Jetstream (IMAGE) Northern Illinois University Caption Weather patterns that sparked the US tornado outbreak in late May 2019 began thousands of miles away with thunderstorms over the Maritime continent. Credit Credit: Northern Illinois University 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.