So you can see that a sudden change of wind speed can change the airspeed and therefore, change the amount of lift keeping the airplane in the air. If the airplane is going slow, like on take off or landing, this can be very dangerous. Most of the Microburst incidents happen in a thunderstorm. As mentioned above, there are several other associated storms, but by far the thunderstorm causes the most Microburst activity. Virga is rain that evaporates before it reaches the ground and is associated with a dry Microburst.
Observations suggest that approximately five percent of all thunderstorms produce a microburst.
Downdrafts associated with Microbursts are typically only a few hundred to a few thousand feet across. When the downdraft reaches the ground, it spreads out horizontally and may form one or more horizontal vortex rings around the downdraft. The outflow is typically 6-12 thousand feet across and the vortex ring may rise 2 thousand feet above the ground. Here is a diagram of a Microburst this picture shows the Microburst coming straight down, which is a symmetric Microburst. As you all know thunderstorms are normally moving and the Microburst can have an uneven shape.