Downward rushing currents of air, or downdrafts, occur along the leading edge of almost all thunderstorms and along the trailing edge as well in some cases. This process, which can bring a welcomed breeze on a hot summer day, can produce winds that are as damaging as a tornado. Strong localized downdrafts are called downbursts. These intense concentrations of sinking air fan out upon striking the earths surface in what meteorologists and weather spotters call straight- line winds. They may be accompanied by a roaring sound similar to that associated with tornadoes. Thunderstorms which produce downbursts typically produce several in succession of various sizes and intensities, which will often mislead victims into thinking that it was a tornado.
Damage caused by these straight-line winds can often appear similar to damage produced by a tornado, especially when there appears to be a well defined damage path or a concentrated area of damage next to a relatively undamaged area.
In Georgia, downdraft winds from thunderstorms will often reach destructive force more often than a thunderstorm will produce a tornado! These winds can have speeds of up to 60 mph...and can even exceed 100 mph! What makes these winds so damaging is the rapid increase in local wind speeds when downbursts strike. Winds that rapidly jump from 10 mph to 60 mph can produce more damage than a sustained 60 mph wind. Frequently, damage that is attributed to tornadoes is actually due to straight-line winds of a downburst. In Georgia, the frequent occurrence of downburst winds makes it imperative that a Severe Thunderstorm Watch/Warning be taken as seriously as a Tornado Watch/Warning.
The National Weather Service defines a severe thunderstorm as one which produces: