Tornadoes - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 306

Figure 6.2b. Tornadoes with condensation funnels: May 12, 2004, near Attica, KS, silhouetted
(top left); June 10, 2004, southwestern Nebraska, fully illuminated (top right); May 22, 1981,
near Binger, OK (middle left); May 22, 1981, near Binger, OK, dust obscuring center of
tornado (middle right); May 13, 1989, near Hodges, TX, dissipating stage, when gust front
from parent storm makes condensation funnel lean with height (bottom left); May 13, 1989,
near Hodges, TX, dissipating stage when condensation assumes a narrow, ropelike appearance
(bottom right) (photographs by the author).
Wind speeds in tornadoes range from 20 to 140m s 1 , although it is not
generally agreed what the lower cutoff wind speeds are, and some rather weak
vortices (producing only rotating dust whirls) have been reported as tornadoes.
The translation speed of a tornado is important in determining the lower speed
limit: A rapidly moving (e.g., at 20m s 1 ) very weak vortex (e.g., with azimuthal
wind speeds of only 20m s 1 ) can inflict significant damage on the side where the
ground-relative wind is highest. Efforts have been made to estimate wind speeds in
tornadoes based on the nature and extent of the damage they inflict ( Figure 6.5 ) .
The Fujita ''F-scale'', devised by Ted Fujita in the 1970s, ranges from F0