The assault on the Mid-West by a total of 81 tornadoes has left 8 people dead, and more may be still buried amongst wreckage.

Indiana saw 23 tornadoes and Kentucky 13, but Illinois suffered the brunt of the storm when it was struck by an incredible 43 tornadoes, leaving at least six people dead and seven counties declared disaster zones. The massive weather system rampaged through a total of 11 states including Michigan, where another two people were killed, and Wisconsin, Iowa, Missouri, Ohio, Tennessee, West Virginia, Pennsylvania and western New York were also affected.

The massive late storm was highly unusual, and followed one of the quietest tornado seasons in 40 years. The north has never been given ‘high-risk" weather predictions from the National Oceanic and Atmospheric so late in the year, and people are asking how such a catastrophic weather system occurred in November.

A study, which was published earlier this year in the journal of the Proceedings of the National Academy of Sciences, actually predicted the advent of more severe storms as the evidence found suggested that global warming would begin to create favourable conditions for major weather events on a more regular basis in the US.

The findings were based on the latest computer models using the two main atmospheric ingredients thought to cause storm formation, one of which is ‘convective available potential energy’, or CAPE, created as air in the lower atmosphere warms. In order to create a severe storm, CAPE must meet with strong vertical wind shear.
Previous studies had concluded that global warming would increase CAPE but decrease shear, so the two effects would cancel each other out, but this latest simulation, derived by climate scientists Noah S. Diffenbaugh and Martin Scherer of Stanford University and Robert J. Trapp of Purdue University, uncovered a pattern not noted in the previous models.

"What we’ve found is that the reduction in shear actually falls on days when there’s low CAPE," explained Diffenbaugh.

So when CAPE is elevated, wind shear is also likely to be high and this indicates that global warming could increase the frequency of environments conducive to the formation of severe storms.
Diffenbaugh said that the model was unable to predict with any certainty whether future storms would be more powerful or how and when they would form, but this latest event in the Mid-West appears to add weight to their theory.