10 March 2011
An EF-2 tornado hit Theodore, Alabama on Wednesday and caused significant damage. The tornado was rated an EF-2 by meteorologists at the local NWS office in Mobile, and that indicates wind speeds of 180-218 km/hr (110-135 mph).
The image below shows the track of the tornado. Notice the hardware store in the image (between the two EF-2 triangles). There were several security cameras running at the time the tornado hit and the video is pretty scary.
The video from the cameras is below:
Here is the outside camera:
There is another related video I came across today and this is from Austria. It’s not a tornado but what is usually called a dust devil or a land spout. They are actually water spouts on land, and not technically tornadoes. No dust in the video but well worth watching.
The long plastic sheets over the fields are very likely what caused the cyclone to develop. They form due to differential heating of the ground. In this case, the air over the white sheets was certainly cooler than the air over the dark green and brown ground. A horizontal rotation develops as cool air rides beneath the rising warm air and all it takes is for a breeze to turn the rotation vertical and off it goes!
Once the rotation starts, the conservation of angular momentum will cause it to spin up and strengthen, drawing in more air. Those sheets weigh 60 kg each! Knowing the length of each sheet allows an estimate of the wind speed, and in this case about 100km/hr. This wind speed is pretty typical of a well developed land spout!