異常気象
According to the World Meteorological Organization (WMO), severe weather can be categorized into two groups: general severe weather and localized severe weather. Nor'easters, European wind storms, and the phenomena that accompany them form over wide geographic areas. These occurrences are classified as "general severe weather". Downbursts and tornadoes are more localized and therefore have a more limited geographic effect. These forms of weather are classified as "localized severe weather". The term "severe weather" is technically not the same phenomenon as extreme weather. Extreme weather describes unusual weather events that are at the extremes of the historical distribution for a given area.