Have you heard the old wives' tale that the leaves on a tree flipping over is a sign that rain is in the forecast? 

This is one old wives' tale that is based in some truth, but it may not be why you think. Leaves of a tree do sometimes flip over before it rains, but it's not because of anything the leaves themselves are doing in anticipation of the precipitation. Instead, it's a response to the weather conditions that precede some rain events. 

Because of this, the leaf flipping is usually a sign that rain is imminent, not part of the long-range forecast,  according to WGN-TV's Tom Skilling. This is because the leaves are changing position because of weather conditions that typically develop just before rain moves in.

One of the primary factors that can cause leaves to flip over before it rains is wind. As summer storms and rain events move in, gusty winds often precede them, causing leaves to flip over and show their silvery side, according to the Ohio State University Extension.

This happens because as trees grow, their leaves typically grow in accordance with the prevailing wind for the area. Winds from incoming storms typically go against the prevailing wind, and the force of the wind causes the leaves to flip. Of course, sometimes non-prevailing winds sweep through an area without any associated rain or storms, and this, too, can cause the leaves to flip.

Another factor that can cause leaves to turn over just before it rains is humidity. As you've no doubt noticed, rain and storms are often preceded by or accompanied by humid air. The humidity can soften the leaves, causing them to hang more limply on their branches, Farmers' Almanac reports. The softening of the leaves can also make them hang in a flipped position or flip more easily in the breeze.

Weather-centric old wives' tales like this one predate scientific weather forecasting, going back to a time when people used their observational skills to notice patterns associated with particular weather events, Farmers' Almanac reports. One generation passed this knowledge onto the next and so on, which is why they still persist today at a time when it's easy to find out if rain is in the forecast.

This also explains why many of these sorts of old wives' tales are based on some scientific truths, according to Skilling. People from hundreds of years ago noticed that flipped leaves often preceded rain or a storm because the weather conditions ahead of these sorts of weather events do sometimes cause the leaves to flip. 

And flipped leaves aren't the only signal plants may provide of the upcoming weather. Like leaves, pine cones also react to humidity, so if you see them all closed up it's a sign of high humidity levels and possible rain. Flowers, too, are said to be more fragrant before it rains because the increased humidity makes their scent stronger, according to the Ohio State extension.