Tornadoes are one of nature’s most violent and destructive forces. Every year, hundreds of tornadoes touch down across the United States, mostly in a region nicknamed “Tornado Alley” which includes parts of Texas, Oklahoma, Kansas, Nebraska, and South Dakota. But in recent decades there has been evidence to suggest that Tornado Alley may be shifting further east, bringing more frequent and devastating tornadoes to states like Arkansas, Missouri, Illinois, Indiana, Kentucky and Tennessee.
What is Tornado Alley?
Tornado Alley refers to a region in the central United States that sees the highest concentration of tornadoes each year. The boundaries of Tornado Alley are not officially defined, but it is generally understood to include parts of:
- Texas
- Oklahoma
- Kansas
- Nebraska
- South Dakota
On average, this region sees over 1,000 tornadoes per year. The most tornadoes on record occurred in 2004, when 1,817 tornadoes tore through the region.
Several factors make Tornado Alley so prone to tornado formation:
- Proximity to the Rocky Mountains causes dry, high-altitude air from the west and south to meet warm, humid air from the Gulf of Mexico. This collision creates instability in the atmosphere.
- A northward jet stream brings cold arctic air from Canada, adding to the atmospheric instability.
- Flat terrain allows thunderstorms to gain strength and organize into supercells – rotating updrafts that spawn tornadoes.
Evidence of an eastward shift
While Tornado Alley has always been centered over the Plains states, meteorologists have noticed some changes in recent decades. More tornadoes appear to be developing further east into states like Arkansas, Missouri, Illinois, Indiana, Kentucky, and Tennessee.
Some key evidence of this shift includes:
- Arkansas had more tornadoes than Kansas for 15 years straight from 1999-2013.
- From 2000 to 2013, Mississippi had more tornadoes than Nebraska.
- Tennessee had more tornadoes than Kansas in 5 out of 15 years between 1999 and 2013.
- Indiana and Kentucky now have more tornadoes in an average year than South Dakota.
Meteorologists documented 343 tornadoes in Arkansas, Missouri, Illinois and Indiana in 2017 – the highest number ever recorded east of Tornado Alley.
Major tornado outbreaks have also impacted these states in recent years. In 2013, 7 tornadoes struck Illinois and Indiana in a single November outbreak, including an EF-4 that killed 6 people in Illinois. In 2012, an outbreak generated 32 tornadoes across the Ohio River Valley region.
Why is this happening?
Scientists are still researching the exact causes of this apparent eastward shift. Some factors that may be contributing include:
- La Niña – This climate pattern features cooler than normal temperatures in the Pacific Ocean near the equator. Some research shows La Niña increases tornado activity further east.
- Stronger storms – Storms are becoming more intense further east for reasons not fully understood. Stronger storms may be better able to spawn tornadoes farther east than weaker storms.
- Earlier spring warmth – Warmer spring temperatures east of the Rockies may help make the atmosphere more unstable earlier, allowing for more March and April tornadoes.
More research is needed to better understand if climate change or natural climate cycles are also playing a role in this shift.
Impacts of an eastward shift
An eastward expanding tornado threat has serious impacts and raises concerns:
- Higher tornado risk for states less prepared – States further east have less experience preparing for, responding to, and recovering from significant tornado disasters.
- More densely populated areas affected – The risk is higher for tornadoes striking heavily populated cities east of Tornado Alley.
- More vulnerable structures – States further east have more masonry construction and fewer basements, leaving structures more exposed.
- Higher likelihood of nighttime tornadoes – Longer warm seasons may allow some tornadoes to form after dark, when they are twice as likely to kill.
Meteorologists and emergency planners caution that residents further east may need to increase their awareness and preparedness as the traditional boundaries of Tornado Alley appear to shift.
Conclusion
Evidence suggests tornado activity is increasing in states east of Tornado Alley, placing more people and property at risk. Scientists are working to better understand the causes, while communities further east may need to adapt to this expanding tornado threat. But with proper preparedness and warnings from meteorologists, tornado disasters can be prevented despite any shifts in Tornado Alley’s boundaries.