Tornadoes are violently whirling wind, characteristically accompanied by a funnel-shaped cloud extending from a cumulonimbus cloud. A tornado can be from a few yards to about a mile wide where it touches the ground, with an average width of a few hundred yards. It can move slowly or speed along at more than 60 mph and may travel for distances ranging from short hops to several miles, causing extensive damage. The funnel is made visible by the dust that it sucks up and by condensation of water droplets in its center. Most tornadoes spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Movement is usually from southwest to northeast.
However, they have moved in other directions and tornadoes associated with hurricanes may move in a westerly direction. A tornado is formed when cold air overriding a warmer air mass breaks through the upper boundary formed by the two air masses and in a violent rotating column descends because of its heavier weight. This creates a hole in the air mass boundary allowing the warm, lighter air to rush upward into the cold air. While tornadoes in Texas can occur in any month and at all hours of the day or night, they occur with greatest frequency during the late spring and early summer months and during late afternoon and early evening hours. This is particularly true in Polk County.