Groundhog Day
In western countries in the Northern Hemisphere the official first day of Spring is about six weeks after Groundhog Day, on March 20 or 21. About 1,000 years ago, before the adoption of the Gregorian calendar when the date of the equinox drifted in the Julian calendar, the spring equinox fell on March 16 instead. This was exactly six weeks after February 2. Assuming that the equinox marked the first day of spring in certain medieval cultures, as it does now in western countries, Groundhog Day occurred exactly six weeks before spring. Therefore, if the groundhog saw his shadow on Groundhog Day there would be six more weeks of winter. If he didn't, there would be 42 more days of winter. In other words, the Groundhog Day tradition may have begun as a bit of folk humor.

Alternatively, the custom could have been a folk embodiment of the confusion created by the collision of two calendrical systems. Some ancient traditions marked the change of season at cross-quarter days such as Imbolc when daylight first makes significant progress against the night. Other traditions held that Spring did not begin until the length of daylight overtook night at the Vernal Equinox. So an arbiter, the groundhog / hedgehog, was incorporated as a yearly custom to settle the two traditions. Sometimes Spring begins at Imbolc, and sometimes Winter lasts 6 more weeks until the equinox.

In Canada
Wiarton Willie is a famous Canadian groundhog who lives in the community of Wiarton in Bruce County, Ontario. Every February 2, on Groundhog Day, Willie takes part in the local Wiarton Willie Festival. His role is to predict whether there will be an early spring. Although the original Wiarton Willie died in 1999, the Wiarton groundhog day celebrations continue each year with the original Willie's successors, referred to as "Wee Willie."

Groundhog Day, featuring Wiarton Willie, is a popular annual festival in Wiarton and is similar to events in other locations in North America. A midwinter celebration involving an animal with predictive powers was an element of Celtic culture. The link between weather prediction and the day is said to have been inspired by an old Scottish couplet: "If Candlemas Day is bright and clear/ There'll be two winters in the year."

The story of Wiarton Willie dates back to 1956. A Wiarton resident named Mac McKenzie wanted to showcase his childhood home to his many friends, so he sent out invitations for a "Groundhog Day" gathering. One of these invitations fell into the hands of a Toronto Star reporter. The reporter travelled to Wiarton looking for the Groundhog Day event. None of the townspeople knew about a festival, but one suggested he check at the Arlington Hotel, the local watering hole. There the reporter found McKenzie and his friends partying and was invited to join them. The next day, the reporter lamented to McKenzie that he needed some kind of story to take back to justify his expenses. So McKenzie grabbed his wife's fur hat, which had a large button on the front, went out to the parking lot, dug a burrow in the snow and pronounced a prognostication (which no one remembers). The picture of Mac and the hat ran in the February 3, 1956 edition of the Toronto Star. A year later, about 50 people arrived for the festival. Half were reporters from various media, including the CBC and Canadian Press. Seizing on the opportunity, McKenzie invented a festival that has been added to over the years.

Wiarton Willie himself is a more recent addition to the festivities. In the early years, prognostication was provided by the "mythical" trio of groundhogs Grundoon, Muldoon and Sand Dune. Willie appeared on the scene in the 1980s. Wiarton Willie's predictive powers are attributed (by his followers) to his situation on the 45th parallel, exactly halfway between the Equator and the North Pole. He is claimed locally to be accurate in his prognostications around 90 per cent of the time, although scientific studies show groundhog predictions to have a success rate of more like 37 per cent.