Friday, August 14, 2009

10 things weather forecasters won't say

1. “Long-term forecast? Your guess is as good as ours.”

WEATHER FORECASTERS have gotten pretty good at nailing the outlook two to three days ahead. The problem is, “everyone wants to know what the weather is going to do next weekend,” says Paul Karpowicz, president of the Meredith Broadcasting Group, and forecasting the weather a week or more down the road isn’t so easy.

Eric Floehr, founder of ForecastAdvisor, which tracks the accuracy of predictions, looked at high-temperature forecasts from the National Weather Service, AccuWeather and other organizations for 2008 and compared their
numbers with actual temperatures. When predicting highs for the following day, they were off by about three degrees; when forecasting nine days out, they missed by nearly seven degrees. Doug Young, performance branch chief at the National Weather Service, says his organization’s precipitation forecast for seven days out is only 55 percent accurate. “You’re almost flipping a coin at that point,” he says. Ray Ban, consultant for The Weather Channel, says the best forecasters can do is try to convey the uncertainty of long-range predictions.

2. “We’re pretty accurate—as long as the sun is shining.”

ONE OF THE MOST important things forecasters can do is tell you when bad weather is on the way. Unfortunately, they’re not very good at predicting rain. That’s especially true in summer, when most rainfall comes from thunderstorms, which are small, unpredictable and hard to track. It’s often difficult to tell where they’re headed or whether they’ll produce any rain. Most models for forecasting weather divide the country into a grid of squares that cover about 55 square miles each, though some have smaller squares. Whatever the square’s size, rain, snow, sun and temperature are forecast as a whole for each one. Since most thunderstorms are smaller than the squares, it’s tough to predict exactly where it will rain. “Forecasters are terrible at telling you if rain is going to fall where you live tonight,” says William Gallus, a meteorology professor at Iowa State University.

(The author is a bit harsh in spots, but yes, we need to take our lumps, like any other profession. Then again, you have to be borderline insane to even contemplate wanting to predict the weather. The rest of the article from is here.)

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