The Storm Prediction Center (SPC), based out of Norman, Oklahoma, is responsible for issuing severe weather watches across the U.S. during storm events. But, they also issue outlooks on the likelihood of severe weather days in advance. According to the SPC, these are actually forecasts for the probability of a severe weather event, whether it be large hail, damaging winds, or a tornado.
Previously, the SPC outlooks were broken into 3 categories: slight risk, moderate risk, and high risk severe weather days. Back in October of 2014, two new categories were added to better communicate the risk of severe weather: marginal and enhanced. All five of these categories are designed to give the public preparation time for specific, weather-related risks that threaten their location.