In the 1960s, weather scientists found that the chaotic nature of Earth’s atmosphere would put a limit on how far into the future their forecasts might peer. Two weeks seemed to be the limit. Still, by the early 2000s, the great difficulty of the undertaking kept reliable forecasts restricted to about a week.

Now, a new artificial intelligence tool from DeepMind, a Google company in London that develops AI applications, has smashed through the old barriers and achieved what its makers call unmatched skill and speed in devising 15-day weather forecasts. They report in the journal Nature on Wednesday that their new model can, among other things, outperform the world’s best forecasts meant to track deadly storms and save lives.

"It’s a big deal,” said Kerry Emanuel, a professor emeritus of atmospheric science at the Massachusetts Institute of Technology who was not involved in the DeepMind research. "It’s an important step forward.”