When do tornadoes strike

Tornadoes can be strong enough to destroy large buildings or lift ton railroad cars from the tracks. A tornado might not have a visible funnel until it picks up debris from the ground. The strength of a tornado is measured by the Enhanced Fujita Scale continue scrolling for information on the Enhanced Fujita Scale. The truth is that scientists don't fully understand how tornadoes form.

A parent supercell thunderstorm is needed. Beyond that, each storm is different. Some research suggests it has to do with how strongly the wind changes direction with height or how much moisture is in the air. Other research suggests it forms because of the difference between the temperature of the surrounding air and the temperature of the cold downdrafts coming from the storm. A supercell is an organized thunderstorm that contains a very strong, rotating updraft.

This rotation helps to produce severe weather events such as large hail, strong downbursts and tornadoes. Supercells usually form isolated from other thunderstorms because it allows the storm more energy and moisture. These storms are relatively rare, but always a threat to life and property. A tornado begins as a rotating, funnel-shaped cloud extending from a thunderstorm cloud base, which meteorologists call a funnel cloud.

A funnel cloud is made visible by cloud droplets, however, if the cloud lacks moistrue, it may appear to be invisible. A funnel cloud does not affect the ground. If the funnel extends far enough down to begin affecting the ground, then it becomes a tornado. Tornadoes form under a certain set of weather conditions in which three very different types of air come together in a certain way.

Near the ground lies a layer of warm and humid air, along with strong south winds. Colder air and strong west or southwest winds lie in the upper atmosphere. Temperature and moisture differences between the surface and the upper levels create what is called instability , a necessary ingredient for tornado formation.

The change in wind speed and direction with height is known as wind shear. This wind shear is linked to the eventual development of rotation from which a tornado may form. A third layer of hot dry air becomes established between the warm moist air at low levels and the cool dry air aloft.

This hot layer acts as a cap and allows the warm air underneath to warm further, making the air even more unstable. Things start to happen when a storm system aloft moves east and begins to lift the various layers. Through this lifting process the cap is removed, thereby setting the stage for explosive thunderstorm development as strong updrafts develop. Complex interactions between the updraft and the surrounding winds may cause the updraft to begin rotating-and a tornado is born.

Most tornadoes occur east of the Rocky Mountains in a region known as "Tornado Alley. Often, the most dangerous tornadoes occur in the deep South and Southeast, where low visibility because of trees and hills lead to a false sense of security during severe weather outbreaks.

Furthermore, the South and Southeast tends to be more heavily populated than the Plains states. This region has been given the nickname "Dixie Alley. Peak months of tornado activity in the U. Although they are possible any time of the day or night, tornadoes tend to occur in the late afternoon and early evening hours, when the atmospheric conditions are most ripe for supercell thunderstorms.

They are most common from 4pm to 9pm. Tornado Alley is so active with severe storms because of its unique location. Tornado Alley is a nickname given to the plains region of the U. With the Rocky Mountains to the west, and the warm waters of the Gulf of Mexico to the south, this region is in a ripe location to produce supercell thunderstorms.

Midlatitude cyclones, like the one illustrated above with the red "L" and fronts, are the large-scale phenomena that spawn storms that create tornadoes. As midlatitude cyclones move eastward off the Rockies, they can tap into the warm, humid air from the Gulf of Mexico.

Therefore, tornado frequencies are lower in Europe than in North America. Nevertheless, a mid-latitude location, a high population density, and sophisticated detection abilities ensure that reported sightings of tornadoes are fairly high.

Central and northern Asia report few tornadoes, but part of this may be due to underreporting in the vast, less populated areas. Few tornadoes are known to occur over open seas because surface heating is far less intense over oceans than over land. The apparent lack of tornadoes is partly due to a lack of radar coverage over the oceans to detect them. Regions covered by sophisticated detection systems, such as the U.

The lowlands of mid-latitude South America and Africa also have some tornadoes. Recall that the maps showing lightning indicated thunderstorms here. The high frequency of tornadoes in south Asia and parts of Australia is largely attributable to their proximity to a supply of warm, moist air.

These areas also showed a high density of activity on the lightning-strike map. This graph shows the average frequency of tornadoes versus time of day, using data for St. How is it that a violent whirlwind can form in a cloud and then reach to the ground and make splinters and chaos of everything in its path?

On average, the U. A ten-state area of the Midwest has been named "Tornado Alley" in recognition of its attractiveness to tornadoes. However, tornadoes can occur in any state. In , Alabama was struck particularly hard, with tornadoes rated EF-5 the most intense on the Enhanced Fujita scale hitting Hacklesburg and Birmingham.

Imagery from GOES enabled weather forecasters to foresee the trouble that was about to hit Alabama. Click image for animation. With most weather events, even hurricanes, you know what to expect. The weather forecast will give you a few hours' warning and some idea of what is coming. This information is thanks partly to hard-working satellites that keep a constant eye on the weather.

However, predicting tornadoes precisely is a different story. Notice that the location with the highest number of thunderstorms does not match the location with the highest number of tornadoes. Many important crops are grown here.

The land is very flat. The area experiences very unstable atmospheric conditions that can lead to the development of supercell thunderstorms. This region of the U.