Immediate, urgent situation requiring action, life-threatening, ongoing crime, fire, illegality, etc.
High: A situation that directly threatens life, bodily integrity, public interest, or property with a high risk.
Medium: "It would be good if you took action." "If I were you" level. E.g., you stopped in the wrong place.
Low: There is no risk yet, but it is possible, e.g., a car left overnight in a bad neighborhood.