This is America. Гришенкова Е.Г. - 109 стр.

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109
Tornado seasons are the result of wind and weather patterns. During spring,
warm air moves north and mixes with cold air remaining from winter. In autumn, the
opposite happens. Cold weather moves south and combines with the last of the warm
air from summer.
Tornadoes can strike with little or no warning. Most injuries happen when
flying objects hit people. Experts say the best place to be is in an underground shelter,
or a small, windowless room in the lowest part of a building.
People driving during a tornado are told to find low ground and lay flat,
facedown, with their hands covering their head. People in the path of a tornado often
just have minutes to make life-or-death decisions.
The deadliest American tornado on record was the Tri-State Tornado of March
18, 1925. It tore across Missouri, Illinois and Indiana. About seven hundred people
were killed.
A "tornado outbreak" is often defined as six or more tornadoes produced by the
same weather system within a day. But the outbreak of April 3 and 4, 1974, set a
national record. It is remembered as the "Super Outbreak." One hundred forty-eight
tornadoes struck during a twenty-four-hour period. More than three hundred people
were killed and nearly six thousand others injured.
No two tornadoes look exactly the same. And no two tornadoes act the same way.
Even a weak tornado requires the right combination of wind, temperature,
pressure and humidity. Weather experts can identify these conditions. And, when
they observe them, they can advise people that tornadoes might develop. But they are
not able to tell exactly where or when a tornado will hit. Tornado warnings still
depend in large part on human observations.
Usually a community will receive a warning at least a few minutes before a
tornado strikes. But each year there are some surprises where tornadoes develop
when they are least expected.
The tornado reporting system involves watches and warnings. A tornado watch
means tornadoes are possible in the area. A tornado warning means that a tornado has
been seen. People are told to take shelter immediately.
Yet tornadoes can be difficult to see. Sometimes only the objects they are
carrying through the air can be seen. Some night-time tornadoes have been observed
because of lightning strikes nearby. But tornadoes at night are usually impossible to see.
Tornadoes that form over water are called waterspouts. But tornadoes cover a
much smaller area than hurricanes, which form over oceans.
Tornadoes can be measured using wind speed information from Doppler radar
systems. Tornadoes usually travel in a northeasterly direction with a speed of thirty-

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