A severe weather outbreak is expected on Saturday in Alabama, according to the National Weather Service. NOAA’s Storm Prediction Center has added -- and now expanded as of Thursday afternoon -- a rarely-used Level 4 out of 5 risk for parts of a large part of Alabama for Saturday.

It marks only the third time since at least 2006 that the highest risk level has been issued the day before an expected outbreak.

We all hear the terms when there's a threat of severe weather. But what does each alert mean, and how does it affect you?