Chasing Tornadoes

JW: "Unfortunately, very few tornadoes have had quantitative measurements of their windspeeds. The highest windspeeds ever measured were about 135 m/s in the tornado that went through Oklahoma City on 3 May 1999.

NOAA Fury on the plains - the tornado that struck Oklahoma City in 1999

But it is very unlikely that this was the strongest tornado ever. It just happened to be measured by us. These were measured with the Doppler on Wheels radars. The traditional fashion in which tornadoes are categorized is the Fujita scale. But, this only measures the intensity of damage that the tornadoes have actually caused. A very powerful tornado passing over open country (and 99% of the country that tornadoes cover is open country, particularly in the sparsely populated tornado alley) will only cause F0 damage but a weaker tornado passing through a town might cause F4 damage. The Fujita scale does not measure windspeeds. It is often misused by the media and public. We propose that a Potential Fujita scale, similar to the Saffir-Simpson scale used for hurricanes be adopted. The PF scale will represent our best estimate of the actual windspeeds in a tornado, and its potential for doing damage."

FS: How do tornadoes form?

NOAA Tornado alley in springtime - the Midwest USA is the most tornado prone place in the world

JW: "The glib answer to that is we do not know. That is why we are studying them. We know the basic processes by which rotation is generated in supercellular thunderstorms. But we do not understand how and why and when these rotations, called mesocyclones, produce more intense, smaller-scale rotations called tornadoes. We do not know how to predict when a particular supercell will produce a tornado. We cannot forecast the size, strength, or lifetime of a tornado. In short, even though major strides have been made in the understanding of tornadoes and tornadogenesis in recent years, we have a long way to go."

FS: Why do tornadoes appear more regularly at certain times of the year and why in only certain parts of the world?