Local Weather

Forecasting the Future: Unraveling the Mysteries of Weather Prediction

Weather prediction has come a long way since the early days of hand-drawn maps and sparse observations. Today, vastly improved observations of the air and oceans, which feed into modern computer simulations of how the atmosphere will behave, have revolutionized the field. However, there is a limit to how far into the future humanity can predict the day-to-day weather.

The limit on this type of weather prediction is somewhere between two and three weeks, said Falko Judt, a research meteorologist at the National Center for Atmospheric Research. This limit is inherent to the atmosphere and cannot be pushed beyond, even with ever faster, better, smarter computers.

The reason for this limit is chaos. Chaos is a powerful property of any system that evolves over time, and it emerges in a prediction when a small unknown or error amplifies. In the atmosphere, chaos thrives because it can’t ever be fully known, to perfection. On the smallest level, it’s impossible to know exactly where an atom is and how fast it’s traveling, a powerful physical law called the “uncertainty principle.” What’s more, even the slightest, little, undetectable whirl or perturbation in the air can dramatically alter the atmospheric future.

This is commonly called “the butterfly effect,” in reference to a butterfly flapping its delicate wings and initiating a cascade of atmospheric events. “People think it’s a metaphor,” said Kerry Emanuel, an atmospheric scientist at MIT. “It’s not. It’s real.”

Scientists’ current ability to better predict day-to-day weather events can certainly improve. It’s a fascinating science. But chaos always reigns by about two weeks. To demonstrate this curious limit, Judt employed thousands of processors at the Cheyenne supercomputer in Wyoming to create state-of-the-art simulations of Earth’s complex, evolving atmosphere. He ran two 20-day simulations: One of real observations taken from a past October day, and the other an artificial creation of that same day modified with a “teeny, tiny” alteration in the weather. Small-scale events, like thunderstorms, materialized in different places within hours. After six days, big weather patterns some 100 miles to 1,000 miles across appeared in different places. By a little over two weeks, the two atmospheres were nothing alike.

Chaos, then, is a defining, unalterable part of our existence. “The discovery of chaos is considered the third greatest discovery of the 20th century,” said Emanuel, behind Einstein’s General Theory of Relativity and Quantum Theory.

The D-Day weather forecast lacked a potent weapon: computers. Soon after the war ended, in 1950, meteorologists made the first weather prediction on a colossal computer. The machine took up a 1,500-square-foot room. Today, weather forecasts are created with far more advanced computer simulations of the weather. These simulations seek to quell chaos.

“I like to talk about taming the butterfly effect,” said Roberto Buizza, a physicist and a former lead scientist for the European Centre for Medium-Range Weather Forecasts. Every forecast must tame chaos because our information about the atmosphere is inherently incomplete. “We have fully embraced the concept of our Earth systems being fundamentally chaotic,” said Peter Bauer, the deputy director of the research department in the European Centre for Medium-Range Weather Forecasts. “We will never have the conditions perfectly observed or simulated.”

In conclusion, while weather prediction has come a long way, there is still a limit to how far into the future we can predict the day-to-day weather. This limit is inherent to the atmosphere and cannot be pushed beyond due to chaos. However, scientists will continue to improve their ability to predict weather events and better understand the chaotic nature of the atmosphere.

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