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Groundhog Day: How accurate is Punxsutawney Phil?

Did Phil see his shadow this Groundhog Day? Yup. Does that mean anything? Not really.

By / February 2, 2010

Punxsutawney Phil is lovable, sure. But is the Groundhog Day hero an accurate weather forecaster?

Jason Cohn/REUTERS

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Like most TV weathermen, Punxsutawney Phil is more about style than science. Each Groundhog Day, people gather at Gobbler's Knob in Pennsylvania to await a winter weather prediction from America's favorite furry forecaster.

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Today, the marmot meteorologist saw his shadow, foretelling six more weeks of winter. But just how accurate is Groundhog Day?

Flipping through the history books, it seems Punxsutawney Phil has spotted his shadow 99 out of 114 times. That would mean poor Pennsylvania rarely gets an early spring. However, according to the Stormfax Almanac, the groundhog is only right 39 percent of the time – a failing grade in school terms. (PETA wants to replace him with a robot groundhog, maybe that would help his chances.)

But can you blame him? Most professional weathermen, armed with high-tech satellite imagery and advanced computer models, wouldn't dare guess six weeks into the future. Their accuracy drops quickly even three days out.

In 2008, "Freakonomics" co-author Stephen J. Dubner linked to a report on the precision of TV forecasters: "For next day predicting (one day out), all stations met their 'within three degrees' goal. For two days out, all but one was within three degrees. But for three days out and beyond, none of the forecasters met their three-degree benchmark, and in fact get linearly worse each day."

Then again, maybe Punxsutawney Phil is more like the Farmers' Almanac. It predicts temperature trends for an entire year. How accurate is it? Pretty good – if you compare the Almanac to its TV counterparts. (But that's not saying much.) A survey by the Weather Underground shows varying reports on the annual guide – ranging from 50 to 80 percent accuracy. Better than a groundhog, but not enough to bet the farm on, say most experts.

"The results of my forecast verifications and those done by several others indicate that there is little reason to believe the Old Farmer's Almanac claim of 80% accuracy," writes a Weather Underground blogger. "Unless the Almanac posts some scientific evidence to the contrary, I won't believe their forecasts are any better than flipping a coin."

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Which do you trust more: TV meteorologists, the Farmers' Almanac, or Punxsutawney Phil? Let us know in the comments. And follow us on Twitter for more sci-tech news and explainers.

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