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TORNADO FAQs

Whenever and wherever conditions are right, tornadoes are possible, but they are most common in the central plains of North America, east of the Rocky Mountains and west of the Appalachian Mountains. They occur mostly during the spring and summer; the tornado season comes early in the south and later in the north because spring comes later in the year as one moves northward. They usually occur during the late afternoon and early evening. However, they have been known to occur in every state in the United States, on any day of the year, and at any hour. They also occur in many other parts of the world, including Australia, Europe, Africa, Asia, and South America. If you'd like to plot tornado tracks, download Severe Plot and the associated data from the NOAA Storm Prediction Center.

Yes, although some states have many more tornadoes than others.

We are not aware of any tornadoes occurring in the Arctic Circle. Tornadoes need moisture and warm air to form, which is unusual at that lattitude. Plus tornadoes or their evidence have to be observed by someone, and the Arctic Circle has few residents!

A gully could actually make a tornado more intense, just as an ice skater spins faster when he or she stands up tall and stretches their arms up straight over their heads. Every major river east of the Rockies has been crossed by a significant tornado, and high elevations in the Appalachians, Rockies, and Sierra Nevada have all experienced tornadoes. A violent tornado crossed the Continental Divide in Yellowstone National Park.

"Tornado Alley" is a 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!

About 1000

According to research done by Dr. Harold Brooks here at NSSL, the most common birthplace for a violent tornado (F4 or greater) is in south-central Oklahoma.

Check NSSL's Severe Weather Climatology page.

Tornado Climatology

Where and when do tornadoes occur?

Tornadoes occur in many parts of the world, including Australia, Europe, Africa, Asia, and South America. Even New Zealand reports about 20 tornadoes each year.

Two of the highest concentrations of tornadoes outside the U.S. are Argentina and Bangladesh. Both have similar topography with mountains helping catch low-level moisture from over Brazil (Argentina) or from the Indian Ocean (Bangladesh).

About 1,000 tornadoes hit the U.S. yearly. Since official tornado records only date back to 1950, we do not know the actual average number of tornadoes that occur each year. Plus, tornado spotting and reporting methods have changed a lot over the last several decades.

» More About TORNADO OCCURRENCE

Tornado season usually refers to the time of year where the U.S. sees the most tornadoes. The peak “tornado season” for the southern plains -- often referred to as Tornado Alley -- is during May into early June. On the Gulf coast, it is earlier during the spring. In the northern plains and upper Midwest, tornado season is in June or July. But, remember, tornadoes can happen at any time of year. Tornadoes can also happen at any time of day, but most tornadoes occur between 4-9 p.m.

Map of the US showinf tornado alley covering parts of Texas, Oklahoma, Kansas, Nebraska, N. Dakota, Iowa, and Minnesota
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Tornado Alley is a nickname for an area that consistently experiences a high frequency of tornadoes each year. The area that has the most strong and violent tornadoes includes eastern SD, NE, KS, OK. Northern TX, and eastern Colorado. The relatively flat land in the Great Plains allows cold dry polar air from Canada to meet warm moist tropical air from the Gulf of Mexico. A large number of tornadoes form when these two air masses meet, along a phenomenon known as a "dryline."

The dryline is a boundary separating hot, dry air to the west from warm, moist air to the east. You can see it on a weather map by looking for sharp changes in dew point temperatures. Between adjacent weather stations the differences in dew point can vary by as much as 40 degrees or more. The dryline is usually found along the western high plains. Air moving down the eastern slopes of the Rockies warms and dries as it sinks onto the plains, creating a hot, dry, cloud-free zone. During the day, it moves eastward mixing up the warm moist air ahead of it. If there is enough moisture and instability in the warm air, severe storms can form - because the dryline is the "push" the air needs to start moving up! During the evening, the dryline "retreats" and drifts back to the west. The next day the cycle can start all over again, until a larger weather system pushes through and washes it away.

Tornadoes kill an average of 60 people per year, mostly from flying or falling debris.

The Tri-State Tornado of March 18, 1925 was the deadliest tornado in history, killing 695 people. It is also the longest tornado track ever known - 219 miles - across parts of Missouri, Illinois and Indiana.

Codell, KS was struck by a tornado on May 20 three years in a row: 1916, 1917, and 1918.

Understanding the threat posed by tornadoes in the United States - particularly the threat of strong and violent tornadoes - is valuable knowledge to everyone, but especially to weather forecasters and emergency management people. Knowledge about long-term patterns helps us be better prepared for natural disasters and could also help scientists detect shifting patterns in severe weather events caused by climate change.

HOW DOES NSSL CONTRIBUTE?

Dryline Studies
NSSL researchers combine data collected during a 1991 field experiment with current model data to study factors influencing the location and timing of storm initiation.

Severe Thunderstorm Climatology
An NSSL scientist compiled data from past weather events into a graphical probabilistic data base showing the annual threat of severe thunderstorms occurring in the US. For this aignificant accomplishment Harold Brooks received a Department of Commerce Silver Medal award.

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