something not only of this magnitude, but at this time of year? >> it is remarkably rare to see a strong tornado strike as far north as illinois and kentucky in this time of early winter, very rare. yet we know that december was remarkably a mild winter about most of the united states, and we also know that warm, moist surface air was a factor in friday fueling and making these tornadoes more powerful. it's not the only factor, but it was one of the factors. >> parts of the country have been seeing unseasonably warm, maybe even record setting temperatures. it feels more like spring or fall rather than mid december. talk to me about how this weather could have fueled these horrific storms in the heartland. >> one thing we have noticed, the studies are looking since 1979 over the past four decades