Supercell (IMAGE) American Geophysical Union Caption A supercell storm, known to produce violent tornadoes, forms in Courtney, Oklahoma in April 2014. A new study shows that peak tornado activity is occurring nearly two weeks earlier in Oklahoma, Kansas, and northern Texas, according to a new study published in Geophysical Research Letters. Credit Credit: Kelly DeLay/Flickr Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.