The document discusses microbursts, powerful downdrafts that can occur during thunderstorms. It explains that microbursts are caused when rain-cooled air accelerates downward and hits the ground, then spreads out in all directions. The document outlines that there are two main types of microbursts - dry microbursts, which do not involve precipitation, and wet microbursts, which contain heavy precipitation, and that wet microbursts can be more dangerous due to the additional hazard of rain, hail or snow.