DENVER — Violent tornadoes can happen just about everywhere on earth, but there are far more in the United States than anywhere else, thanks to a combination of factors.
The Gulf of Mexico frequently supplies the first ingredient, packing the low-level air with ample moisture, which warms over the continent. Then cooler and drier air descends off the Rocky Mountains and moves over top of the Gulf moisture, creating instability.
Powerful thunderstorms form when warm moist air rises quickly into the atmosphere. The stronger the thunderstorm, the more likely it is to produce a strong tornado.
That meets up with the cooler and drier air as it descends from the Rocky Mountains. The result is the most EF-4 and EF-5 tornadoes in the world. Some spots average more than five a year.
The relatively flat American prairie land also helps sustain the rotating thunderstorms known as supercells, which in the right conditions can create tornadoes that are more than a mile wide and stay on the ground for more than an hour.
There are other places that have the environment necessary to create violent tornadoes, but they don’t last as long as they do in the United States, and they are much less frequent.
For example, the Ganges River basin south of the Himalayan mountains during the Indian monsoon. The deadliest tornado of all-time hit Bangladesh in April 1989, killing nearly a thousand people.
Three of the top 5 deadliest tornadoes of all-time happened in Bangladesh, but still, violent tornadoes there are not anywhere near as frequent as they are in the U.S.
Colorado has never had a violent EF-4 or EF-5 tornado, but this was the first year there were multiple EF-3 tornadoes since 1990. One hit Yuma and another hit Holly.
The last time someone in Colorado was killed by a tornado was Windsor 2008.
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