Zhang hoped that the next generation of supercomputer-powered weather models, including those run by the European Centre for Medium-Range Weather Forecasts and the U.S. But until recently, global weather prediction models lacked the high resolution needed to test it by recreating the storm-forming processes driving the atmosphere's chaos. Lorenz's idea has been validated in theory. If real, this 2-week descent into chaos would set a fundamental limit to the atmosphere's predictability. "That was a revolutionary insight," says Richard Rotunno, a meteorologist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, who was not involved in the new study.
A 1969 paper by Massachusetts Institute of Technology mathematician and meteorologist Edward Lorenz introduced this dynamic, later dubbed the "butterfly effect." His research showed that two nearly identical atmospheric models can diverge widely after 2 weeks because of an initial disturbance as minute as a butterfly flapping its wings. A tiny disruption in one layer of turbulence can quickly snowball, infecting the next with its error. It's as close to be the ultimate limit as we can demonstrate," says Fuqing Zhang, a meteorologist at Pennsylvania State University in State College who led the work, accepted for publication in the Journal of the Atmospheric Sciences.įorecasters must contend with the atmosphere's turbulent flows, which nest and build on each other as they create clouds, power storms, and push forward cold fronts. In the regions of the world where most people live, the midlatitudes, "2 weeks is about right. Today, the best forecasts run out to 10 days with real skill, leading meteorologists to wonder just how much further they can push useful forecasts.Ī new study suggests a humbling answer: another 4 or 5 days. Since the 1980s, they've added a new day of predictive power with each new decade. A week later, that unlikely forecast came true-testimony to the remarkable march of such models. Last month, as much of the United States shivered in Arctic cold, weather models predicted a seemingly implausible surge of balmy, springlike warmth.
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