A tornado is a very small area of low pressure surrounded by powerful, rotating winds of up to 300 miles per hour. Its strength is measured by the Enhanced Fujita Scale, ranging from EF - 0 to EF - 5.

Many people used to believe that tornadoes were random, unpredictable events. Others believed that there must be some way to predict them in advance.

After a tornado struck an Air Force base in 1948, two officers studied weather conditions. Then, five days later, they were able to issue the first accurate tornado warning.

Before radar, meteorologists could issue tornado watches but couldn't know for sure that a tornado had formed until someone saw it. Radar, however, made it possible to see signs of a tornado on a weather map and issue warnings for people to take cover.

"Tornado Alley" is a large tornado-prone area in the central United States, including parts of Texas, Oklahoma, Kansas, Nebraska, South Dakota, Iowa, Missouri, and Arkansas.

Because it is not an official term, "Tornado Alley" does not have specific boundaries. This explains why many maps show it including different areas of many states.

To protect people from the area's frequent tornadoes, cities and towns in Tornado Alley enforce strict building codes. Many homes also have storm cellars or basements.

Since water covers about 70% of the earth, it should come as no surprise that tornadoes can form over water. These are called tornadic waterspouts.

Other waterspouts form when cool air moves over warm water; the air heats up rapidly and starts to rise. Then, nearby air begins to rotate at high speeds, and it finally becomes a fair-weather waterspout.

If people love snow and ice, then they might like to spend their winter vacation in the most wintry way possible - in an ice hotel!

An ice hotel is usually built using a snow-ice mixture called snice, which is extremely strong and good for insulation.

To build an ice hotel, builders first put up a steel frame. Then, the frame is filled in with a snow-ice mixture calls snice. After the steel frame is taken off, only a thick, sturdy, ice-walled building remains.

Many ice hotels are structured like traditional hotels, while others offer guests a chance to stay in their own individual igloos.

Many ice hotels offer amenities such as ice restaurants, churches, and meeting rooms - all carved from solid ice, of course. Even small details like the cups in the ice restaurant are made from small chunks of ice.

For years, the builders' hard work would melt every spring, so an ice hotel could only exist during the winter. Now, some ice hotels offer guests the option of staying in a permanent, heated structure.

Figure skating events were added to the Winter Olympics in 1908. Speed skating joined the lineup in 1924 for men and 1960 for women. Now, ice skating is a permanent fixture in the realm of winter activities.

Both modern and early versions of ice skates allowed skaters to travel quickly over ice, but unlike modern skates, these early versions weren't sharp enough to cut into the ice. Instead, they slipped along on top of it.

When ice skating became more popular, people found that they needed more places to skate.

For most of history, ice skating was limited to naturally formed bodies of frozen water (lakes, ponds, etc.). This kept people in cities from being able to skate - until creative Londoners invented the first artificial ice rink.