MADISON (WKOW) -- Tornadoes are one of mother nature's most incredible and destructive phenomena. Their damage is obvious, but the tornado itself can be invisible to the naked eye.
Rusty Kapela of the National Weather Service says a tornado is nothing more than air and wind that is violently rotating. "It's a column of air violently rotating and that's all it is, we can't see air, no one in this room can see air or wind until you get a lot of debris."
Rising air within the thunderstorm updraft tilts rotation from horizontal to vertical, creating an area of rotation, two-six miles wide, where most tornadoes form.
Wisconsin averages 21 tornadoes a year and 2008 was an active season.
"It was unusual in that it was the third busiest: we had 38 tornadoes and previously two big years. 2005 with 62 as we all still remember and also 1980 where we had 43, so it was the third busiest."
Tornadoes come in many shapes and sizes. 88 percent of all tornadoes are categorized as weak, causing less than 5 percent of tornado deaths. The winds of weak tornadoes rotate at less than 100 mph, and generally last less than 10 minutes.
A weak tornado struck Madison on June 23, 2004. The 200-yard wide tornado tore an 8-mile path from Middleton into Madison. This tornado damaged trees, but luckily no one was hurt.
11 percent of all tornadoes are strong. These tornadoes cause nearly 30 percent of all tornado deaths. They can last 20 minutes or longer and generate winds of 110 to 205 mph. The half-mile wide tornado that struck the north side of Stoughton on August 18, 2005 was a strong tornado and caused damage for 20 miles, killing one and injuring 21.
Less than 1 percent of all tornadoes are categorized as violent, but account for 70 percent of all tornado deaths. They can last more than an hour and generate winds greater than 205 mph. The massive tornadoes that struck Barneveld on June 8th, 1984 and Oakfield on July 18, 1996 were violent tornadoes. These two monsters were the costliest in Wisconsin history. The Barneveld tornado was Wisconsin's 10th most deadly, killing 9 and injuring 200.