July 5, 2004

Dear Tom, What controls tornado size? Some are rope-like while others look like walls of wind. Liz Thomas, Hometown, Ill. Dear Liz, At ground level, inflow winds spiral into a tornado, then corkscrew upward within the tornado vortex itself. National Weather Service tornado researcher Brian Smith says inflow strength and amount determine a tornados actual width, but other factors influence its apparent width: your distance from the tornado, cloud base height, moisture content of the air (condensation makes the tornado vortex visible), and availability of dust and debris (which also make the vortex visible). When you are very close to a tornado, it fills much of the approach horizon and resembles a wall. In its dissipating minutes, a tornado tightens and shrinks into a slender rope, then disappears.

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July 5, 2004

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