Lesson 20， Scourge of the Plains： Tornadoes
平原之祸——－龙卷风
Ellen Mae stepped out of her two-story home in certral Illinois. "Fine morning，" sae said to herself after checking the weather， and then went back inside. The radio had mentioned a severe storm advisory， but the sky was clear， and it was rather calm. Still， she decided to be safe and kept her radio on.
About noon she felt a strange kind of pressure. Looking out her window， she noticed the sky had become overcast. Low， rounded， oddly colored clouds were forming. It was still and oppressive. "Maybe I'd better listen to the weather report again，" she murmured to herself.
Again the radio forecast severe weather， warning citizens to listen for the siren and seek shelter should a twister， scourge of the plains， come down from the heavens like a "Devil's tail." "I doubt it'll happen over Crossville，" she comforted herself. "It always happens in other towns."
By two o'clock it started to rain， and the wind picked up， too. The apple tree in front of Ellen Mae's house started to pitch back and froth violently. Her dogs started to bark and howl， and that was when she heard that awful sound.
At first she thought it was a locomotive， but she quickly remembered that there was no railroad within 20 miles of her home. She looked into the sky and then noticed it， a dark， swirling mass of back cloud sucking up everything it touched and hurling objects at horrific speeds straight up or straight to the side. Ellen Mae ran as fast as she could down into her storm cellar， a special room which had been prepared by her father when he was still alive. This room was located in the southwestern corner of the basement and had a door with a strong bolt. Ellen Mae ran in， locked the door behind her， and waited.
She didn't have long to wait. With shrieking and swooshing sounds right out of hell， the funnel cloud passed directly over her house. An enormous vacuum cleaner， the twister blew the house apart， scattering five generations of Ellen Mae's family belongings over half the rural country she lived in. Within minutes， the winds had stopped， and an eerie silence replaced the cacophony of moments earlier. Feeling it was now safe to venture out， Ellen Mae unbolted the door， peered out， and started to cry. She could look straight up into the sky. Even though she had lost her house and everything in it， she felt lucky. She knew that every year， hundreds of people could perish in tornadoes.
Just what are these "devil storms"？ They go by many names across the great Plains of the United States and Canada， not to mention many other countries around the world， but tornadoes are perennial plagues in central North America. The conditions there——flat land and proximity to cold air masses （from the Rocky Mountains to the west） and warm and humid air masses （from the Gulf of Mexico to the south） provide the optimum breeding ground for tornadoes. According to the US National Weather Service， tornadoes form from thunderclouds and can reach swirling speeds in excess of 600 kilometers per hour. They last from minutes to an hour or more and can blast their way across as much as 150 kilomiters of terrain at about 50 kilometers per hour. They vary in width from a few metres to 1500 meters （average 200 meters）。 And they strike fear into the hearts of everyone.
The safest place to be when a tornado is in one's area is a basement， preferably the southwest corner （where the tornado normally comes from）。 If driving， track due north or south， as tornadoes usually move from west to eat. Weather prediction and tracking these days is far superior to earlier years， but tornadoes can appear without any warning at all， as a large one did right in the heart of Salt Lake City in 1999， leaving a trail of shocked， wounded， and dead as well as pulverized property.
Though relatively few people have ever seen a tornado， those who have wish they hadn't. The "Finger of God" is nature's atmospheric fury at its worst.
