Defining High-Impact Weather—or Not?

In a case several years ago, a Justice of the U.S. Supreme Court was famously quoted as saying “I can't define pornography, but I know it when I see it”. Something similar might be said about defining high-impact weather: it is difficult to define, but most of us recognize it when it occurs. This paper explores the many dimensions and characteristics of high-impact weather that simultaneously make it difficult to define and yet easily recognizable.