Graph: How Cold Has It Been This Winter?

Last week FiveThirtyEight posted an article looking at weather data nationally to assess the notion that this winter was particularly cold. I am quick to caveat such claims as applications of the availability heuristic, so I loved FiveThirtyEight’s analysis to settle with real measurements whether the claim is true.

But even the shiny graphs and rigorous analysis of FiveThirtyEight left me unsatisfied on this issue. That’s because what I really cared about was my local weather. So I dug around and found some data of my own: average and 2013/14 high and low temperatures for my home of Amherst, Massachusetts.

Highs and Lows: Average vs Actual

amherst temperature actuals

First a note: I like using highs and lows rather than daily average temperatures because they feel more real to me. The temperature oscillated between these bounds on that day, but how long was it actually at that specific average temperature? That said, my results are going to resemble those I would have gotten had I used averages, so it’s not super important in this case.

The above graph is pretty messy, so we can’t really answer the question with it too well. So I made another one:

Moving Weekly Average of Deviation from Temperature Norm

Amherst temperature averages

This one can answer the question. Yes, it has been cold. Especially since late January, but also multiple times this winter before that as well.

To make this, first I subtracted the average highs and lows for each day from the actuals. For each day, this number showed me how many degrees warmer or colder it got than the mean. I then averaged these variance numbers together to get a composite number (see, doesn’t that look like average temperature?) measuring what the mean variance was from high and low temperatures. Finally, I took the moving average for each day and the three days before and after it. I did this because our perceptions of what the weather is like are influenced not only by what’s going on in the moment, but also what’s happened recently and what’s in the forecast.

The result, as you can see, shows us bizarrely cyclical trends in temperature this winter. Every 2.5 to 3 weeks, we see this measure of temperature variance cycle back to another peak or valley. I can’t think of any methodological error that would distort the results in this way (except maybe the moving average, but that shouldn’t regulate such long stretches of time), and have no reason to believe the source data are wrong, so my best guess is that it’s coincidental.

Presuming my methodology is sound, this is just the sort of graph I was looking for to explain what the temperature was like this winter. I hope you find it interesting as well.