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Better Weather Radar

Radar display of the Hurricane Fred center.

NOAA

Tornadoes are a scary threat -- not just because they kill hundreds of people in the U.S. each year, but because they long have been notoriously difficult to predict and track. But National Weather Service forecasters are now using a technological advance that they hope will enable them to better predict where tornadoes are headed.

The service's existing NEXTRAD radar system has long relied upon 150 massive radar antennas spread across the country, which sit on dedicated towers several stories high, and track storms that are more than 100 miles (162 kilometers) away. But the old system has limitations. Because the pulses of electromagnetic radiation that the antennas send out travel in straight lines, the Earth tends to block their view of anything that's far away and also close to the ground. That works out to a blind spot that covers about 75 percent of the atmosphere below 1 kilometer (0.62 of a mile) in altitude, which is where a lot of weather occurs.

CASA (Collaborative Adapting Sensing of the Atmosphere) radar, a system developed by a consortium of universities, tries to fill in that coverage area with a vast number of smaller antennas attached to buildings and cell towers. In a 2011 test, researchers found that CASA helped them to see that a tornado in the Chickasha, Okla. area was veering north, and to direct first responders to the stricken area within minutes [source: Hamilton].

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