ightning: 
By definition, a thunderstorm has to contain lightning and thunder. Find out more about them with our Lightning lesson. 

lash Floods: 
Heavy rain from thunderstorms can produce flash floods. Find out more with our Flash Flood! lesson. 

ornadoes: 
Tornadoes are the most severe hazard a thunderstorm can produce. Find out more about them with our Tornado lesson. 

ownbursts: 
Downbursts are incredibly large and strong downdrafts that spread wind sideways when it hits the ground. The damage that is caused by downbursts is similar to, and often confused with tornado damage. 

There are two kinds of downbursts. Macrobursts can be up to 130 mph and cover a diameter of five miles. Microbursts are smaller than macrobursts, but just as deadly. Their winds can exceed over 160 mph and last only ten minutes. Because of their size, microbursts are often undetected and can be a serious problem for aircrafts because of wind shear. 

ail: 
Hail is precipitation in the form of odd-shaped icy lumps called hailstones. Hail falls from thunderstorms that contain strong updrafts and a large supply of supercooled water droplets. 

A hailstone forms when a small piece of ice is carried through portions of a cumulonimbus cloud that contain different concentrations of supercooled water droplets. As the ice pellets travel in and out of patches of water droplets, the water instantly freezes to it, forming layers of ice and increasing the hailstone's size. When it becomes too large and heavy to be supported by the updraft, the hailstone falls out of the cloud. 

Hailstones have been found in sizes ranging from pea size to baseball size. The largest hailstone in the US weighed 1.67 pounds and was 5.5 inches in diameter. Sometimes so much hail falls that plows are needed to clear it away!