Groundhog Day

What the day is

Groundhog Day is observed on February 2. A groundhog emerging and seeing its shadow is said to mean six more weeks of winter, and no shadow means an early spring.

Origin and background

The date is Candlemas, which carried weather prophecy in European tradition long before any animal was involved, built on rhymes holding that a bright, clear Candlemas foretold a long winter while a dull one promised spring. German communities attached the tradition to a hibernating animal, originally a hedgehog or badger, and German-speaking settlers in Pennsylvania transferred it to the groundhog, which was locally abundant. The organized celebration at Punxsutawney dates from the 1880s.

The prediction has been tested, which is the part usually left out. Meteorological agencies and researchers have compared the recorded verdicts against subsequent temperature data across many decades, and the accuracy lands around chance, in some analyses slightly below it. Occasionally a run of hits gets publicized; over the long record there is no skill. The underlying logic does not survive scrutiny either, since a single animal's behavior on one morning in Pennsylvania has no bearing on continental weather six weeks out.

The folklore has a kernel of sense, mind. A bright clear early February in that region often indicates high pressure and cold dry air, while overcast conditions can mean milder maritime air. It is a real local signal for the next few days, stretched into a seasonal forecast it cannot support.

The groundhog itself is a marmot, the same genus as the alpine animals, and a true hibernator that would not naturally be above ground in early February at all.

How to take part

• Watch the ceremony and enjoy it as folklore rather than forecasting.
• Look up the accuracy studies, which are short and conclusive.
• Read the Candlemas weather rhymes it descends from.
• Note that the animal is a marmot, and a genuinely impressive hibernator.
• Check an actual seasonal outlook if you need one.