Wednesday, June 17, 2009

A coming storm

Does today’s photo suggest anything to you? Let me give you a hint. It’s about the weather.

The leaves in this morning’s photo are turned inside out or upside down or however you wish to describe it. In any event, you are mostly looking at the underside of the leaves. Where I’m from, this is a sign of rain. Maybe it’s a sign of rain where you are from too or perhaps this is one of those signs that is only well-known in my region. I can’t answer that one.

I’ve heard various explanations for why this happens. I’ve heard that updrafts ahead of a rain cause it. I’ve heard the underside of leaves are more porous to gulp moisture out of the air. I have a slightly different theory of my own that I’ll get to in a bit.

First, the porous explanation: I have no idea. It sounds a little off to me. Unless the weight of the leaves is different from the top side to the bottom, I can’t figure out how this would work.

Second, the updraft theory. This says that right before a rain you get a change in wind direction or updrafts that moves the leaves this way. This one sounds sort of okay to me, except that I often see this phenomenon hours before the rain hits and not just moments or minutes before rain.

Here’s my own theory. It’s the addition of extra moisture in the air. On dry days when you have a breeze, the leaves and twigs just bend and flow with the breeze. But when the air is moist, the air is also heavier with that moisture and this affects how the leaves blow. This explains why you will sometimes see upside-down leaves even a day or so ahead of the rain, if the moisture is in the air ahead of the upcoming storm.

News from Roundtop: I will be offline for a few days to hike with kids from Adventure Camp and introduce them to a little nature study. See you next week (and maybe before but don’t count on it).

1 comment:

The-Grizzled-But-Still-Incorrigible-Scribe-Himself! said...

Have a great hike!

Re. leaves…I kinda favor a change in prevailing winds. I say that because I don't always see leaves exposing their undersides before each and every storm; but on the times they do and I can remember to check, the wind is usually blowing from a direction other than the typical westerlies—i.e., west, southwest, northwest.

Just my guess/reasoning, though. (I do not believe in the porous "let's flip upside-down and get a drink" theory, however.)