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Ask the Weather Guys: How good are the groundhog predictions?

February 4, 2019

Q: How good are the groundhog predictions?

A: The predictions made by this folk forecast are correct only about 40 percent of the time — vastly inferior to what is delivered by modern science. If you flip a coin, you’ll be right close to 50 percent of the time.

This year’s prediction by the furry animal is for an early spring. As for a more scientific approach, temperatures over the next six weeks look about average.

The forecast made on Groundhog Day is an example of predicting the weather based on folklore. If the groundhog comes out of its hole and sees its shadow, we are in store for 40 more days of winter.

Long before computers, the Weather Channel and the internet, humans needed weather forecasts. Farmers and sailors particularly needed to know if storms were approaching. Over time, various folklore forecasts, often in the form of short rhymes, were devised and passed down through the generations.

Although memorable, the folklore forecasts are of uneven quality — some good, others bad.

The roots of Groundhog Day go back to the 6th century. Feb. 2 is 40 days after Christmas and is known as Candlemas. On this day, candles that are used for the rest of the year are blessed. This is also about the midpoint in winter, in meteorological not astronomical terms. The forecast rhyme goes:

If Candlemas Day is bright and clear

There’ll be two winters in that year;

But if Candlemas Day is mild or brings rain,

Winter is gone and will not come again.

If the day is bright and clear, the groundhog “sees” his shadow and we have more winter. Of course, after Feb. 2, there are only 47 days left of astronomical winter — which ends on or about March 21, so the forecast accuracy should be more than luck.

Of course, the weather conditions on Feb. 2 at single locations like Sun Prairie or Punxsutawney, Pennsylvania, tell us very little about the weather for the rest of the winter season. Right or wrong, they are fun community celebrations.

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