Such a big question and I'll try and explain it briefly and if anyone wants to elaborate and improve it please do. The U.S experiences all climate extremes because of its sheer size and topography. Tornadoes are 'common' (they aren't that common, many sources approximate 1,000 reports a year, this year looks like it will surpass that.) because of a number factors and I'll pin point the main one which includes supercell formation. A classic answer to why a severe weather event occurs especially in terms of the U.S, is the hot air cold air collision which is partially true but nowhere near an actual answer. You need instability and on a late spring day in states such as Texas, Oklahoma, Kansas et al many ingredients are present for severe weather which can create a tornado in exceptional circumstances. So basically convection, high humidity and wind-shear can create a steady state storm. (that really is basic, look up supercell on wiki there is more to it) A tornado comes about from the creation of a mesocyclone which is a small scale rotation within the cloud which is typically two to six miles wide. This is created primarily by wind shear (in this case often a veering wind, so a clock-wise change of wind direction with height) again look up these terms to find out more. The mesocyclone always seems to position itself in a similar area within the supercell and a lowering called a wall cloud can form and it is at this point where tornadoes become a possibility. Wall clouds form because of precipitation cooling which causes air to descend within the system and it creates the lowering. Again other things play a part as well in that!
Heres the annoying part which almost makes my write up pointless but I, like many other people love severe weather can could probably talk about it for days! Why a tornado forms from this lowering is not known for certain! A generally accepted theory is that an exceptionally large updraft of air caused by the interaction of the storm system and it's environment creates a funnel and once in contact with the ground it creates havoc and generally speaking the more energy the storm has, the stronger the winds the tornado will have. Look at Moore, Oklahoma tornado may 3rd 1999. That had a tremendous amount of energy and the damage photos from that day say it all. The size of the storm compared to the size of the tornado has not been proven though so don't take it as fact. The size of a tornado in its literal sense does not necessarily create the most damage either.
so tornadoes are most likely to form in unstable conditions with wind-shear present (the jet stream can help greatly here too.) Theres a lot more points to cover but for further reading look up
. CAPE
. Positive vorticity advection
. RFD and FFD (i think supercell on wiki covers these points)
. Hook echo
and to get an idea of instability look up lapse rates.
The US has many tornadoes due to a combination of geographical factors, such as the collision of warm, moist air from the Gulf of Mexico with cool, dry air from Canada, and the presence of the Rocky Mountains to the west. These conditions create the ideal environment for the formation of tornadoes, particularly in the central region known as Tornado Alley.
There were 1424 confirmed tornadoes in the U.S. in 1998, making it an active year.
On average, there are about 1,000 tornadoes reported each year worldwide. However, the actual number could be higher as not all tornadoes are observed and reported. The United States experiences the most tornadoes of any country, with an average of about 1,250 tornadoes annually.
Tornadoes actually occur more frequently in the US than in England due to geographic and climatic factors. The US has a larger land area and a more diverse climate, leading to a higher frequency of severe weather events that can produce tornadoes. England, on the other hand, has a milder climate and is surrounded by ocean which tends to stabilize the atmosphere, making tornadoes less common.
well they have about 3 tornadoes each year
The idea is that studying tornadoes, which sometimes means getting close to them, allows us to better understand them. A better understanding of tornadoes may help us predict them, which would mean better warnings for people who might be in the path of a tornado.
There were 1692 tornadoes in the U.S. in 2008.
In 2011 there were 1,626 tornadoes and 552 deaths.
Generally, the highest number of tornadoes in the U.S. occur on the Great Plains, so much so that the region is sometimes called Tornado Alley. The region experiences as many as 800 tornadoes per year.
There were 1,103 tornadoes in the U.S. in 2006.
There were 1297 recorded tornadoes in the U.S. in 1992.
There were 1173 confirmed tornadoes in the U.S. in 1993.
There were 1082 recorded tornadoes in the U.S. in 1994.
There were 1235 tornadoes recorded in the U.S. in 1995
There were 1173 recorded tornadoes in the U.S. in 1996.
There were 1,692 confirmed tornadoes in the U.S. in 2011.
There were 940 tornadoes recorded in the U.S. in 2012.
There were 1159 confirmed tornadoes in the U.S. in 2009.