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Maple Leaves Answer
Mon Sep 01, 2003
Listen in RealAudio 
Hi, I'm Bryan Yeaton, and this is The Weather Notebook. Last month, we asked a Brainstorm
about why leaves show their light-colored bellies before a thunderstorm. Here was one
answer:
The leaves on the trees flip over before a thunderstorm so they can give birth to baby
leaves.
Well, with my knowledge of tree propagationwhich is not terribly in-depthI'd still say this is
not the correct answer. I wonder why he didn't leave his name.
Some of the answers did at least have a meteorologic flair, such as this one from George
Dussey Braun, who listens on Mississippi Public Radio:
It would seem to me that it is probably or possibly caused by changes in barometric
pressure.
Actually, it's not the pressureat least not directly. Martha Gwynn, of Marietta, Ohio
guessed:
Could it possibly be the updraft?
In fact, it is!
Here's what Tim Owens, a WFYI, Indianapolis listener said:
The low pressure causes the air to rush upward which flips the leaves over]
Bill Eccles in Terre Haute, Indiana, who listens on WFIU, adds some detail.
Thunderstorm development requires a considerable amount of upflow activity, be it surface
heating or whatever. And this upflow lifts the leaves and makes their underside show more
clearly. And the result is we get the warning that there is the possibility of storms, or
there is at least, a good amount of upflow.
There is also some thought that the downdraft of a thunderstorm can also produce the leaf
inversion. But it's not about babies. Definitely not.
Thanks to everyone who called or wrote. The Weather Notebook is funded by grants from Subaru
of America, and The National Science
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