Weather Lab Woolly Bear: Average winter?

I came across this little guy today on the Huttner Weather Lab driveway.

Does the season’s first woolly bear caterpillar have a message about the upcoming winter?

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Woolly bear on the Huttner Weather Lab deck today.

(Photo by Paul Huttner. Click for bigger image)

According to weather folklore, woolly bears can predict the severity the coming winter. The only fly in the woolly bears ointment is that science does not support the notion of the woolly bear as a predictor of winter weather.

The theory in folklore goes like this: The wider the brown band on woolly bears, the milder the winter. A narrow brown band with more black means a more severe winter.

Scientists have studied woolly bears to try and correlate the thickness of the bands with winter weather. The results show that woolly bears have bands of different lengths in the same year, in the same area. So it appears there is no way to use the woolly bear as a predictor of winter forecast.

NOAA’s Climate Prediction Center outlook for winter favors chances for a colder than average winter in much of the Dakotas and northern Minnesota. Water temperatures in tropical Pacific Ocean have cooled this summer, and La Nina conditions have taken over. CPC’s La Nina advisory forecasts a moderate strength La Nina this winter.

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La Nina winters tend to statistically favor average to colder than average conditions in Minnesota, along with higher than average snowfall in the north.

I moved our resident woolly bear onto the weather lab deck for a closer look and a few photos. He was cooperative, but seemed ready to move along after a short time, so I put him back where I found him after the mug shots.

Depending on how this guy stretched out it looked to my eye like he had a medium width brown band, with plenty of black. The non scientific folklore forecast would seem to my eye to indicate an average winter ahead. What do you think?

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The Twin Cities recorded a below average 40.7″ of snowfall last winter, and recorded the first snowless March in modern records. Average annual snowfall for the metro is a respectable 55.9″ for the 30 year period from 1971-2000.

Just seeing the woolly bears move around this time of year as they seek out their winter homes is a sure sign that fall is here, and that winter is (gulp!) around the corner.


  • Chris

    While I was walking in Afton State Park this past weekend I saw a cream-colored wooly bear caterpillar. My first thought, of course, was “What the heck kind of winter does that predict!”

  • Brian

    I’ll second Chris’s find. I was out running the other day and saw one that was totally brown.