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Causes

This graphic shows the conditions favorable for certain organized thunderstorm complexes, based upon CAPE and vertical wind shear values.

Organized severe weather occurs from the same conditions that generate ordinary thunderstorms: atmospheric moisture, lift (often from thermals), and instability.<ref name="SPC FAQ">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A wide variety of conditions cause severe weather. Several factors can convert thunderstorms into severe weather. For example, a pool of cold air aloft may aid in the development of large hail from an otherwise innocuous appearing thunderstorm. However, the most severe hail and tornadoes are produced by supercell thunderstorms, and the worst downbursts and derechos (straight-line winds) are produced by bow echoes. Both of these types of storms tend to form in environments high in wind shear.<ref name="SPC FAQ"/>

Floods, hurricanes, tornadoes, and thunderstorms are considered to be the most destructive weather-related natural disasters. Although these weather phenomena are all related to cumulonimbus clouds, they form and develop under different conditions and geographic locations. The relationship between these weather events and their formation requirements are used to develop models to predict the most frequent and possible locations. This information is used to notify affected areas and save lives.


Severe weather sections
Intro  Terminology  Causes  Categories  High winds  Hail  Heavy rainfall and flooding  Severe winter weather  Heat and drought  References  

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