Annual Average Temperatures in Burlington

It's the start of another year in Burlington with no snow on the ground and none forecast in the near future.  NOAA provides a ton of weather data and so I downloaded some Burlington, VT weather data in CSV format.  The data I used comes from two stations, one for measurement prior to 1940, and data from the Burlington International Airport since 1940.

A quick scatterplot shows the average temperature in degrees Fahrenheit by year.  The years start with 1902 and go to present day.  The average yearly temperature ranges from about 42 to 50.  Obviously, average daily temperatures for individual days within every year have a much wider range; looking at the average yearly temperature is a useful first look at long-term trends.  Just by eyeballing, it certainly looks like there is a decades-long upward trend from the 60's to today, and a typical day in 2020 is 8 degrees warmer than a typical day in 1960.  That could easily be the difference between a January with snow cover and a January with bare ground.  

Fitting a best-fit line to the data helps us to see that long-term upward trend: 

... though a quick examination of the residuals confirms that the straight line is not a great model here.

A third-order polynomial does a much better job of capturing the initial stability, followed by an upward rise in temperatures.  A piecewise spline might be even better, but this is enough for a first quick look.  

Next steps might be to look at how the temperatures change over time for each day of the year, or look at the snow depth data.