What is the I-44 Tornado Corridor?
There are several regions of the world where tornadoes have a tendency to touch down on a regular basis, but the 177-kilometre (110-mile) strip of land that runs from Oklahoma City to Tulsa is one of the most notorious.
It follows part of the St Louis to Wichita Falls Interstate 44 (hence the name) and has seen hundreds of destructive tornadoes tear down its length in the last century. The worst of these have ploughed a strip straight through Oklahoma City itself and, on 3 May 1999, no less than 70 touched down in the region. One of these was a devastating F5 on the Fujita scale that killed 40 people, left thousands homeless and caused $1 billion (£620 million) of damage.
Conditions at spring time make the I-44 corridor ripe for tornadoes: as warm, moist air drifts north from the Gulf of Mexico across the southern states, it’s met by cool, dry air moving high off the tops of the Rocky Mountains to the west. Combined with the huge, flat expanses of land in the region, it’s perfect for twisters.