Diagnosing a daily index of tornado variability with global reanalysis

The recent record setting tornado outbreaks in April 2011 has spurred a lot of discussion and debate of the causes of this record setting month. Global warming and the decaying La Niña were both common causes suggested as the reason behind such a destructive tornado season. Due to the inhomogeneity of the observed tornado record, there are few published studies that relate climate variability to occurrences of tornados. We employ a method developed by Harold Brooks and co-authors in 2003 that discriminates tornadic and severe weather soundings from everyday convection to circumvent the problems with the observed tornado record. We will show how this index, derived from the CFS-R, realistically reproduces the observed variability in tornadoes, and the relative impacts of different modes of climate variability on tornadoes over the United States. This analysis will provide a baseline that will be expanded to climate model simulations of the 20th Century and future projections.