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The Groundhog Is Only a Little Worse Than an Almanac at Predicting Weather

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Predicting the weather is not easy. Right now, we know a few things: Generally, things are getting warmer. If it’s an El Niño year, weather patterns will differ. But ultimately, the weather is a super-complex physics problem with tons of moving pieces that make totally accurate forecasting difficult and reliant on models and probabilities.

Groundhog Day is an old superstition, reliant on old superstition. But it’s not much worse at predicting six weeks of cold weather than, say, an almanac.


Punxsutawney Phil saw his shadow today, and superstition says that this means there will be six more weeks of winter in Pennsylvania. But first, what’s “winter” exactly? North of the equator, it’s a human-defined timeframe based on the fact that the Earth rotates around a tilted axis. It spans from the hibernal solstice, when the Northern hemisphere is tilted away from the Sun, to the vernal equinox, when sunlight strikes both hemispheres equally. Based on that measurement, there will always be around six more weeks of winter, regardless of what the magic groundhog saw. That’s just how long we’ve got until the vernal equinox. Meteorologists tend to rely on meteorological winter, which ends whenever February does.

If you’re a farmer, the “winter” label doesn’t matter as much as the actual weather does.


The groundhog can’t predict the weather, obviously. But there’s a long history of using animal behavior to try to make forecasts. It’s not totally off-base, if you think about the fact that the Pennsylvania Dutch didn’t have computer modeling a hundred years ago. So they relied on superstition to do a check-in halfway through the winter to see how much longer the cold would last. Some animals really can sense impending weather changes, after all. More importantly, they used to eat the groundhog, a tradition that I wish still existed.

So really what I’m trying to say is that, well, Groundhog Day is completely unscientific, but isn’t as crazy as it seems. I will say that the groundhog has gotten things right about 39 percent of the time. It’s hard to tell whether there really is some reason Phil is bad at predicting the weather, or if this whole experiment is just a coin toss in the middle of an unlikely unlucky streak.

Almanacs, on the other hand, use some “secret formula” that they brag about. This formula combines science and tradition, according to CNN. One often-cited statistic from a 1981 paper states that the Farmer’s Almanac is only right about 50 percent of the time—another coin toss.

Predicting the weather is hard in general—after all, it’s an incredibly complex non-equilibrium thermodynamics problem, perhaps one of the most difficult kinds of physics problems there is. Meteorologists have gotten good at forecasting a few days out, but at a month, their models, too, are probabilistic. NOAA’s prediction is that there’s a 40 percent to 50 percent chance that things will be colder than usual in the Northeast this February, for example.


As a reminder, studying the climate is a very different matter, focused instead on the biggest factors affecting longer-term trends. I am not talking about the climate.

So, to summarize: It’s hard to predict the weather. If you’re a farmer, either you can trust expertise, which will not give you a specific answer but is likely to get you a rough sense of what’s going on, or you can trust superstition, which will give you a specific answer that has only a 40% chance of being correct. I pick the weather forecast, but I won’t be mad if you pick the hog.


Also, I think it’s time we eat Phil.