Extreme or severe weather is simply really bad weather or
weather on a larger, more serious and devastating scale.

or example:

Instead of a few snowflakes falling, there is a snowstorm and snow drifts can be many meters deep.
Extreme forms of a windy day include gales, hurricanes, and tornadoes.
Heavy rain may last much longer than a few hours or even days and result in flooding of rivers, roads, and homes.

Extreme weather events may not happen very often. When they do they can cause destruction of buildings, vehicles, roads, and homes, costing many billions of pounds. People’s lives are also at risk from some unexpected weather events. Modern technology allows predictions to be made so people know when and where a hurricane is going to hit land. However, some storms, including tornadoes, still cannot be forecast accurately.

Click on any of the severe weather events right to find out more information about them, see pictures and read about examples.