a steady and astute watchfulness, especially alertness to change.

keep one's/a weather eye open, to be on one's guard; be watchful: He kept a weather eye open for new political developments.

Origin of weather eye

First recorded in 1830–40

"I'll keep my weather-eye open," replied the driver, getting on his box.

The Mysteries of Paris, Volume 2 of 6 |Eugne Sue
And I would have been better advised to keep my weather-eye open.

Beasts & Men |Jean de Bosschre
"Keep your weather-eye open, Bounce," said Martin, turning toward the dog.

The Cave by the Beech Fork |Henry S. Spalding
He screwed up his weather-eye (the one next his wife, of course, that being the quarter from which squalls might be expected).

The World of Ice |Robert Michael Ballantyne

To catch a person nodding; to find he has not his weather-eye open—Nunquam dormio!

The True History of Tom and Jerry |Charles Hindley

weather eye

the vision of a person trained to observe changes in the weather

informal an alert or observant gaze

keep one's weather eye open to stay on the alert