Microburst dumps rain and wind over Phoenix

A microburst has been filmed blasting a dangerous torrent of rain, hail and wind down from the sky in Phoenix.

Helicopter pilot Jerry Ferguson, who was filming the rolling thunderstorms for a TV report earlier this week, snapped an incredible picture of the weather phenomenon, the Washington Post reports.

Microbursts occur when a rush of cool wind shoots down out of a thunderstorm and crashes to the ground.

Once grounded, the winds splinter off in all directions and can reach speeds of up to 240km/h.

Microbursts are a major hazard for planes taking off and landing at airports.

Microbursts are triggered by two main physical processes - the drag created by falling rain and hail and evaporation.

Evaporating water cools the air, making it more dense and accelerating the descent.