US has world’s highest tornado risk — here’s why

The recent outbreak was December’s deadliest on record. 
 The four state tornado in the United States has reminded citizens of the destruction that looms over the eastern two-thirds of the country throughout the year. But why is this region so susceptible to these natural threats? Jim Duncan, a meteorologist, examines the key elements that put the lower 48 states in the centre of a not-so-sweet ordinate zone.