a type of localized downdraft, often associated with thunderstorms, producing very strong, short-lived wind shears
See microburst in American Heritage Dictionary 4
(mīˈkrō-bûrstˌ)
noun
A sudden, violent downdraft of air over a small area. Microbursts are difficult to detect and predict with standard weather instruments and are especially hazardous to airplanes during landing or takeoff.