Extreme weather includes weather phenomena that are at the extremes of the historical distribution, especially severe or unseasonal weather. The most commonly used definition of extreme weather is based on an event's climatological distribution. Extreme weather occurs only 5% or less of the time. According to climate scientists and meteorological researchers, extreme weather events are rare.

According to the National Oceanic and Atmospheric Administration, there were a record twelve weather disasters costing more than $1 billion in 2011. The previous record was nine in 2008.