What is Groundhog Day and do the forecasts work?

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What is Groundhog Day and do the forecasts work?
groundhog sits upright on rocky surface

Groundhog photo from Shutterstock

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.

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 forty more days of winter. Of course, after February 2, there are only 47 days left of astronomical winter – which ends on March 21.

The roots of Groundhog Day go back to the 6th century. February 2 is forty days after Christmas and was known as Candlemas. On this day, candles that were used for the rest of the year were blessed. February 2 is also about the mid-point 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, the weather conditions on February 2 at single locations like Punxsutawney, PA or Sun Prairie, WI tells us very little about the weather for the rest of the winter season. As for accuracy, predictions based on the groundhog’s shadow are correct about 40% of the time, vastly inferior to what is delivered by modern science. Right or wrong, they are fun community celebrations.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.