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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.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.weatherquestions.com/What_causes_thunderstorms.htm

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

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 ...

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

Without thunderstorms and lightning, the earth-atmosphere electrical balance ... Rainfall from thunderstorms causes flash flooding, killing more people each year  ...

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 ...

www.answers.com/Q/What_causes_storms

In simple terms, storms can be caused by the meeting of very cold air with very warm air. A storm originates when a low pressure system is surrounded.

.ask.com/youtube?q=What+Causes+Storms%3F&v=CW_SKUtIRc0
Nov 8, 2013 ... The Philippines are hit by more than 20 tropical storms a year, says the BBC's Jay Wynne. At least three or four turn into typhoons. But why is ...