The first round of severe weather in a forecasted double-header threat is approaching west Alabama as Friday night becomes Saturday morning and the system has already created tornadoes in several US states.

Most of the rest of north Alabama will have a Level 2 risk, and a small area in the northeast corner of the state will have a Level 1 risk. If storms can develop they have the potential to be intense, especially west of Interstate 65. Tornadoes, damaging winds and hail will be possible.

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?