Irma Shifting Forecasts: It’s All a Matter of Probability
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Many people trying to use forecasts like those provided by the National Hurricane Center, however, do not fully understand the cone of probability and focus instead on the line that runs down the middle, taking it as an accurate prediction of the storm’s path.
J. Marshall Shepherd, an atmospheric scientist at the University of Georgia, explained the fallacy in a Facebook post. “Anywhere in that cone is a possibility,” Dr. Shepherd wrote, “and it has always been a challenge communicating what the cone ‘means’ versus what people ‘think’ it means.”
He wrote it was “somewhat similar to why we have to issue rain forecasts as ‘percent chance of rain’ rather than telling you exactly that it is going to rain on your house at 5:42 p.m.”
That leaves a gap between what the computer models can do and what people need, said Matt Lanza, a weather forecaster in the energy industry and managing editor of the site Space City Weather.
The fact that the track was within 50 to 75 miles of where the storm is headed is “a good forecast, in model speak,” Mr. Lanza said. “But from a human perspective, it poses enormous communication and risk challenges.”
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