• 4 months ago
L’Allée des Tornades, traditionnellement située dans le centre des États-Unis, se déplace vers l'est. Des États comme le Kansas et l'Oklahoma étaient auparavant les principaux points chauds, mais maintenant, des régions comme le Mississippi, l'Alabama et le Tennessee connaissent davantage de tornades. Le Sud-Est subit des tempêtes plus graves tandis que les plaines centrales en voient un peu moins. De plus, les tornades cette année sont susceptibles de survenir par groupes - attention ! Animation créée par Sympa.
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Transcript
00:00If you think you're safe from violent tornadoes because you don't live in Tornado Alley, you could be wrong, because this area moves east.
00:09It seems that we will more and more often have access to several powerful tornadoes in one day.
00:15And as it moves to more populated areas, it could make more victims and destroy more houses.
00:22There is not enough time to build infrastructures to preserve everyone from this imminent danger.
00:28So the minimum you can do to protect yourself is to learn as much as possible about it.
00:34Every year, about 1,200 tornadoes hit the United States.
00:38This frequency is due to a unique geography that creates ideal conditions, especially in spring and summer.
00:45The winds of the Pacific bring humidity on the rocks, then become dry and cool as they head east.
00:51They then meet, on a flat ground, hot and humid air currents from the Gulf of Mexico.
00:57This is how the instability of the air and the scratches of the wind are born, perfect conditions for the formation of tornadoes.
01:03Historically, tornadoes were born more frequently in Tornado Alley.
01:07This term was used for the first time in the 1950s by two meteorologists for their research project on the extreme weather conditions of Texas and Oklahoma.
01:17Northeastern Texas and southern Oklahoma are precisely the regions that are mentioned when we talk about Tornado Alley.
01:24But over the last ten years, this area has moved east about 800 kilometers.
01:29Today, Missouri, Arkansas, west Tennessee, Kentucky, north Mississippi and Alabama are seeing more tornadoes.
01:39The early 2023 storms clearly show that this trend is real.
01:44A violent tornado hit Rolling Fork, in Mississippi, and another series of storms caused huge damage in this new Tornado Alley.
01:53The data from the last two years show that the large series of tornadoes,
01:57featuring several whirlwinds from the same meteorological system,
02:01were also moving east, gaining in frequency and intensity.
02:07Tornado Alley moves east, mainly because of supercells.
02:11These powerful storms, with rotating ascending currents, generate new tornadoes.
02:17Supercells are formed when hot and humid air near the ground interacts with fresh and dry air at altitude.
02:24We live in the heart of a real natural experience,
02:28and observe the changes in the basic components of large storms,
02:31without yet knowing how significant these changes are.
02:35Experts predict that supercell storms will become more frequent at the end of winter and early spring,
02:42and less common at the end of summer and fall.
02:45In recent years, the air has become increasingly hot and humid,
02:49and the interactions between air masses are increasingly frequent.
02:53Experts explain that the atmosphere is becoming more unstable,
02:57as the Gulf of Mexico sends more water vapor to the southeast of the United States, thus feeding the storms.
03:03Research also shows that the so-called dry line,
03:07which separates the drier east of the United States from the arid west, also moves east.
03:13Traditionally located along the 100th meridian,
03:16this line has moved about 225 km east since the end of the 19th century.
03:22This movement can affect the places where storms form,
03:25because the dry line acts as a boundary for convection,
03:28where hot air rises and cold air descends, which gives birth to storms.
03:33The milder winters observed recently also increase the chances that these unstable air masses interact
03:39and form supercells earlier in the year.
03:41It is difficult to predict how the situation will evolve and what danger it represents,
03:46because we do not have a lot of data on the impact of meteorological conditions
03:51on phenomena as ephemeral as tornadoes.
03:54The U.S. Meteorological Service did not begin to record tornadoes until 1950,
04:00and it did not record many tornadoes in the receded areas.
04:04The data shows that the number of days affected by tornadoes each year has decreased,
04:08but that the tornado activity is then more intense.
04:11Records also show that in some years, tornadoes kill up to 20 people in the United States,
04:17while in other years, they can cost more than 100 lives.
