Okay, campers, rise and shine, and don't forget your booties 'cause it's cooooold out there today.

February 2, 2009 9:44 AM

How accurate is Punxsutawney Phil?

If Punxsutawney Phil sees his shadow we are supposed to in for six more weeks of winter. Clearly, this isn't science, but how many times has the little "rat" correctly predicted the winter?

posted by Steve_at_Linnwood to science & nature (9 comments total)

Apparently it's 50% (same for Wiarton Willy and Shubenacadie Sam - two Canadian groundhogs)

The Guardian wrote about this today

link

And here's the answer halfway through the article:
An American newspaper's study suggests the celebrity groundhog may as well flip a coin as glance around for his shadow. In a study published this morning, the Atlanta Journal-Constitution found that Phil's predictions are accurate only 50% of the time, based on whether the temperatures in February or March are above or below the average.
posted by any portmanteau in a storm at 9:49 AM on February 2

His Wikipedia page states that Phil is 39% accurate. Georgia's General Beauregard Lee hasn't been at it as long, but boasts an 94% accuracy.
posted by ijoshua at 9:49 AM on February 2

From the Wikipedia article on Phil: As to his accuracy, according to the Punxsutawney Groundhog Club Inner Circle, he is 100% accurate. However, according to StormFax Weather Almanac, his accuracy is just 39%.
posted by amro at 9:51 AM on February 2

If you define winter by any arbitrary set of climate variables rather than simply the time between the winter solstice and the vernal equinox (or two calendar dates or something else that can be precisely defined), you can choose your definition of winter such that the groundhog is as accurate or inaccurate as you want. For example, using the Atlanta Journal-Constitution's definition, pretty much any forecast random guess will be 50% accurate over time, since the temperatures in February and March are above average half the time and below average half the time.

According to Wikipedia, Punxsutawney Phil has predicted an early spring 13% of the time, so by choosing a broader definition of "winter", it is possible to make him look more accurate.
posted by TedW at 10:15 AM on February 2

I have never really understood the distinction between "six more weeks of winter" (counting from February 2, that's March 16) and an "early spring."

Doesn't spring officially start March 21? So, six more weeks of winter, ending on March 16, would still be an early spring. Thus I always thought Groundhog Day was a six-of-one, half-dozen-of-the-other kind of joke. Unless it means six extra weeks of winter, beyond March 21, an interpretation I have never actually heard anyone articulate and which would move the beginning of spring all the way back to May, Groundhog Day just doesn't make sense to me as anything but a quirky tradition to mark the halfway point between the first (calendar) day of winter and the first (calendar) day of spring and acknowledge most people's hope for an early spring.

Thus it seems like Phil would be wrong every time it is not spring before March 21.

Then again, I live in Michigan and would kill for it be spring beginning on March 16. Or even March 21, for that matter.
posted by isogloss at 12:33 PM on February 2

Link to the Stormfax Almanac record of Mr. Phill's performance back to 1887. And scroll up for the weirder-than-you'd-expect story of why a woodchuck's relationship with its shadow came to predict weather. (Short answer: It's a spectacle made up by the Punxsutawney, Pennsylvania chamber of commerce based on a bunch of arcana.)
posted by Ookseer at 1:18 PM on February 2

isogloss, mid-March is an "equinox." Some people call this the "first day of spring," but people say silly things all over.

If Earth didn't have any atmosphere, the only thing that would determine the temperature would be the day's sunlight: how long the sun is above the horizon, and whether sunlight hits the ground straight on or at an angle. The coldest day of the year would be the winter solstice, a short day where the sun never climbs very high in the sky. The warmest day would be the summer solstice, when the sun is high in the sky for a long time. Back when people needed to guess the weather to grow food, but didn't have good clocks, "midsummer" and "midwinter" were the astronomical events they noticed. If you wanted a three month "winter," centered on "midwinter," it would begin in early November and end in early February.

Of course the earth does have an atmosphere, and also lots of water, which complicates the weather because big masses of air and water and water vapor can take weeks to change temperature. Even though the solar irradiance is the same, early February is colder than early November. More of the fresh springtime February heat goes into the cold stuff left over from January.

So no, spring doesn't really start on the equinox. If you wanted to be consistent with the old names for the solstices, the equinoxes would be "midspring" and "midautumn." But "mid-transition" is a pretty slippery idea — especially if you live far enough north that the transition doesn't obviously get going until mid-to-late March. It isn't as if there's a magic springtime turnon switch ever, anyway; if you're looking for one of those so you can start doing your planting, a groundhog is as useful as anything else.
posted by fantabulous timewaster at 9:01 PM on February 2 [1 favorite has favorites]

Interesting that Phil is apparently 112 years old. Maybe we should ask him about longevity rather than weather.
posted by fantabulous timewaster at 9:02 PM on February 2

This year, from the report I read the guy had to grab that poor sleeping groundhog and hoist him up in the air. Who would see a shadow that way? Personally, I think it's all a pr thing. Where's the humane society when you need them? ;-)
posted by Taken Outtacontext at 9:36 AM on February 3