Can someone explain, using as many layman's terms as possible, what a tornado is and how it forms?

Question

I'm interested in Meteorology, but the Wikipedia article on the subject is hard to understand and doesn't do that great of a job explaining it to those who aren't familiar with weather-terms.

Answer 1

If you can get a copy of Donald Piston's book titled, "Meteorology" then you should get it and read it.  He explains most all cyclonic wind patterns and how they develop.  This is done with the physics of his time (this is about 1950) but I feel the rules still hold.  Many, many great facts are given and he even delves into the "current" climate change craze.  Absolutely wonderful book.  I think Amazon may have some used ones as it is out of print.  It is worth the read.

Answer 2

To expand on what Anthony said.

A rapidly spinning, horizontal column of air is shifted to a vertical position due to strong updraft in a thunderstorm.

Wind shear, which is a change in wind speed with height is responsible for creating the horizontal column.  

The updraft is due to a large difference in temperature between the air in the updraft and the surrounding air. So, imagine a warm pocket of air rising, since hot air rises, and surrounding this pocket of warm air is colder air.  As long as the air is colder, the pocket of warm air will rise.  The bigger the difference, the faster the pocket of warm air will rise.  

Thunderstorms that produce tornadoes usually have very strong updrafts and also very big values of wind shear or a large difference in wind speeds up through the atmosphere.  

So once the horizontal column is shifted vertically, it eventually lowers to the ground through the wall cloud.  This is the point where there are several unknowns, as to why it lowers and why some storms have tornadoes and others do not.  

I hope this helped somewhat. Use the link below for a thorough understanding of tornadoes.

Answer 3

I have used this description a couple of times on here. It is in my own words and I am pretty sure I simplified it well.

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Take an individual thunderstorm. This thunderstorm may be your run-of-the-mill thunderstorm or it may contain components that really juice it up to be extraordinary. Let's use baseball as an analogy, since I adore baseball. A typical thunderstorm is a solo homerun. Now, a solo homerun holds some value, but alone doesn't do a terrible amount of damage. Now, load the bases before that homerun and what will you have? A grand slam, and that does some serious damage. We'll say that a thunderstorm needs its "bases loaded" before becoming severe and possibly a tornadic threat.

An atmospheric condition that can begin to load a thunderstorm's bases is: developing ahead of a cold frontal boundary. Any thunderstorm can develop in an area of general instability with enough heat and moisture- that's a solo home run. But add a cold front into the mix and you have a man on first base. Thunderstorms form out ahead of cold fronts and they can be strong. You know the theory "warm air rises/ cold air sinks"? Picture that actually taking place- a cold front pushes into exceptionally warm (and moist) air with high dewpoints (which occurs ahead of a cold front due to the southerly winds that take place there), and the cold air actually DIGS its way through the warm air, plowing the warm air and making it rise at a faster, almost violent rate. Man, you get some big thunderstorms that way. This often accounts for those severe squall lines most of us experience occasionally, with hail and high winds. And rarely, one or more of these could be tornadic.

The man on second could be described as daytime heating. During max heating, which takes place in the late afternoon hours (after the sun has had a chance to pound on us all say), the extra heat really aids in severe thunderstorm development. So, the sunnier it is in the morning and during the early afternoon, the more of a chance of severe thunderstorms in the late afternoon/evening. Just picture warm air rising at a violent rate, which becomes your "updraft" I will refer to momentarily.

Now, we've talked about the occurences that aid a thunderstorm's lower half, but now it is time to address the upper half of the storm. This is your man on third. Figure that thunderstorms are 30,000-60,000 feet tall - with the severe ones more around the 60,000 ft height, sometimes even taller than that - so, you'd have to figure something must need to take place in the air up there to help make a thunderstorm severe or tornadic. You need some upper level dynamics: Dry air advection at around 10K feet, and the jet stream nearby (high winds aloft allow for extra divergence in the upper levels of the storm, which makes more room for the updrafts of warm moist air to continue coming from below), and these stronger winds aloft can force the updraft to tilt, thus turning the updraft vertical. Importantly, a change in wind direction with height creates turning within the storm. This twisting updraft will stretch, hence increasing its rotation speed (one meteorologist described this as an ice skater spinning faster when she pulls her hands in). This stretching, twisting updraft may touch the ground as the form of a tornado, or stay aloft as a funnel cloud.

As far as "Tornado Alley" goes, the bases are loaded with really big, scary guys with large mustaches and .350 batting averages. In other words, these same things happen in Tornado Alley, but they happen at an extreme, and more frequently (because there are always guys on base). Tornado Alley often has these atmospheric dynamics happening perfectly, and at the same time, because of the location being northwest of the Gulf of Mexico and just east of the Rocky Mountains.

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Hope this helps.

Answer 4

A tornado is a violent, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris.

Most tornadoes have wind speeds between 40 mph (64 km/h) and 110 mph (177 km/h), are approximately 250 feet (75 m) across, and travel a few miles (several kilometers) before dissipating. Some attain wind speeds of more than 300 mph (480 km/h), stretch more than a mile (1.6 km) across, and stay on the ground for dozens of miles (more than 100 km).[1][2][3]

Although tornadoes have been observed on every continent except Antarctica, most occur in the United States.[4] They also commonly occur in southern Canada, south-central and eastern Asia, east-central South America, Southern Africa, northwestern and southeast Europe, western and southeastern Australia, and New Zealand.[5]

As the mesocyclone approaches the ground, a visible condensation funnel appears to descend from the base of the storm, often from a rotating wall cloud. As the funnel descends, the RFD also reaches the ground, creating a gust front that can cause damage a good distance from the tornado. Usually, the funnel cloud becomes a tornado within minutes of the RFD reaching the ground.

Answer 5

A tornado, Spanish "to twist or turn", results from a cold air mass butting up against a warm air mass with the jet stream most likely steering the whole mess. It is a very localized event but can travel hundreds of miles undiminished. Winds can exceed 300mph.

How it forms is the crux of the problem. We can measure temperature, humidity, wind speeds and directions, pressure, etc. But we still don't know what triggers the formation of the initial vortex or vortices, thus we have a very limited ability to predict and warn people in sufficient time. But those storm chasers are still out there every season to keep looking for the answer.

Answer 6

A tornado is a rapidly rotating column of air produced when wind shear aloft creates a horizontal, spinning cylinder of air lifted toward the vertical due to a strong, persistent updraft.

Anthony