Tornadoes for Middle School Science

Feb 20

4 min read

Tornadoes are one type of extreme weather. They happen when cold air gets on top of warm air. The falling cold air and the rising warm air can lead to violently rotating columns of air. Tornadoes happen on every continent except Antarctica, but they are most common in the United States.

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Tornadoes

Tornadoes are violently rotating columns of air that stretch from the ground to the clouds of a thunderstorm. They happen all over the world, on every continent except Antarctica, but they are most common in the United States. The United States hosts over 1,000 tornadoes per year, while Canada, in second place, has fewer than 100.

Most of the tornadoes in the United States happen in Tornado Alley, a broad strip of land including northern Texas, eastern Colorado, Oklahoma, Kansas, and Nebraska. Tornadoes are common in Tornado Alley because this is where the warm, moist air from the Gulf of Mexico meets the cool, dry polar air that comes down from Canada during the spring and summer months

The Rocky Mountains mean that cold air is sitting on top of warm moist air. The rising warm air and falling cool air meet the fast-moving air currents of the jet stream, and the air becomes turbulent. As the warm air rises in updrafts, the large number of water molecules within it condense and form thunderclouds. The heat energy released by the condensing water vapor makes the updrafts even stronger and the thunderstorm bigger.

The updrafts of the rising air and the downdrafts of the cool air sinking cause the winds inside the thunderstorm to rotate. If the updrafts are powerful enough, they can tilt the horizontal rotating wind up so that it revolves around a vertical axis. This mass of spinning air within a thunderstorm is called a mesocyclone. Most mesocyclones do not lead to tornadoes, and scientists don't yet know what determines if a tornado will or will not form.

As a tornado forms, the strong updrafts around the mesocyclone mean air can't get inside the center of the rotating winds. Fewer air molecules inside the mesocyclone create low pressure inside and high pressure outside of it. The difference in pressure causes a condensation funnel, often called the funnel cloud, to form. The condensation funnel is a tapered column of spinning water droplets that extends down from the thunderstorm. As it reaches for the ground, it mixes with dust and debris from the surface of the Earth. Scientists do not consider a rotating storm a tornado until the condensation funnel reaches the ground.

Tornadoes vary in intensity from weak with wind speeds between 65 and 110 miles per hour to extremely violent with wind speeds greater than 200 miles per hour. The weakest tornadoes last only a few minutes while the strongest tornadoes can last for hours. In 1971, a Japanese-American meteorologist named T. Theodore Fujita developed the Fujita Scale to measure the intensity of tornadoes.

Unlike hurricanes, the winds in a tornado are too intense to be measured, so the Fujita Scale classifies tornadoes based on the amount of damage they cause. Since tornadoes cause different amounts of damage depending on where they land, the system isn't always accurate at describing the intensity of a tornado. The Fujita Scale was updated in 2007 to include more precise indicators, and it is now known as the EF Scale for Enhanced Fujita Scale.

On the EF Scale, the weakest tornadoes are classified as EF0 with wind speeds between 65 and 85 miles per hour. The strongest tornadoes are EF5, with wind speeds over 200 miles per hour. The strongest tornado measured using the EF scale had winds over 300 miles per hour. Luckily, most tornadoes in the United States are classified as EF0 or EF1. Around 35% of tornadoes are EF2 or EF3, and only 2% are EF4 or EF5. Unsurprisingly, the strongest tornadoes cause the vast majority of tornado-related deaths.

Meteorologists have been able to decrease the number of deaths caused by tornadoes by setting up early warning systems. By monitoring the conditions in the sky, meteorologists can see if a tornado might develop. If this happens, they issue a tornado watch, which alerts people living in the area to get to a safe place. If a tornado is spotted, meteorologists issue a tornado warning, which means people need to find shelter immediately. Since the tornado watch and warning systems were put in place in 1953, thousands of lives have been saved from tornadoes.

Tornadoes are dangerous because their powerful winds tear apart buildings and whip debris through the air. People can be hurt by collapsing structures, being hit by debris, or being dragged along the ground by the high winds. The best place to be during a tornado is in a basement or an interior room of a building. If you are stuck outside during a tornado, meteorologists recommend taking shelter in a ditch and holding tight to something solid like a tree stump.

So far, we have described supercell tornadoes. These tornadoes form from a supercell, which is a giant thunderstorm with a mesocyclone. There are also non-supercell tornadoes. Non-supercell tornadoes are created by rotating wind at the Earth's surface. They move from the ground up and are generally not as powerful as supercell tornadoes.

All tornadoes end when the temperature differences around them end, there is no moisture left in the air, or the air around them becomes more stable. Until these things happen, there is nothing we can do to stop a tornado, which is why scientists want to study them, so we can learn how to keep people safe from these deadly storms.