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  • Accuracy of Groundhog Predictions

    Mr. Murray's 7th Grade Students
    Dolphin Senior Public School
    Mississauga, Ontario
    rodmurr@astral.magic.ca

    "If Groundhog Day be fair and bright,
    Winter will have another flight,
    But if Groundhog Day brings cloud and rain,
    Winter is gone and won't come again."

    From the legends, the groundhog comes out from its burrow exactly at noon on February 2nd to look for its shadow. If it is a sunny day and the groundhog sees its shadow it goes back to his hole to sleep, and winter continues for 6 more weeks. If it doesn't see its shadow it stays outside because spring is just around the corner.

    The shadow part is true because sunny days in winter are associated with colder, drier arctic air, and cloudy days with milder, moist maritime air. The weather on any February 2nd may continue for a few days, but usually no longer than that.

    Groundhog Day organizers brag that their groundhog forecasts are 70 to 90 percent accurate, but meteorological records prove that the groundhog's success rates are pretty low. Dr. Philips study of weather data for the past 30 to 40 years for 13 cities across Canada shows that there was an equal number of cloudy and sunny days on February 2nd. During that time, the groundhog's predictions were, on average, 37 percent accurate. For nearly two-thirds of the years the groundhog's predictions were wrong. Given that 33 percent accuracy can happen by chance, an average of 37 percent is not a lot.

    February 2nd has been celebrated in folklore for centuries as the day to look forward to spring. In medieval Europe, Groundhog Day was known as Candlemas Day, a Christian festival named for the custom of lighting candles on that day. In Germany there is a saying that a shepherd would rather see a wolf enter his stable than the sun on Candlemas Day. In France, folks warn that a sunny Candlemas Day means another winter is on the way, while in Spain, a wet February 2nd means the winter is over.

    Groundhog Day began as Hedgehog and Badger Day, but when settlers came to North America they couldnít find hedgehogs, and since the behavior of the groundhog is so similar to the hedgehog they substituted hedgehogs for groundhogs. Since the groundhogs got the role of predicting spring, the name was renamed after them.

    Early settlers hoped for signs of an early spring so they could begin planting and shorten the time to harvest. They wanted the groundhog to emerge and stay out as a prediction to spring. But these settlers did not realize that the groundhog sleeps later than European hedgehog and is unlikely to come out of its burrow in the middle of winter on February 2nd. According to groundhog expert and zoology professor Dr. Edward Bailey of the University of Guelph, when the adult male groundhogs finally emerges from its burrow, the first thing it does is look for a mate. So the Groundhog Day legend is superstition! But we can still celebrate that winter is at least half over!!

    Here are the results of David Philip's study. On the left are the chances of a groundhog seeing its shadow over the past 40 years in major Canadian Cities. On the right is the percentage of correct forecasts that would have been made if the groundhog had seen its shadow based on weather records over the same time period.

    GROUNDHOG FORECASTS MAJOR CITIES CHANCE OF GROUNDHOG CORRECT GROUNDHOG IN CANADA SEEING IT'S SHADOW FORECASTS (PERCENT) (PERCENT) St. John's 53 41 Charlottetown 50 41 Halifax 50 42 Fredericton 48 34 Montreal 52 36 Toronto 54 29 Ottawa 48 42 Winnipeg 78 30 Regina 63 38 Edmonton 60 26 Vancouver 23 35 Whitehorse 43 42 Yellowknife 50 50 Acknowledgements:
    We like to thank David Phillips for the information he has sent us. He is a Senior Climatologist with Environment Canada's Atmospheric Environment Service and is Canada's most popular weatherman. He has written the Weather-wise column for Canadian Geographic magazine for six years and is the originator of Environment Canada's Canadian Weather Trivia Calendar. He also appears on Canada's Weather Network in the "Ask the Expert" program. He also wrote a book about Canadian weather and climate called "The Day Niagara Falls Ran Dry!"