What is Tornado Alley?

Tornadoes are a fascinating force of nature, as awe-inspiring as they are destructive. They form periodically due to the convergence of weather patterns, and often leave plenty of devastation in their wake. And for those who live in the active tornado regions of the world, they are an unfortunate fact of life.

Such is the nature of life for those who live in the infamous “Tornado Alley”, a region that extends from the southern US into parts of Canada. This area is so-named because of the frequency with which tornadoes take place. Compared to other active regions of the world, this area experiences the highest frequency of violent tornadoes.

Origin of the Name:

The term “Tornado Alley” was first used in 1952 as the title of a research project about severe weather in the US. This project was conducted by U.S. Air Force meteorologists Maj. Ernest J. Fawbush and Capt. Robert C. Miller, and covered a region extending from areas of Texas to locations throughout the mid-western US.

Tornado at Union City, Oklahoma Credit, NOAA Photo Library
Tornado at Union City, Oklahoma. Credit: NOAA Photo Library

The term has since caught on thanks to media sources as well meteorologist and climatologists, though many use the term “Great Plains Tornado Belt” as well.

Geographical Area:

The geographical boundaries of “Tornado Alley” have never been very clearly defined and no official definition has been adopted by the National Weather Service (NWS). As a result, different definitions and boundaries have been adopted based on different sets of criteria. For instance, the National Severe Storms Laboratory (NSSL) states:

“‘Tornado Alley’ is just a nickname made up by the media for an area of relatively high tornado occurrence; it is not a clearly defined area. Is tornado alley the area with the most violent tornadoes, or is it the area with the most tornado-related deaths, or the highest frequency or tornadoes? It depends on what kind of information you want!”

While no region of the US is entirely free of tornadoes, they occur more frequently in the mid-western US – spanning areas of Texas to parts of Oklahoma, Kansas, South Dakota, Iowa, Illinois, Missouri, New Mexico, Colorado, North Dakota, and Minnesota.

Tornado Alley
Artist’s impression of the geographical region known as “Tornado Alley”. Credit: Dan Craggs/Wikipedia Commons

Texas reports the most tornadoes of any state, whereas Kansas and Oklahoma rank first and second respectively in the number of tornadoes per area. Florida also reports a high number and density of tornado occurrences, though tornadoes there rarely reach the strength of those that sometimes occur in the southern plains.

However, the Canadian prairies, eastern Colorado and western Pennsylvania are often included in the boundaries. And last, several smaller areas have been designated as being their own “Tornado Alley” – which include the Texas/Oklahoma/Kansas core, the Upper Midwest, the lower Ohio Valley, the Tennessee Valley and the lower Mississippi valley.

There is also the term “Dixie Alley”, a name coined by Allen Peasons, a former director of the National Severe Storms Forecasting Center (NSSFC), in 1971. This name refers to the lower Mississippi Valley and upper Tennessee Valley were tornadoes occur frequently.

Nevertheless, most definitions focus on the geographical region known as the Great Plains where no major mountain ranges are located. This is important because mountains act as breaks on weather systems, forcing them to dump the majority of their moisture before crossing over them (the reason why the southwestern US has a more arid climate).

 Image from Federal Emergency Management Agency, a United States government agency, booklet FEMA 320 Third Edition, Section 1, Figure 1.1, page 3, titled Taking Shelter from the Storm: Building a Safe Room Inside your House. Credit: FEMA
Image from Federal Emergency Management Agency booklet, “Taking Shelter from the Storm: Building a Safe Room Inside your House” (3rd ed.). Credit: FEMA

In the case of the Great Plains, the region’s lack of these natural barriers leaves it open to cold fronts from Canada and warm fronts from Mexico and the Gulf Coast. When cold and warm front collide, they create supercells and thunderstorm systems that lead to tornadoes.

Impact:

Due to the frequency of tornadoes in certain areas of the United States, building codes and warning systems have been implemented. These include the institution of special building codes, construction of storm cellars, sirens, preparedness drills, education programs, and regular weather coverage by local media outlets.

According to the National Climatic Data Center, during the period of 1991 to 2010, those states that have the most experienced an average of 5.7 (Minnesota) to 12.2 (Florida) tornadoes. Using a long-term average (based on data collected between 1950 and 2012), the entire “Alley” experiences about 268 tornadoes per year.

In the southeastern United States, where housing is less robust and many people live in mobile homes, causalities are particularly high. According to the NOAA, almost 3600 tornadoes have occurred in the United States, which resulted in more than 20,000 deaths, between 1680 and 2000.

