Presentation on theme: "Thunderstorms. What Are Thunderstorms? Thunderstorms are the most common kind of severe storm. They form in clouds called thunderheads, or cumulonimbus."— Presentation transcript:
What Are Thunderstorms? Thunderstorms are the most common kind of severe storm. They form in clouds called thunderheads, or cumulonimbus clouds. The storms cause huge electric sparks called lightning. The lightning heats up the air and causes the noise thunder. Thunderstorms usually have heavy rains and strong winds.
A thunderstorm starts when intense heating causes air to rise very quickly. A cloud forms where there is an upward rush of heated air, an updraft. As more warm, moist air is carried upward, the cloud grows larger. Strong updrafts keep water droplets and ice crystals in the cloud, so they grow in size, too. When the updrafts can’t support them anymore, they fall as heavy rain or hail.
Once the rain falls, it causes downdrafts in the cloud. When the air going up rubs against air going down, static electricity builds up. When enough builds up, there’s a huge spark—lightning. Lightning may jump within a cloud, between two clouds, or between a cloud and the ground.
How and Where Do Tornadoes Happen? The most violent thunderstorms often spin off even more dangerous storms, called tornadoes. A tornado is a violent whirling wind that moves across the ground in a narrow path. A tornado is a sort of runaway convection cell.
When the updraft in a convection cell is really strong, the air rushes in from all sides at high speeds. The air curves into a spin. This lowers the pressure even more. Air rushes in even faster, and the pressure gets even lower, and so on. Like a spinning skater who pulls her arms in close to her sides, the spinning tornado gets faster and faster.
As the tornado gets stronger, a funnel forms that eventually touches the ground. In the center of a tornado, winds can reach speeds of 500 km per hour (about 300 mi per hour) or more.
Hurricanes Hurricanes are very large, swirling storms with very low pressure at their center. They form over tropical oceans near the equator. Hurricane winds whip up large waves in the ocean. These waves move outward from the storm and pound against a shore for days before the storm arrives. However, it is the storm surge that causes the most destruction. Storm surge or storm plunge is a great rise of the sea along a shore. Its main cause is low air pressure.
How Can Radar Track Storms? Storms are hard to predict because they form so quickly. Scientists use the best methods possible to try to identify conditions long before a storm occurs. They look for clues, like the movement of fronts and the formation of very low pressure areas.
Special methods are used to find storms as they form. One such method is Doppler radar. The word radar stands for radio detection and ranging. Radar works by sending out radio waves and recording their echo. Doppler radar is a very good tool for scientists to track storms. The radio waves reflect off storm clouds and are picked back up again at the radar stations.
Scientists use Doppler radar to find and track thunderstorms, tornadoes, and hurricanes. Doppler radar helps forecasters predict which way the storms will travel.
NEXRAD “NEXt generation of weather RADar”– is a newer form of Doppler radar that is replacing older radar systems. NEXRAD can spot small particles such as blowing dust, very light snow, and even drizzle. NEXRAD is more accurate than conventional radar at predicting floods and flash floods. It can show the exact locations of different fronts. It also shows changes in wind speed and direction. This helps scientists make more accurate weather predictions.