04:21Today, there are more people living on the path of tornadoes,
04:25because the population of the United States has more than doubled since 1950,
04:29and the southeast, where the activity of tornadoes could increase, now has many more inhabitants.
04:35Texas and Oklahoma are well protected from tornadoes, but the regions of the southeast are not.
04:41In addition, there are many mobile homes, particularly vulnerable to storms, in the southeast.
04:47Tornadoes in this region often strike at night and are 2.5 times more likely to cause human losses.
04:54We could observe more events similar to the Super Tuesday 2008 tornado epidemic.
05:00This one hit the south of the United States and the Ohio Valley,
05:04and in just 15 hours, 87 tornadoes tore through the region, causing enormous damage.
05:1057 people lost their lives in 4 states and 18 counties, and many others were injured.
05:16Tornadoes were fed by powerful low-pressure systems that brought record heat.
05:22Supercells and rotating winds then produced these violent tornadoes.
05:27Early in the day of February 5, a grain line formed from eastern Texas to Missouri and moved east.
05:35One of the most intense tornadoes traveled 200 kilometers in just two hours.
05:40On the early morning of February 6, the threat moved east of the United States,
05:45its winds causing ravages, while the cold was heading towards the Atlantic.
05:49Snow and ice were spreading from Iowa to Quebec.
05:53The storm damaged many houses, tore some of their foundations, and took away the mobile homes.
05:59Several vehicles and semi-trailers were thrown off the highway and thrown against the trees.
06:04Winds of more than 80 kilometers per hour blew from Arkansas to Indiana.
06:10We observed hail of the size of a tennis ball,
06:13trees overturned, and power cuts everywhere.
06:17Some areas were flooded due to heavy rains and snow melting.
06:22All this led to more than 1,000 cancellations at the Chicago airport
06:26and disruptions at the Toronto airport.
06:29Scientific data can help the new hit regions of the United States
06:33prepare for the arrival of new tornadoes.
06:36Authorities will have to improve collective shelters and alert systems,
06:40as well as educate residents on safety measures in the event of a tornado.
06:45You can also prepare by following three basic rules.
06:48Go home, lower yourself, and cover yourself.
06:51When you hear an imminent tornado alert,
06:54take refuge in the room that is closest to your house,
06:57and stay away from doors and windows.
06:59If you have a cave or an anti-tornado shelter, hide there.
07:03Otherwise, just make sure you are on the floor as low as possible.
07:07Use everything you have on hand to protect yourself from debris.
07:10Clothes, pillows, blankets, a mattress or a sturdy table.
07:14Anything will do.
07:16It is often said that the bathroom is the safest place to hide.
07:20This seems logical because they are generally located in the center of houses.
07:24In March 2023, a man and his girlfriend in Rolling Fork, in Mississippi,
07:29survived a tornado in their bathtub.
07:32They were thrown into the air but landed safely in the middle of the debris of their mobile home.
07:37However, there is nothing particularly safe to hide in a bathtub with a mattress.
07:42Italian-style cupboards and showers, located deep inside the building,
07:46can also provide good protection.
07:49Do not use elevators.
07:51You could get stuck in case of a power outage.
07:54Stay in your shelter until you are sure that the threat has passed.
07:58If possible, listen to weather service news on local radio or television.
08:04Several tornadoes can hit the same region,
08:07so they may not be sure to leave even after a tornado has passed.
08:12When you leave your shelter, be very careful.
08:15There could be floods, landslides, collapsed buildings and blocked roads.
08:20Stay away from downed power lines and puddles of water or cables,
08:25and do not use a match or lighter in case of a gas leak.
08:29Avoid damaged buildings because they could collapse at any moment.
08:33Being in a car during a tornado is much safer than being outside or in a parking lot.
08:39Many people are regularly injured trying to escape storms,
08:43and tornadoes can cause tennis ball-sized hail that can easily break a windshield.
08:49If you are outside when a tornado strikes, try to find a shelter.
08:55If this is not possible, stay as low as possible.
08:59Even a ditch or a ditch can be safer than your vehicle.

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