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The action of warm air rising and cold air sinking (convection) plays a key role in the formation of severe thunderstorms. If the warm surface air is forced to rise, it will continue to rise, because it is less dense than the surrounding air.
Two of the most important ingredients for thunderstorm formation are instability (unstable air) and moisture.

en.wikipedia.org/wiki/Storm

A storm is any disturbed state of an environment or astronomical body's atmosphere especially ... High wind is also the cause of sandstorms in dry climates.

www.weatherquestions.com/What_causes_thunderstorms.htm

Nov 28, 2010 ... Brief, simplified description of what causes thunderstorms.

pmm.nasa.gov/education/content/what-causes-thunderstorms

Thunderstorms form when an air mass becomes unstable (when air in the lowest ... making it warmer than its environment, which causes it to rise even farther.

www.weatherwizkids.com/weather-thunderstorms.htm

A thunderstorm is a storm with lightning and thunder. ... Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud.

www.reference.com/science/causes-storms-1bc6db6f4066aa04

Storms are formed when the movement of cold and warm air currents creates extreme ... is created at an atmospheric level as warm wet air rushes, causing cold.

www.nssl.noaa.gov/education/svrwx101/thunderstorms

Many hazardous weather events are associated with thunderstorms. Under the right conditions, rainfall from thunderstorms causes flash flooding, killing more ...

phys.org/news/2006-08-scientists-abrupt-storms.html

Aug 15, 2006 ... No two rain storms are alike. Dark clouds may form slowly throughout the day before a drop of rain falls, and sunny days can suddenly ...

www.stormsurf.com/page2/tutorials/weatherbasics.shtml

When the warm air is forced up, it causes surface air pressure to drop, sort of like ... In the north hemisphere, wind rotates counter-clockwise around a storm ...

eo.ucar.edu/kids/dangerwx/tstorm4.htm

Orographic thunderstorms are caused by air that is forced up by a mountain or hillside. Air mass thunderstorms are the result of localized convection in an ...