What is extreme weather?

Extreme climate: When there is a statistical small probability weather and climate "anomaly" phenomenon in a certain place, or the weather and climate in a certain place seriously deviates from its average state, it means that there is an "extreme climate". According to the regulations of the World Meteorological Organization, if the hourly, daily, monthly and annual values of a climate element reach more than 25 years, or the "difference" of the corresponding 30-year average exceeds twice the mean square deviation, then the climate element is an "abnormal" climate value. A climate with an "abnormal" climate value is called an "extreme climate". Drought, flood, high-temperature heat wave and low-temperature chilling injury can all be regarded as extreme climate.

Extreme weather event: it is a rare weather event in a specific area and at a specific time (within one year). There are many definitions of "rare", and the rarity of extreme weather events is generally equivalent to the observed probability density function being less than 10 or 90th percentile. Extreme weather characteristics vary from region to region. A single extreme event cannot be directly attributed to man-made climate change, because extreme events may occur naturally. When an extreme weather form lasts for a certain time, such as a season, it can be classified as an extreme weather event, especially when the event produces an average extreme value or a total extreme value (such as drought or rainstorm in a season).

(Quoted from China Climate Change Network)