Severe Weather Awareness - Tornado Basics

Wisconsin Tornado and Severe Weather Awareness 

Part 1 - Tornado Basics

Tornadoes are one of the most powerful and violent storms that nature can produce.  They come in all shapes and sizes and can occur in every state, on any day and at any hour.  All tornadoes can be a direct threat to your safety.  Each year they constitute a major hazard across the U.S. 

A tornado is a violently rotating column of air (wind) that extends from the base of a cumulonimbus cloud down to the ground.  One cannot see a column of air and wind that is rotating on a vertical axis between the cloud base and the ground unless there is a visible condensation funnel inside the invisible tornado, or one sees rotating dirt/debris at the ground level.

There have been many documented cases in which a tornado was damaging structures and vegetation but there was very little or no visible condensation funnel.  Most people refer to the condensation funnel as a funnel cloud.  Since you can have a tornado with little or no visible condensation funnel, the condensation funnel is not the tornado.  

For many years it was assumed that tornadoes grew downwards from the base of a cumulonimbus cloud to the ground because the condensation funnel visibly grew downwards.  Consequently, this gave people the false perception that tornadoes touched down.  It is true that the condensation funnel does grow downwards, but a nearly invisible tornado can develop between the cloud base and ground prior to the development of a condensation funnel.  In most cases, eventually a condensation funnel does develop from the cloud base down to the ground, but this may happen after a tornado has already caused damage.

Wisconsin Tornado Statistics

• Peak tornado season is May through July.
• Peak hours are between 3 pm and 9 pm but can occur at any time.
• Peak hour is between 6 pm and 7 pm.
• Average of 23 tornadoes annually.
• Average of 1 fatality each year due to tornado-related injuries. 
• Average tornado lasts about 7.1 minutes and has a path length of about 3.7 miles and path width of about 118 yards.

Tornado Watch vs. Tornado Warning

Be sure you understand the difference!  Many people confuse watches and warnings. 

• A tornado watch is issued to give you advance notice that the development of tornadoes is possible in your area.  This gives you the time to make plans for moving to a safe shelter quickly if a tornado is sighted.
• A tornado warning is an urgent announcement that a tornado has been reported by a person or is imminent due to Doppler Radar information.  Take immediate action.  Move quickly if you are in the tornadoes path.  Seconds can save your life.

Visit the Storm Prediction Center Online Tornado FAQ for much more information on Tornadoes