July 31 Events of the Past

July 31, 1987

A rare, class F4 tornado rips through Edmonton, Alberta,

killing 27 people and causing $330 million in damage.
 .

A tornado is a violent, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes come in many shapes and sizes, but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds less than 110 miles per hour (177 km/h), are approximately 250 feet (80 m) across, and travel a few miles (several kilometers) before dissipating. The most extreme can attain wind speeds of more than 300 mph (480 km/h), stretch more than two miles (3 km) across, and stay on the ground for dozens of miles (more than 100 km).

Various types of tornadoes include the landspout, multiple vortex tornado, and waterspout. Waterspouts have similar characteristics to tornadoes, characterized by a spiraling funnel-shaped wind current that forms over a body of water, connecting to a large cumulus or cumulonimbus cloud. Waterspouts are generally classified as non-supercellular tornadoes that develop over bodies of water. These spiraling columns of air frequently develop in tropical areas close to the equator, and are less common at high latitudes.Other tornado-like phenomena which exist in nature include the gustnado, dust devil, fire whirls, and steam devil.

Source: Wikipedia.org.