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An example of a hook echo.
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Tornado Forecasts

The short duration and complicated nature of tornadoes make them nearly impossible forecast. Meteorologists don't really know the specifics of how they form, but they do know what atmospheric conditions were present during past tornadoes. They use this knowledge to try and identify tornado threats before they happen. The earlier they realize that a tornado is going to strike, the earlier they can notify residents of the areas which will be hit. The more warning people have, the fewer people will be killed.

To know the current atmosphere conditions, meteorologists send up weather balloons every twelve hours to take soundings of the upper atmosphere. The equipment on the balloons measure conditions such as the atmospheric stability, temperature, and relative humidity. Two conditions tornadoes need to form are high instability and a high dew point. When these conditions exist, they issue a tornado watch.

A new type of weather radar can greatly improve the time between tornado detection and tornado touchdown. Conventional radar could only be used to detect a tornado after it had formed, usually by seeing a shape such as a hook echo on the radar return. The echo doesn't appear with every tornado, so forecastor can't rely on just that information. They also need observations from tornado spotters in order to issure a tornado warning.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA