General Question

Berserker's avatar

Do leaves on a tree really indicate the coming of a storm?

Asked by Berserker (33514points) June 1st, 2011

I was often told that when all leaves on trees turned ’‘upside down’’, that this means a massive storm is up ahead.
Today we’re having really violent winds, I mean seriously…and most trees have their leaves like that. A storm is also announced…yet, the sky has been a bright blue and the Sun has been shining for hours. Where is this epic storm? What does it mean when leaves turn upside down like that?

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11 Answers

ANef_is_Enuf's avatar

It doesn’t have to be a storm. The leaves will turn when it is very humid or before it rains, period. It isn’t that it is necessarily going to storm.. it just means that the atmosphere has a lot of moisture – which makes the leaves “soft” and they sort of wilt. From the ground, it appears as if they are turning before it rains. :)

laureth's avatar

A storm is usually accompanied by a low pressure zone. Low pressure means that a lot of atmosphere (moving air, essentially) is rushing into the area, bringing the gunk along. It also pulls air upward, which is why the leaves do that – or so I heard.

Mariah's avatar

I’ve heard that too, but my assumption has always been that people say that because leaves do that when there are high winds, and high winds are also a sign of an approaching front, which storms often accompany. Correlation, not causation.

Berserker's avatar

All these answers make sense. It has been humid as hell today, still is. And I guess it is logical to think that it’s automatically the coming of a storm when the reasons for turning leaves can often be attributed to stormy elements.

ANef_is_Enuf's avatar

@Symbeline not all leaves will turn before the rain. Trees with thinner leaves are more prone to the phenomenon, and historically it was used in early weather prediction. It really isn’t reliable, because a muggy day will cause the same thing to happen.

Berserker's avatar

Yeah this is what I noticed today. Most trees I saw had turned leaves, especially big tall ones. But there were a few that didn’t. I just attributed it to the type of tree, rather than thick/thin leaves, but I guess in the end it’s the same thing lol.

Thanks for the info.

Kayak8's avatar

Where I live, it is the maple trees that will consistently show impending rain. It has nothing to do with wind, it is that the bottoms of the leaves are turned up and more visible in response to increased humidity.

Berserker's avatar

Plenty of maple trees here too, but no rain has shown up yet…still, humid as hell.

WestRiverrat's avatar

My granny told me that turned up leaves usually meant it would rain that night. It kind or makes sense, the hotter daytime air can hold more moisture than cooler night air can.

WasCy's avatar

Well, it’s a simple enough explanation, really, and it has nothing to do with humidity, at least not humidity as a cause.

In most of the US (most of the mid latitudes of the Northern Hemisphere, to be precise) the prevailing wind is from the southwest. That’s the fair-weather wind, and it’s the direction that most vegetation “grows into”. So trees and most plants have grown facing a southwest wind. The Coriolis Effect means that as the cooler air from the high pressure areas moves downward, it rotates clockwise (in the Northern Hemisphere, mid latitudes), and that’s what gives us the prevailing southwesterlies.

When the wind shifts to the east, that is very often a sign of bad weather, since the cyclonic wind is now coming from the opposite direction. The cyclonic winds (counter-clockwise) are caused by the low pressure areas that bring us bad weather, since the Coriolis Effect is opposite with the low pressure area vs. the high.

You can still have bad weather from the southwest, but winds from the east more often than not only bring bad weather. (And on the Eastern Seaboard, they also bring damp, humid air from over the Atlantic Ocean, hence the higher humidity.)

Garebo's avatar

I think it has to do with the rapid seasonal changes in barometric pressure combined with the spring trees growing new wood-how sexy is that, and they are filled with sap with a high molarity of solute; they are transporting upward through their xylem for photosynthesis-just a hunch.

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