Tornado outbreaks in 2011 conditions similar to 1974?

What are the similarities in the ingredients that caused the 1974 tornado outbreak and the one we're seeing now? Please don't just say there is more instability, outbreaks from great plains cyclone model, helicity, low level jet activity, etc... I mean what is causing these factors to increase particularly? Is there something happening climatologically, or are there patterns from other years with more severe weather?