The National Weather Service confirmed at least 21 tornadoes impacted four states in the central US on December 15, during an unprecedented storm that brought weather warnings to some 100 million Americans and killed at least five.
The high-wind storm system, known as a derecho, brought hurricane-force winds, dust storms, wildfires, snow squalls, and heavy rain across the middle of the country, and spawned tornadoes in Minnesota, Nebraska, Wisconsin, and Iowa, where authorities had confirmed 13 twisters touched down.
This animation, released by NASA, shows the storm system developing from late on December 14 and sweeping across the United States on December 15 into the early hours of December 16.
“The derecho was spawned by the interaction of a deep-low pressure system over the Northern High Plains and a high-pressure system to the west,” NASA said. “This created a tight pressure gradient over the Rocky Mountains that generated fierce winds. The storm generated at least 55 hurricane-force gusts (those exceeding 75 miles per hour), breaking the previous one-day record (since tracking began in 2004). All previous records were set during the summer months.” Credit: NASA via Storyful