“When leaves show their undersides, be very sure rain betides.”
Weather folklore has always been a big part of the Farmers’ Almanac. Long before there were scientific instruments to measure and predict the weather, people used the only instrument they had: the power of observation.
“Old wives’ tales,” like the one recorded above came about because people noticed patterns in nature, and passed those observations down from generation to generation. Whereas today, we can just switch on the local news (or crack open a Farmers’ Almanac) to get a weather report, our ancestors had to rely on their senses.
But does seeing the undersides of leaves really mean rain is on the way? In this case, our forebears were definitely onto something. The leaves of deciduous trees, like maples and poplars, do often to turn upward before heavy rain. The leaves are actually reacting to the sudden increase in humidity that usually precedes a storm. Leaves with soft stems can become limp in response to abrupt changes in humidity, allowing the wind to flip them over.