This year has witnessed nearly 900 tornadoes ravaging over 30 states, causing fatalities, demolishing structures, and resulting in billions in damages. This spate of tornadoes began in mid-March, with atmospheric conditions repeatedly aligning to create these powerful storms, and the tornado season is still not concluded.

Understanding Tornado Formation

Jana Houser, a tornado expert at Ohio State University, explains that tornadoes originate from thunderstorms, specifically those known as “supercells,” which contain a rotating updraft called a mesocyclone.

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To form a supercell, certain atmospheric conditions are necessary: warm, moist air near the ground and cooler, drier air above. This setup creates instability due to the rising of the warmer, lighter air. Additionally, wind shear is crucial, involving changes in wind speed and direction with height, creating a horizontal rotation. An updraft then lifts this rotating air, intensifying its spin, transitioning from a slow bicycle wheel spin to a rapid top spin.

However, not all supercells generate tornadoes, Houser notes. For a tornado to form, ground-level rotation must connect with a powerful updraft aloft, akin to a figure skater pulling in their arms to spin faster.

Global and National Tornado Hotspots

Tornadoes can occur anywhere with the right conditions—from Argentina to Bangladesh. However, the U.S. experiences the highest average number of tornadoes due to its unique geography. Warm, moist air from the Gulf of Mexico and cool, dry air from over the Rockies collide, particularly over the central U.S., creating an ideal setting for severe storms, an area often referred to as Tornado Alley.

In recent years, shifts in climate patterns have seen the emergence of a “new Tornado Alley” about 400 to 500 miles east of the traditional one, influenced by the eastward expansion of moist air from the Gulf.

The Seasonal Nature of Tornadoes

Spring is typically the peak season for tornadoes, as Houser explains. The season acts as a bridge between the cold of winter and the warmth of summer, creating perfect storm conditions. Unlike spring, autumn sees a delay in tornado activity which picks up later in the season as the atmosphere cools.

As the season progresses, the peak times for tornadoes shift northward: starting in the Gulf Coast early in the spring, moving to the Southern Plains in late spring, and reaching the Northern Plains and upper Midwest by mid-summer.

Factors Behind the Intense Tornado Activity This Season

As of mid-May, the U.S. has recorded about 886 tornadoes. “This is on the higher end for this time of year,” says Rich Thompson, chief of forecast operations at the National Weather Service’s Storm Prediction Center. Particularly active periods in mid-March and early April significantly contributed to the higher numbers.

The jet stream, a fast-moving band of air in the upper atmosphere, plays a pivotal role in shaping the season’s activity by influencing storm tracks and the interaction of warm and cool air masses. “We’ve seen periodic high-energy systems this spring,” Houser adds, which have effectively triggered these severe weather events when conditions align.