The track of the tornado that struck Moore, Oklahoma on May 20, 2013 is visible from space in this false color image taken on June 2, 2013 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite.
The track of the tornado that struck Moore, Oklahoma on May 20, 2013 is visible from space in this false color image taken on June 2, 2013 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite.

Meanwhile, data from the Tornado History Project shows there were 5,587 confirmed fatalities blamed on tornadoes across the United States between 1950 and 2012. Of those, 1,110 occurred in Tornado Alley. The injuries caused by tornadoes are much higher, with a reported 64,054 injuries being attributed to tornadoes during the same period – over 15,000 of which occurred in Tornado Alley.

The worst year on record was 2011, when tornado activity spiked leading to 1,704 confirmed tornadoes and 553 confirmed deaths. This includes the 158 deaths that resulted from the tornado that struck Joplin, Missouri, on May 22nd, which was also the deadliest since modern record-keeping began in 1950.

In financial terms, the cost of tornadoes is also quite high. In fact, the Insurance Information Institute reports that between 1993 and 2012, the average insured loss per year was $7.78 billion for severe thunderstorm events, including tornadoes. In 2011, during the spike in storms, an estimated $27 billion was filed for in insurance claims.

No matter how you slice it, living in regions where tornadoes are known to frequent is both a dangerous and expensive prospect. As our understanding of tornadoes grows, we are able to predict where they will form and what paths they will take with greater accuracy. As such, we can reduce the cost in human and monetary terms over time.

Deadly Tornado Rips Across Indiana and Kentucky
Satellite image showing the after-effects of the deadly tornado that ripped through Indiana and Kentucky. Credit: NASA Landsat Project Science Office and USGS EROS

But in the long run, the greatest safeguards against injuries and death are public awareness and education. Tornadoes are also an important aspect of Climate Change, since changes in our environment are likely to effect and exacerbate extreme weather patterns.

We have written many articles about tornadoes for Universe Today. Here’s How Do Tornadoes Form?, What was the Largest Tornado Ever Recorded?, New Gigantic Tornado Spotted on Mars, and Huge “Tornado” on the Sun.

If you’d like more info on tornado, check out the National Oceanic and Atmospheric Administration Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:

How Do Tornadoes Form?

Tornado in Kansas

How do tornadoes form? That is pretty easy to answer since there has been a large amount of study into the subject. They are usually the extreme result of a supercell thunderstorm. During the storm cold air and warm air combine in a set pattern: the cold air drops as the warm air rises. The warm air eventually twists into a spiral and forms the funnel cloud that we all associate with a tornado.

The formation of a tornado follows a clear set of steps. First there a change in wind direction and an increase in wind speed. This change occurs at an increasing altitude and creates an invisible horizontal spinning effect in the lower atmosphere. Next, rising air within the thunderstorm’s updraft tilts the rotating air from horizontal to vertical. Third, an area of rotation, 3-10 km wide is contained within a vast majority of the storm. This is where the strongest tornadoes form. Then a lower cloud base in the center of the storm becomes a rotating wall cloud. This area can be nearly rain-free. Lastly, a tornado develops and starts to wreak its destruction.

Once a tornado has formed, it follows a predictable life cycle. First, the mesocyclone(rotating air), along with the rear flank downdraft( RFD), starts moving towards the ground. A small funnel appears to build up at the bottom of a wall cloud. As the RFD reaches the ground, the surrounding dirt rises up, causing damage even to heavy objects. The funnel touches the ground immediately after the RFD, forming a tornado.

During the next stage the tornado’s main source of energy, the RFD, begins to cool. The distance the tornado covers, depends on the rate at which the RFD cools. If the RFD cannot further provide any more warm air to the tornado, it begins to die.

Lastly, with the tornado’s warm air supply cut, the vortex begins to weaken and shrivel away. As the tornado weakens, the mesocyclone also starts to dissipate, but a new mesocyclone can start very close to the dying one. Those are the basics of tornado formation and life.

We have written many articles about tornado for Universe Today. Here’s an article about the biggest tornado, and here’s an article about the Tornado Alley.

