Microbursts are down currents in the cloud which also move outwards by reaction from the ground, having speeds considerably in excess of 1000 feet per minute downwards (up to 6000 fpm) and 50 kt horizontally. The windshear (headwind to tailwind) may be between 50 and 90 kt.

They are largely caused by descending raindrops which cool the surrounding air by evaporation, the higher density accelerating the downdraught still further.

They are concentrated in a burst which is up to 4 km in horizontal length and have a lifetime of less than 5 minutes. A macroburst is a similar event but over a bigger area.

Microbursts are most likely to occur in summer air mass thunderstorms in low latitude regions where surface conditions are dry.

They cause extreme turbulence and severe windshear conditions. A warning sign of windshear is virga, which is streaks of precipitation from below the cloud which do not reach the ground.