Monday, February 4, 2013

Groundhog Predictions

This past Saturday (February 2) was Groundhog Day, a day of anticipation by many tired of winter.  Each year people wait to see what the groundhog has to say about the coming spring.  The most famous groundhog is Punxsutawney Phil in Pennsylvania and has the longest running record.  Predictions from 1888 to 1900 were intermittent and became regular after that time.

Punxsutawney Phil comes out of his hole each Groundhog Day, like clockwork, to tell us if we can expect an early spring or another six weeks of winter. If Phil sees his shadow, he’ll go back underground to wait out the next chilly month and half. If there’s no shadow, Phil — and the rest of us — know that spring is right around the corner.

Average temperature for Columbia, SC, from February 2 - March 16.  Image Credit: Climate Central.

The six-week period that starts on February 2nd has been getting gradually warmer in Columbia since 1887. The warming hasn’t been uniform: you can see from the graph above that some years are cooler than average and some are warmer, but the overall trend is slowly upward. This is consistent with the rising global temperatures that climatologists have predicted with increasing certainty for decades.
It is hard to take any of this seriously, but it is interesting to look at the predictions.  Plus it is just fun to anticipate what the groundhog will do.

Phil's forecast of an early spring.  Image Credit: Climate Central.

If you plot Phil the Groundhog’s historical predictions against temperatures, it almost looks like the furry forecaster is on to something. Each line represents a year when he predicted spring would come early. As you can see in the chart above, he’s gone for a long winter and a late spring most of the time. However, in recent years, he’s been calling for an early spring more and more frequently — and sure enough, spring temperatures have been rising over that same period.

The average temperature for Columbia for the six weeks starting February 2 vs Phil's forecast of an early spring.  Click here for an interactive graph.  Image Credit: Climate Central.

Furthermore, when you plot his calls for an early spring against the record for Columbia, you find that he has been right half the time.  That’s about as good as a coin toss.

Phil’s reputation has given rise to other groundhog soothsayers.  Here in the South there is General Beauregard Lee in Georgia, Chattanooga Chuck in Tennessee, and Sir Walter Wally in North Carolina.  Each one purporting to know what is ahead for spring.

Here are the predictions for 2013:

          Punxsutawney Phil                       early spring
          General Beauregard Lee              more winter
          Chattanooga Chuck                      early spring
          Sir Walter Wally                            more winter

So, there you have it for 2013.