A tornado is part of a severe thunderstorm, and because thunderstorms occur all over the world, tornadoes are not restricted to any specific location. In reality, tornadoes have been recognized in every state, and on every continent, but Antarctica. Wherever the conditions are right, the possibility of a tornado is possible.
There are some parts of the world that are more prone to tornadoes than others. When cold, polar air comes against warm, subtropic air can create wind shears that may rotate into a storm cell. The United States averages approximately 1,000 tornadoes every year.
Tornado Alley has no defined boundaries but it includes central Texas, as far north as Iowa, and from central Kansas and Nebraska to western Ohio. Tornado Alley rarely has very violate storms and most tornadoes aren’t stronger than an EF3 (according to the Enhanced Fujita Tornado Damage Intensity Scale). There are only about 2% of tornadoes that rise above an EF3 each year. A tornado with an EF5 status can reach a wind speed of over 200 miles per hour.
Due to the fact that most thunderstorms gain their strength from solar heating most tornadoes occur during the afternoon and evening. Although, a tornado can occur at anytime day or night, they mostly happen when temperatures are lowest and radiation deficits are highest.
There is no defined season for tornadoes to occur, because they occur at any point during the year. In Tornado Alley most tornadoes occur during mid-summer, and rarely do tornadoes occur during the winter.
Not like rainfall or temperature, which may be measured by a fixed instrument, tornadoes are momentary and very unpredictable. If a tornado occurs in a place with few or no people, it is not likely to be documented. Regrettably, much of what we know as tornado alley was very thinly populated until the 20th century, so it is possible that many noteworthy tornadoes may never be known.
Since tornadoes are so unpredictable there are many times that residence only get a few minutes warning that a tornado is approaching. This makes it very hard to warn people to evacuate or find a safe place to stay until the tornado is over. Which may be a reason that there can be so many deaths associated with tornadoes. Meteorologists and storm chasers are always trying to find better ways to predict tornadoes better and more accurately so they will be able to give residents more warning.