With Monday's strong storms this week and more likely, one question I received didn't ask about the wind damage, but why the leaves seem to flip upside down just prior to a storm's arrival.
When a storm approaches, we are all familiar with those gusty conditions that precede the onset of the rain. These gusty winds are a result of the downdraft created by the falling rain. The rain not only drags air down with it, but it also cools down the column of air it is falling within. This air can sometimes reach 100mph or greater, especially when the whole thunderstorm is collapsing. As the air slams into the ground, it has to go somewhere, so it spreads out.
Usually the strongest winds are in advance of the storm where the speed of the wind combines with the forward motion of the storm. We have already seen a number of damage reports from Monday. So the leaves you see flipping are a result of not just the unusually strong, gusty wind, but also the turbulence created near the ground. As these eddies form, the swirling air can actually blow upward in spots creating a real weird looking tree when the leaves all flip up.
The picture accompanying this blog is a wind product we sometimes show on our WBTV weathercasts. It is a wind forecast, in this case for midday Tuesday of this week. You can see the computer model depicting two areas of strong to damaging winds (red and purple), likely associated with clusters of thunderstorms developing again. One is over the Piedmont of North and South Carolina, and a second region is coming through the mountains. You can't take model data too literally on timing or location, but it still offers a guide as to what the atmosphere could produce on a given day.