Over the past few weeks, hundreds of tornadoes have slammed the U.S Midwest and Great Plains region.
In fact, the U.S. recently broke the previous record of the number of consecutive days that twisters touched the ground. Starting on May 17th, there were 13 such days, breaking the record set in 1980. On May 27th alone, there were 46 confirmed tornadoes!
What causes tornadoes, and why has this year been so unusual? Let’s take a look!
How do Tornadoes Form?
A tornado is a vertical column of quickly rotating air, that extends from the clouds down to the ground. Its winds can reach 250 miles per hour and its path on the ground can be up to a mile wide!
A tornado can form when warm humid air collides with cold dry air. When the warm air is lifted up through the cold air, it causes an updraft, which then starts rotating when the accompanying storm winds vary in speed and direction.
As the updraft draws in more warm air, its rotating speed increases, and a funnel cloud forms. The funnel continues to grow and will eventually descend from the cloud. When it touches the ground, it officially becomes a tornado.
While tornadoes occur in many countries around the world, the U.S. has the vast majority of them. The country gets an average of 1,200 tornadoes every year, and Canada is second with about 100 tornadoes.
The region of the U.S. that has had the most frequent and powerful tornadoes is commonly referred to as Tornado Alley. It is not a fixed region but generally covers the area bordered by central Texas on the south, Iowa on the north, central Kansas on the west and Ohio on the east.
What Happened This Year?
There have been 225 confirmed tornadoes in the U.S. since May 17th. While May is typically the peak month of the tornado season, the numbers this year have been unusually high.
Victor Gensini, a professor of meteorology at Northern Illinois University, has been studying the effects of changes in our atmosphere and tornadoes. He believes that this year’s Madden-Julian Oscillation (MJO), a periodic swing in temperature and moisture that originates in the Indian Ocean and then moves eastward towards the Pacific Ocean, is responsible for the burst of tornadoes.
In late April, Gensini saw a significant increase in activity in the atmosphere over the Indian Ocean. He predicted these atmospheric waves would reach the United States in late May, creating severe weather patterns that are conducive to thunderstorms and tornadoes.
For now, the storms caused by this MJO appears to be weakening. However, scientists warn that the U.S. is still in tornado season, which is typically from late spring to early summer. Tornadoes can occur from other disturbances in the atmosphere, not just MJOs.
Sources: Washington Post, VOX, National Geographic, NOAA, weatherstationadvisor