If you’d like more info on tornado, check out the National Oceanic and Atmospheric Administration Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Where are Tornadoes likely to Occur

Tornado at Union City, Oklahoma Credit, NOAA Photo Library

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Everyone knows about tornadoes. You may have seen them in movies or heard about them in the news. However one of the most important facts for a person to know is where Tornadoes are likely to occur. This makes simple sense. If you want to avoid hurricanes you know that you should likely not live in the Gulf Coast or Florida. If you want to avoid the chance of mudslides you wouldn’t live in Oregon. Knowing where and how tornadoes can appear can help you stay safer and better prepared in case such a storm happens.

For the most part we know that Tornadoes as they are known in the United States are largely a North American phenomenon. The unique position and composition of North America’s topography gives thunderstorms enough space, time, and energy to form tornadoes. The traditional red zone for tornadoes is the Great Plains region of the United States called Tornado Alley. This region is known for spawning several tornadoes a year and in this region tracking storms and preparing for tornadoes is a way of life. The flat grasslands are perfect place for pressure systems to collide, creating powerful storms and in turn powerful tornadoes.

Interesting enough Tornado Alley is not the only area where tornadoes can happen. Tornadoes can occur anywhere in continental United States if the conditions for tornado formation are met. That means if you have a particularly strong thunderstorm system in your area with high winds there is a strong possibility of a Tornado happening.

The frequency of tornadoes happening outside the Tornado alley have increased with powerful storms ripping up areas that would be by conventional wisdom considered safe such as the Southeast or the Atlantic Seaboard.

One type of location that is generally safe from Tornadoes is the city. However recent events have proven that not likely doesn’t mean never. Two years ago a powerful tornado ripped through downtown Atlanta and doing major damage to the CNN headquarters. The other major tornado in a major city happened recently in New York City. A twister touched down in the Bronx in September of this year in the early morning hours also did serious property damage.

The danger of tornadoes in unlikely locations is that they are harder to spot. The tornado that struck Piedmont, Alabama became one of the deadliest on record because the area was hilly and full of trees. This made it impossible for residents to see the storm funnel approaching. This is why it is important for local news to have good weather tracking systems to properly warn residents in case of unusual weather conditions.

We have written many articles about tornadoes for Universe Today. Here’s an article about the Tornado Alley, and here’s an article about how tornadoes are formed.

If you’d like more info on tornadoes, check out the National Oceanic & Atmospheric Administration (NOAA) Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

What Are Tornadoes?

Tornado at Union City, Oklahoma Credit: NOAA Photo Library

Also known as a twister, a tornado is a rotating column of air that can cause a tremendous amount of damage on the ground. Tornadoes can very in size from harmless dust devils to devastating twisters with wind speeds greater than 450 km/h.

A tornado looks like a swirling funnel of cloud that stretches from bottom of the clouds down to the ground. Depending on the power of the tornado, there might be a swirling cloud of debris down at the ground, where it’s tearing stuff up. Some tornadoes can look like thin white ropes that stretch from the sky down to the ground, and only destroy a thin patch of ground. Others can be very wide, as much as 4 km across, and leave a trail of destruction for hundreds of kilometers.

Tornadoes appear out of special thunderstorms known as supercells. They contain a region of organized rotation in the atmosphere a few kilometers across. Rainfall within the storm can drag down an area of this rotating atmosphere, to bring it closer to the ground. As it approaches the ground, conservation of momentum causes the wind speed to increase until it’s rotating quickly – this is when tornadoes cause the most damage. After a while the tornado’s source of warm air is choked off, and it dissipates.

When a tornado forms over water, it’s called a waterspout. These can be quite common in the Florida Keys and the northern Adriatic Sea. Most are harmless, like dust devils, but powerful waterspouts can be driven by thunderstorms and be quite dangerous.

Scientists have several scales for measuring the strength and speed of tornadoes. The most well known is the Fujita scale, which ranks tornadoes by the amount of damage they do. A F0 tornado damages trees, but that’s about it, while the most powerful F5 tornado can tear buildings off their foundations. Another scale is known as the TORRO scale, which ranges from T0 to T11. In the United States, 80% of tornadoes are F0, and only 1% are the more violent F4 or F5 twisters.

Although they can form anywhere in the world, tornadoes are mostly found in North America, in a region called Tornado Alley. The United States has the most tornadoes of any country in the world; 4 times as many as the entire continent of Europe. The country gets about 1,200 tornadoes a year.

We have written many articles about the tornado for Universe Today. Here’s an article about the biggest tornado, and here’s an article about how tornadoes are formed.

If you’d like more info on tornadoes, check out the National Oceanic & Atmospheric Administration (NOAA) Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.