A severe thunderstorm is when there is lightning and thunder. There is also a lot of precipitation. (precipitation is rain)
How Severe Thunderstorms Forms
A severe thunderstorm forms by cold and warm fronts all around the area. Also a severe thunderstorm has to include moisture in the air to make cumulus clouds. There has to be warm air that can rise quickly too. The wind can be 57.5 miles per hour or even faster, you also have lots of precipitation(rain). If the storm is really bad, it will form a tornado.
Examples Of Severe Thunderstorms
On June 13, 1991, about 40,000 golf fans gathered at Hazeltine, the National Golf Club in Chaska, Minnesota.
The people who gathered there was there to watch the U.S Open Championship. There was a quick big flash in the sky and everyone ran to the nearest building or their car. Six people went under a weeping willow tree that was 30 feet tall. They thought that it would be safe because there were taller trees near by, but obviously it was a big mistake because the lightning went to the tree. One of them was shortly paralyzed and the others were knocked out, one of the men's heart stopped beating, he died from cardiac arrest.( cardiac arrest is
a sudden, temporary function of the heart.) Another example is December 22, 1938 in Vatican City in Rome. People saw lightning go to St Peters Basilica, and it broke a lot of windows, no one was hurt though but they did have to fix the broken windows.