The myth goes that if a groundhog sees his shadow on Feb 2, six more weeks of winter are yet to come, but if he doesn't, spring is just around the corner.

I am wondering if there is any science behind this myth, or perhaps an origin based on observations of actual weather patterns relating to the seasons.

Never mind the groundhog, I am thinking about sky conditions and the seasons.

Specifically, where I am in southern Ontario Canada, winter is usually at its coldest around the start of February. At this time of year we are often under an arctic high pressure "dome"; skies are often clear. As the cold gives way to milder weather, we often end up under the jetstream, or at least it sweeps back and forth over us, delivering a lot of stormy, wintry weather, after which the jetstream at the boundary of the polar air mass eventually retreats north and spring arrives.

Is this an oversimplification? If not, could this sort of pattern be the origin of the myth: generally clear skies mean winter remains settled in, more unsettled weather means winter is about to give way to spring?

  • $\begingroup$ The thing In the end, if there were something directing them to form the idea, then it should show some skill (it should do better than wild guessing). [This graphic from NOAA](This image highlights that skill isn't shown. $\endgroup$ Commented Feb 26, 2018 at 2:13
  • $\begingroup$ (Maybe not enough to be a full answer, but offers a starting point. Perhaps some information on sky condition patterns in PA (and versus Phil). Also note that there are... a lot of "groundhogs" now! But I figure you'd be looking towards the oldest one [Phil???]. $\endgroup$ Commented Feb 26, 2018 at 2:15
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    $\begingroup$ Not an answer, but kind of a fun read: fiftyisthenewfifty.com/the-real-science-behind-groundhog-day The next time somebody wishes you happy groundhogs day, you can say "Happy cross-quarter day to you too". It's also Fred Flintstone's birthday. $\endgroup$
    – userLTK
    Commented Feb 26, 2018 at 5:22
  • $\begingroup$ The way I heard it, Groundhog Day weather is the opposite of the weather to follow: if it's sunny, groundhog sees shadow + winter continues. If it's cloudy, groundhog doesn't seem shadow + winter ends. Also, I metaphysically object to Fred Flintstone have a birthday on a day that couldn't possibly have existed on his calendar :P $\endgroup$
    – user967
    Commented Feb 26, 2018 at 21:36
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    $\begingroup$ @userLTK Yeah, the author kind of makes the point of my question, but makes a couple of horrible mistakes by calling the nominal dates Dec 21 and Jun 21 "equinoxes" (as well as solstices) and the nominal dates Mar 21 and Sep 21 "solstices". There are NOT 4 solstices in the year. Solstice - "sun stand still" - mid-summer and mid-winter! Equinox - "equal night" - day and night same length - spring and fall! Someone needs to correct him! $\endgroup$
    – Anthony X
    Commented Feb 27, 2018 at 2:31

2 Answers 2


It is a myth. To say that it is unscientific is perhaps not the best phrasing, but Groundhog day isn't the most accurate prognostication method around. For something to be scientific, it needs to follow the scientific method. Given that Groundhog day follows the myth that:

  • A groundhog that sees it's shadow will become frightened, seeking shelter from the upcoming chill of 6 more weeks of winter, or
  • A groundhog that doesn't see it's shadow is certain that a chill is not on its way

, the implication derived from a poem being that nice weather now means bad weather later and vice-versa. Without defining 'winter' or 'spring' I question the testability of the hypothesis. In reality, astronomical spring occurs 6 weeks and 4 days after Groundhog day, making the distinction between the groundhog's "definition" of spring entirely subjective. But translating a subjective metric into an objective criteria, it is less accurate than the Farmer's Almanac of 50%.

If you want a more likely explanation on why a groundhog might behave the way it does, one need not look much farther than a picture from Punxsutawney, PA on groundhog day:

Groundhog day, 2020 in Punxatawney PA, source: PennLive.com

Given such a crowd, will an animal react more about the crowd or the upcoming weather? My guess is that if you saw such a crazed crowd show up to your house at 7:25 AM, you would want to crawl into a hole too. A groundhog must go into it's hole at some point, and I don't know of a part of the myth that says that the groundhog must immediately go back into its hole. Doing a groundhog day tradition with so much festivity, scientifically (not necessarily rationally though), be a contaminating factor to any sort of experiment. That is, even slight deviations in how such a thing is conducted (and given that groundhogs like Phil basically live like royalty in comparison to groundhogs in their natural state) make any rigorous evaluation of Phil's prognostication ability questionable.

  • $\begingroup$ Setting aside the tradition of Imbolc and prognosticating rodentia, I am trying to focus on a question about atmospheric conditions on or about the date in question. The premise centers on phenomena like arctic high-pressure domes, unsettled weather under the jetstream, and the seasonal north/south shift of the jetstream (generally speaking) - that clear skies suggest a still-entrenched arctic dome, whereas cloudy skies herald its northward retreat and the imminent arrival of spring weather, and Groundhog day was just a whimsical way to express the phenomenon. $\endgroup$
    – Anthony X
    Commented Apr 14, 2021 at 22:10

Groundhog day doesn't have anything to do with science. It's based on a pagan festival called Imbolc. It's their traditional start of spring and known to Christians as Candlemas.

https://en.wikipedia.org/wiki/Imbolc https://en.wikipedia.org/wiki/Groundhog_Day


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