Charting Connecticut is a regular feature produced by the CT Mirror's data team that looks at Connecticut through a quantitative lens.
People across the state either celebrated or lamented the lack of snow last winter. But was it a one-time event or part of a longer trend? One way to find out is by looking at heating degree days, which measures heating requirements over the course of the winter season.
Despite its name, a heating degree day isn’t a measure of days. It’s the difference between 65 and the day’s average temperature (when it’s colder than 65), and they accumulate through the winter season. For example: If the average daily temperature on a given day is 25 Fahrenheit, 40 degree days (65-25=40) will be added to the year’s total. The more heating degree days, the more heat energy will be needed.
The energy industry tracks it for heating demands and the agriculture industry for farming. Over the last few decades, the average season, which runs from the beginning of July to the end of June, has had about 6,000 degree days in central Connecticut.
But last year, that changed dramatically.
We obtained the average daily temperatures in Connecticut for every day since the 1950s from a weather station at Bradley International Airport, calculated the daily number of degree days, totaled them per season and compared them to find the coldest.
The 2022-23 winter season, which ended in June, was the second-warmest in Connecticut since 1950.
The 2022-23 season had 4,994 degree days, compared to an all-time high of 7,015 in 1959. That means that in 2022-23, there were about 2,000 fewer degree days than in 1959.
And the year-to-year variation is normal.
“Anything that impacts temperature will impact the degree days. El Niño and La Niña can impact temperatures in the Northeast, typically in winter, as well as storm systems, the jet stream location, large scale oscillations, as well as cloud cover,” said Jessica Spaccio, a climatologist with the Northeast Regional Climate Center.