Here is some more information from the Desert Doppler 15 Monsoon Guide. (ABC 15 Weather)

Every year it seems we hear about some damage due to microbursts. These are vertical wind shears created by downburst winds. They are capable of producing a column of air with wind of over 150 miles per hour. These winds do not spiral like a tornado but are directed downward and then when they hit the ground spread out in all directions. They usually come after a thunderstorm. Luckily these do not happen very often. (More Information on downburst winds…)