If you would've asked the NOAA's Climate Prediction Center last fall how the upcoming winter was looking, they'd have told you not to invest in a down coat. The official U.S. forecast predicted above-average temperatures for the lower 48 states from November through January.
From the other side of the blizzardy, polar vortexy winter it's turned out to be, the suggestion seems downright offensive..
“Not one of our better forecasts,” Mike Halpert, the Climate Prediction Center’s acting director, told Businessweek, explaining that, on a scale from -50 to 100 (with 100 representing perfection), the agency rated its own performance as a -22. Here's why, according to Halpert, “sometimes trying to figure out why something happened is as hard as making the forecast of what will happen":
The techniques that go into three-month climate forecasts are completely different from the ones used for daily weather forecasting. The daily stuff, says Halpert, is based on “initial conditions”—i.e., measuring as precisely as possible the current state of the atmosphere and predicting how it will evolve over the coming few days. Regardless of what Siri might say, weather forecasts have very little accuracy past a week.
Months-ahead climate forecasts are what Halpert calls “boundary-value problems.” Instead of taking a snapshot of the quickly changing atmosphere, climate forecasters focus on things that change more slowly, like temperatures of the land and oceans. The concept is that these enduring conditions will “force” the daily weather in a certain direction. Climate forecasters can’t say when a storm might hit, but they try to say whether a given three-month period will be wetter, drier, hotter, or colder than average. (Here’s a good description of the difference between weather and climate forecasting from University of Toronto computer scientist Steve Easterbrook.)
Climatologists, according to Businessweek, are chalking this one up to a "learning experience."
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