Word: tornados
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Storm chasing as an organized enterprise began in 1972, when the Tornado Intercept Project was launched to provide what radar meteorologists refer to as "ground truth." At the time, the NSSL was developing a radar capable of detecting areas of strong rotation inside big tornado-producing storms. The chasers provided visual proof that particular radar signatures did indeed precede the formation of tornadoes. The new radar, Doppler radar, made use of the fact that radio waves shift frequency depending on whether the objects they bounce off are advancing or receding. In this case, the objects that create the Doppler shift...
...collaboration between radar developers and storm chasers was immensely productive. It led to the NEXRAD (or Next Generation Radar) system, which the National Weather Service is currently installing nationwide. Already NEXRAD has helped extend the lead time for tornado warnings from three to eight minutes, on average. Sometimes the warning comes even earlier. Last month weather forecasters in Little Rock, Arkansas, called a tornado warning for communities in the Ozark Mountains a full 35 minutes before the twister showed up, giving people who lived in trailer homes time to scurry to friends' basements for safety...
Good as it is, however, the NEXRAD system has not changed the rate of false alarms: 50% to 70% of the warnings forecasters issue are not followed by tornadoes. Why does one threatening-looking storm produce a tornado while others seemingly just like it do not? This question has dogged tornado experts for years, and the VORTEX project was launched to answer it. First in 1994 and again in 1995, VORTEX brought dozens of meteorologists to Oklahoma, Texas and Kansas during May and June--peak tornado season in that part of the country. Every few days for nearly 10 weeks...
...VORTEX scientists managed to encircle 10 tornadoes in their virtual lasso, and the data they recorded--wind speed, temperature, pressure, humidity--have turned out to be extraordinarily rich. "We got more good data out of VORTEX," exclaims Peter Hildebrand of the National Center for Atmospheric Research, in Boulder, Colorado, "than we had collected in the past 30 years." Among other things, the chase teams managed to position a Turtle so it actually caught the sharp pressure drop as a VORTEX passed overhead; tucked into the center of the tornado's swirling interior, a cylinder of down-flowing air that...
...collision between warm and cold air masses sets up conditions that favor the growth of big thunderstorms. A tornado, however, requires something else as well: the presence of what meteorologists call wind shear. This occurs when winds in the so-called boundary layer--the part of the atmosphere closest to earth--blow more gently than winds at higher elevations. These two wind streams push on the layer of air that lies between them as though it were an invisible rolling pin. Then, as the warm updraft that powers a supercell shoots toward the stratosphere, it tilts the rolling...