How does a tornado start?

How does tornado alley start?

• Answer:

  It is difficult to define the start of Tornado Alley as it is a region, not an event. The steps toward its formation took millions of years as North America took on its modern geography with the formation of the Rockies and the Great Plains. The final piece likely came into play at the end of the last ice age when the climate across North America became warm enough to support significant tornado activity.