Not too long ago, groundhogs across the United States were pulled from their burrows and expected to see or not see their shadows. The most famous, Punxsutawney Phil, did see his shadow and predicted six more weeks of winter. Given the humor in expecting a rodent to produce a seasonal forecast for an entire country, it’s easy to ignore such a thing…especially if you don’t like the outcome. But could he be right for the wrong reason? And why do we do this anyway?
A good question to ask about the idea of six more weeks of winter is “what is the basis for that prediction?” and the answer isn’t as random as it seems. Intertwined with Groundhog Day is the Christian celebration of Candlemas on February 2, started in Europe. A traditional saying about Candlemas in northern Europe is this:
Winter will have another fight.
If Candlemas Day brings cloud and rain,
Winter won’t come again.
There are grains of truth in this—fair conditions in northern Europe tend to imply cold temperatures brought from Siberia, while clouds and precipitation imply warmth brought from the Atlantic. Both of these can be tied to something called the North Atlantic Oscillation, a measure of how wavy (usually colder) or not (usually warmer) the wind pattern well above the ground in Europe is. That pattern is something that tends to favor one state more often than the other much of winter, so there is some chance that early February is a preview of the rest of February and March.
Bringing this to the United States frays the connections—some areas can have many fair and warm days (more likely in the Plains and west of the Rockies), while clouds can be tied to cold (lake effect snow areas know this well). The Northeast is closest to and most affected by the North Atlantic Oscillation, but what predictive ability there is left here or in Europe is effectively removed by reducing the observation to one time on one day. Nonetheless, northern Europeans migrating to the United States many years ago did bring the tradition and chose the US-native groundhog as the mascot of this day.
Still, everyone is left wondering whether there will be an early start to spring and warmer temperatures. No one—human, marmot, or other—can tell with total accuracy. That being said, our best assessment is that the answer is ‘yes’ spring will arrive earlier to the South and West, but not in the Midwest and Northeast. That doesn’t mean that there can’t be a few cold days in the South or West, but it looks like temperatures in February and March are more likely to be warmer than normal overall. For the Midwest and Northeast, conditions will be colder than normal overall—but a warm break or two can’t be ruled out. Keep in mind that ‘normal’ here refers to the 1981-2010 average temperature through the next six-weeks.
Why will it be cold in the north and warm south? If you read “Why Is It So Cold?”, you may remember that the polar vortex in early January was only nudged off the North Pole toward us. This time, it appears a full-on split of the polar vortex is underway with one piece ending up in Canada and the other in Russia. Having a piece of the polar vortex right next door makes it more likely for cold air to be able to push south into the northern US. On top of that, we are still in a weak La Niña that favors warmer conditions in the Southeast, something that tends to become stronger later in winter. As for the West, we expect a continuation of the general pattern so far this winter to keep conditions generally warmer and drier than normal there.
Overall, it looks like Punxsutawney Phil had it half right.