Severe storms happen in low-pressure weather systems. Warm,
wet air begins rising into the air. The higher it rises, the cooler
it becomes. Water vapor in the air forms drops, a process called
condensation. The drops join together to form clouds, and then
precipitation of some kind (rain, sleet, snow, or hail) will fall
down to Earth’s surface.
Although conditions must be very specifi c for a thunderstorm
to develop, thunderstorms remain the most common kind of
extreme weather. Before a thunderstorm can develop, there have
to be three conditions present: the air has to be full of moisture, there must be either an intensely
heated portion of Earth’s surface sending warm air up quickly or an approaching cold front, and the
warm air that is rising must be warm enough to stay warmer than the air it passes through as it rises.
The moisture in the rising air condenses, clouds form and a storm begins.
A cold front happens when cold air is moving near the surface of Earth, and it pushes warm air
up very quickly. This is often the beginning of a thunderstorm. Clouds form, and heavy rains begin
falling. Opposite electrical charges inside storm clouds separate, causing lightning to fl ash towards
Earth. Lightning has enough energy to heat the air all around it. This sudden burst of heat is what
causes the noise we know as thunder. Thunderstorms often bring disasters with them, including
fl oods, fi res caused by lightning, damage from hailstones or strong winds, and even tornadoes. A
tornado is a spinning mass of air over land that can destroy virtually everything in its path.
A blizzard is a combination of strong winds and extremely low temperatures. Snowfall increases
until it is so heavy it is diffi cult or impossible to see. People can become lost in the snow and freeze to
death. Homes can be covered over with snow, trapping people indoors.
A hurricane is the most powerful storm known on Earth. Forming over warm ocean waters off the
coast of the tropics, they can become gigantic swirling mixtures of air and water between 100 and
900 miles wide. Wind speeds can average about 75 miles per hour. Hurricanes do the worst damage
to coastal cities because they quickly lose their strength when they move over land. Hurricanes are so
large and powerful that their swirling clouds can be seen from space.
Organizations like FEMA (the Federal Emergency Management Agency) and the American Red
Cross help victims of severe weather to deal with its aftermath.