A severe weather watch is issued when the risk of hazardous weather has increased significantly. The type of weather being advised for could happen at any point in time during the watch period. The hazardous weather is possible. It is intended to give a lead time so that emergency plans can be put into action.
A warning is issued when hazardous weather is occurring, imminent, or likely during that time. It means that the weather poses a threat to life and property. People in the path of a warned storm need to take protective action.
An advisory is issued when hazardous weather is occurring, imminent, or likely. This is for less serious conditions than a warning but means that significant weather will be happening.