Groundhog Day Statistics

 Since the 1880's, Punxsutawney Phil has been predicting the weather for the remainder of the winter across the United States. If Phil sees his shadow, we're told to expect 6 more weeks of winter; if not, spring is just around the corner. So, just how well does the groundhog do predicting the onset of spring for southeastern South Dakota?


 Image from


The following table lists the average February temperature and average February snowfall for Sioux Falls, Huron, and Sioux City during all years when Phil has predicted 6 more weeks of winter (Late) and an early spring (Early). The "Sig?" row details whether or not the difference between late and early is statistically significant at a 90% confidence level, and the "t-val" row lists the t test statistic for each location.


  Sioux Falls      Huron        Sioux City    
  Temp (F) Snow (in) Temp (F) Snow (in) Temp (F) Snow (in)
Late 20.4 8.4 19.5 8.8 24.0 6.3
Early 20.3 6.2 20.3 7.3 24.6 7.1
Sig? No No No No No No
t-val 0.055 1.250 -0.374 0.733 -0.361 -0.391


The prediction for 2011 is an early spring, but it looks like Phil isn't too accurate for Sioux Falls and the surrounding areas. However, in the Northern Plains, spring seems early whether it's just around the corner or 6 weeks away.

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