This is a chilling, eerie map – it depicts all the tornado emergencies to ever be issued in the United States. Tornado emergencies are the most urgent, life-or-death alert that the National Weather Service can issue. In the past 27 years, there have only been 314 tornado emergencies issued. They're reserved only for anticipated catastrophic, high-end tornadoes – intense-to-violent EF3, EF4 and EF5 monsters on a crash-course with population centers. On April 27, 2011, there were 37 of them issued. THIRTY SEVEN. The tornado emergency was invented on May 3, 1999, when a mile-wide F5 tornado was barreling up the H. E. Bailey Turnpike into the Oklahoma City metro area. Forecasters knew that dozens would perish, and that entire neighborhoods would be obliterated. At the National Weather Service in nearby Norman on the University of Oklahoma campus, the warning meteorologist on duty felt a run-of-the-mill tornado warning wouldn't cut it. Their 6:57 p.m. message reflected it. The warning began “tornado emergency in south Oklahoma City,” the phrase “tornado emergency” never having been used before. The pioneered phrasing is now reserved only for the most significant events with the highest fatality potential, famously being issued on May 20, 2013, as another EF5 tornado barreled into Moore. (Joplin, Missouri SHOULD have been a tornado emergency, but infamously wasn't.) This tornado season, take ALL tornado warnings seriously – but, if you find yourself in a tornado emergency, know what it means. If you hear the phrase "tornado emergency," know that the decisions you make will be critical for survival.