why do tornadoes occur in the us

No terrain is safe from tornadoes. If a tornado warning is issued, move to a safe place or shelter, such as a basement or under a sturdy piece of furniture. Stay away from windows. If you are in your car when a tornado warning is issued, get out the car immediately and seek shelter. Tornadoes, considered to be nature s most violent storms, are more common in the United States than in any other country in the world, according to thePNational Oceanic and Atmospheric OrganizationP(NOAA), which operates the National Weather Service. While there has been a tornado recorded for every U. S. state, some parts of the country are more prone than others to tornadoes. What Causes a Tornado? Tornadoes should be taken seriously because they can cause much destruction, even uprooting trees and knocking down buildings. Winds can reach more than 300 miles per hour. Thunderstorms usually start most tornadoes, along with a clash of warm, most air with cool, dry air. This clash causes an unstable atmosphere and creates a spinning effect of rotating air that rises vertically. When a funnel cloud like this touches down upon the ground, it s categorized as a tornado. East of the Rocky Mountains is where tornadoes most often occur, specifically in a sub-region known asPTornado Alley. Tornado Alley includes the Midwest states of Iowa, Kansas, Missouri, Oklahoma, and Nebraska, as well as the southern state of Texas. Not included within Tornado Alley but also known for strong tornado activity are the Southeastern states of Mississippi, Georgia, and Florida. The map above shows the average annual reports of tornadoes in the United States, with yellow representing 1 to 3 tornadoes reported per year, orange representing 3 to 5 tornadoes reported per year, and red representing 5 to 10 tornadoes reported per year.

There has been a tornado recorded for every month of the year, but spring and summer are the seasons when tornadoes happen most often. Western States: May to July (except California, where the season runs from January to April)
Check out this map ofP. What s the Difference Between a Tornado Watch and a Tornado Warning? The National Weather Service defines aPtornado watchPas meaning: Tornadoes are possible in your area. Remain alert for approaching storms. The National Weather Service defines aP tornado warningPas meaning: A tornado has been sighted or indicated by weather radar. If a tornado warning is issued for your area and the sky becomes threatening, move to your pre-designated place of safety. There are environmental and auditory cues to alert you to the possibility of a tornado. They are, according to NOAA: Dark, often greenish sky You can also tune in to the television and radio, as the National Weather Service issues announcements in the event of a tornado watch or warning in the form of a news crawl or an Emergency Broadcasting System test. Otherwise, a smartphone app that is capable of issuing push notifications, such as the free one fromP, is ideal. What Are Some of the Deadliest Tornadoes in US History? The Tri-State Tornado killed nearly 700 people and injured more than 2000 more in March of 1925, ripping through Missouri, Illinois,Pand Indiana. The Natchez Tornado traveled along the Mississippi River in both Louisiana and Mississippi in 1840 killing more than 300 people. The St. Louis Tornado happened in 1896 and winds may have reached up to 260 miles per hour. More than 250 people were killed 255 people and about 1000 people were hurt. Oklahoma s devastating tornado, which at least 24 people and injured more than 200 others, is drawing comparisons to past U. S. twisters today, including the that hit the same region in 1999.

And the United States has plenty of examples to draw from. According to the (NOAA), the United States, in averaging more than 1,000 tornadoes each year, is by far the global leader when it comes to number of twisters recorded. Canada finishes a distant second with roughly 100 per year. Here s NOAA s map of the regions of the world that are most likely to experience tornadoes. In addition to the United States and Canada, the organization highlights many European countries and parts of other nations including Argentina, South Africa, Bangladesh, and Japan (click on the image below to expand): So why is the United States so disproportionately prone to tornadoes? According to a explainer on the subject, the distinction is a result of climatology, geography, and topography (the NOAA image at the top of this post shows this week s storm system over Moore, Oklahoma): [T]he United States has an abundance of flat, low-lying geographic regions, and it also has a climate that is conducive to intense thunderstorms, and tornadoes tend to form during thunderstorms. Turning for a moment from topography to geography, the United States has a few places that might be called tornado hotspots. Most prominent among them, of course, is Tornado Alley, a slice of America s mid-section running horizontally from Texas up to North Dakota taking in portions of Oklahoma, New Mexico, Colorado, Kansas and Nebraska. Tornado alley s tornadoes usually happen later in the spring time and sometimes into the fall. The region is considered a prime breeding ground for supercell thunderstorms, which tend to produce the strongest tornadoes. Supercell thunderstorms contain something called a mesocyclone, which has a rotating updraft they re very dangerous but also, when identified as supercells, can provide a good heads-up that the extreme weather they can produce, like tornadoes, is possible.

Florida, too, has lots of tornadoes. That s because the state has many thunderstorms on a daily basis, and it s also a pit stop for many tropical storms or hurricanes (the tropical storms and hurricanes don t tend to produce the kind of killer tornadoes that come about during non-tropical storms). While the United States leads the world when it comes to sheer volume of tornadoes, the ranking changes when you apply other filters. The United Kingdom, for example, has more tornadoes relative to its land area than (a fact one expert to the country s position on the Atlantic seaboard, at the nexus of polar air from the North Pole and tropical air from the Equator). And factors such as high population density, ineffective warning systems, and shoddy infrastructure mean tornadoes can be particularly deadly in countries like Bangladesh, which experienced a tornado that killed in 1989. Writing for, Peter Tyson points out that America s tornado tally may be so high relative to the rest of the world in part because other countries aren t as diligent about recording twisters. And he adds that all nations that experience tornadoes have something in common: They lie 20` to 50` on either side of the equator, in the mid-latitudes. You could probably get a tornado anywhere on the planet, but there are places where they are far less frequent, says John Snow, a tornado expert at the University of Oklahoma. For good meteorological reasons, these tend to be in the tropics and the very high latitudes. The only continent where twisters have yet to strike? Antarctica.

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