A tornado is part of a convective storm which is not limited to any specific geographic location (barring Antarctica). Generally, the most favorable environment for tornadoes is between 30 and 50 degrees in northern and southern latitudes. Heavy storm activity, which causes tornadoes occur when cold, polar air clashes with warm, humid, subtropical air (generally from the Gulf of Mexico for the mid to southeastern states). This creates convective precipitation along the boundary and with the added wind speed, which often times can go at different speeds at different levels of the atmosphere and this causes the rotation within a storm cell. Just this month we have seen Oklahoma City get hit by a monster tornado with a rating of EF 4 which is just shy of the one that hit the very same area in 1999. The one that hit May 3rd, 1999 was an EF 5-or the finger of God. An the rating of a tornado is based on the Fujita Tornado Scale and is known by how much the tornado “eats.". The tornado that hit Oklahoma City this May has seen more dead then the 36 people from the disaster of 1999, and we may see an increase as clean-up continues.
It is known that places that receive the most tornadoes happen to be in the bread baskets of the world. This is no surprise in that these fertile agricultural areas receive their precipitation from the convective storms that occur in those latitudes. The U.S. leads the count in tornadoes with an average of 1,000 a year. Canada is a distant second at 100 per year with other locations experiencing frequent tornadic occurrences in “northern Europe, western Asia, Bangladesh, Japan, Australia, New Zealand, China, South Africa and Argentina. It is important to note that the United Kingdom has more occurrences of tornadic activity but all of these are relatively weak.
In the U.S. the areas that receive the disproportionate amount of activity is Florida and an area called “Tornado Alley” which is in the south-central U.S. in the plains area (i.e. Oklahoma). These areas receive the most violent of tornadoes, typically an EF2 or greater. However, 77% of tornadoes are in the weaker EF0-EF1 and 95% are below the EF3 range. So the probability of getting something like an EF5 is only 0.1% (1, par 4). Consequently, with the average being 1000 tornadoes each year in the U.S., 20 of them are going to be incredibly violent with the possibility of being an EF5.
Ten of the deadliest tornadoes, according to the NOAA, happened in the mid-west of the United States. The “Tri-State Tornado” in March of 1925 which killed 695 people, a couple thousand injured, and ran from Missouri to Illinois to Indiana cutting a 300 mile swatch through the three states. This was an F5 with winds in excess of 260 mph. Another was the “Natchez Tornado” during May 1840 which killed 317 people, injuring 109 (which may not be accurate because they may not have included slaves) and this ranged from Louisiana to Mississippi. The “St. Louis Tornado”, which happened late May in 1896 in Missouri and Illinois, killed 225 and injured another 1,000 and similarly the “Tupelo Tornado” killed 216 people with 700 injured during April 1936 in northeastern Mississippi City. The “Gainesville Tornado” killed 203 people during early April of 1936, in Gainesville, Georgia which also injured over a thousand people. In Texas, Oklahoma, and Kansas the “Woodward Tornado” during the April month of 1947, killed 181 people, injuring 970, and cutting a mile wide swatch in some areas. The recent tornado that occurred in Joplin, Missouri during May of 2011 killed 158 people, injured over a thousand and was on ground for over 22 miles. The “Amite/Pine/Purvis Tornado” which occurred late April 1908, left seven houses in Purvis, Mississippi killing 143 people and injuring over 700. In New Richmond, Wisconsin 117 people were killed and 200 injured during the summer of 1899 by the “New Richmond Tornado." And last but not least the “Flint Tornado” which killed 115 and injured 844 more on June 8th of 1953 in Flint Michigan. This was to be the “deadliest twister ever recorded in the state." While the recent Oklahoma disaster was caused by an apparent EF5, it was not as deadly as the top ten. Never the less, the Oklahoma twister was extremely damaging and dangerous.