Comparing Winters: How Does This Winter Measure Up?

We doubt anyone has yet forgotten the stretch of single-digit temperatures in January (or has stopped hoping that that’s it for the season and the worst of winter is over). But looking at the data, has this winter actually been colder than the winters of recent years?

This may vary on how we define “winter” for the purposes of the analysis. It sounds like a fairly straightforward concept, but there are actually two options: astronomical seasons, or meteorological seasons.

What’s the difference between astronomical and meteorological seasons?

Astronomical seasons are based on the Earth’s movements around the sun, and are marked by the solstices and equinoxes[1]. They’re what give us the idea that the first day of winter, spring, summer, or fall are on or around December 21st, March 21st, June 21st, and September 21st (the actual dates vary slightly from year to year)[2].

Meteorological seasons are based on the weather[3]. You may have observed, at one time or another, that it seems odd for winter to not technically start until December 21st, when its characteristic associated weather is often in full swing by then. The meteorological seasons reflect this: meteorological winter is defined as December-February, spring as March-May, summer as June-August, and fall as September-November[4]. They include entire months, rather than parts of months, making analysis much easier – the climate data resources we refer to here at CCRPC assess minimum, maximum and average temperature, wind speed, and precipitation by the month, not by the week.

All analysis in this post assumes meteorological seasons. However, it’s good to be aware of the astronomical seasons as well, and how the two differ.

Has this winter been colder than recent ones?

First of all, we can’t actually judge the full season yet – since meteorological winter includes December, January, and February, we don’t have all the necessary data. The last weeks of the season are still to come.

What we can look at is the seasonal data for the December-January period for this year and previous years, shown in the table and charts below. This data comes from the Illinois Climate Network’s Monthly Climate Summary Data source, and was recorded at the Champaign recording station. The Illinois Climate Network is part of the Illinois State Water Survey’s Water and Atmospheric Resources Monitoring Program (WARM).

Table: Maximum, Minimum, and Average December and January Temperatures, 2007-2018Download table data for Maximum, Minimum, and Average December and January Temperatures, 2007-2018.

Source: Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2018). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. http://dx.doi.org/10.13012/J8MW2F2Q. (Retrieved 6 February 2018).

Chart: Maximum, Minimum, and Average Temperatures: December 2007-2017Download chart data for Maximum, Minimum, and Average Temperatures: December 2007-2017.

Source: Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2018). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. http://dx.doi.org/10.13012/J8MW2F2Q. (Retrieved 6 February 2018).

Chart: Maximum, Minimum, and Average Temperatures: January 2008-2018Download chart data for Maximum, Minimum, and Average Temperatures: January 2008-2018.

Source: Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2018). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. http://dx.doi.org/10.13012/J8MW2F2Q. (Retrieved 6 February 2018).

We can quickly pick up on a couple things from the graphs and data above.

First, in a given month, the maximum, minimum, and average temperatures tend to trend together. Of course, there are exceptions to this (e.g., in December 2014, the maximum temperature decreases while the minimum and average temperatures both increase), but it seems to hold true for the most part. Second, January’s maximum, minimum, and average temperatures are usually, but not always, lower than December’s. Most pertinent to our question of whether this year’s two months of winter so far have been colder than recent years’, the answer is it depends on what exactly you’re looking at.

December 2017’s minimum temperature of -3.7 degrees is slightly higher than December 2016’s minimum temperature of -4.6 degrees; these two years have had the lowest December minimum temperatures of our study period. The minimum temperature in January 2018 is tied with that of January 2014, and both are the coldest January minimum temperature since 2009’s -15.5 degrees Fahrenheit.

The maximum temperatures of December 2017 and January 2018 were 65.2 degrees and 59.2 degrees, respectively. This makes December 2017’s maximum temperature the third-highest December maximum temperature of the study period, after 2012 and 2015. This January’s maximum temperature is in the bottom half of its field: five of the study period years had higher January maximum temperatures than 2018.

December 2017’s average temperature was 29.4 degrees, colder than five of the 10 other study years, but warmer than last year, December 2016. January 2018’s average temperature is colder than six of the other 10 study years, and is the coldest on average since January 2014.

So it’s been a cold winter so far, but we can’t say it’s been the coldest by all three measures: maximum, minimum, and average monthly temperature. And like we said, it’s not over yet. Who knows what the rest of February will bring?

Do several mild winters in a row mean you’re due for a harsher one?

The short answer is no.

The longer answer is that weather and climate are extremely complicated; the process of arriving at accurate, well-informed forecasts is not a meteorological game of “duck, duck, goose.” Think about the terms “100-year storm” and “500-year storm.” Those designations don’t mean that a storm of that size will happen once a century, like clockwork; what they mean is that there’s a 1% chance, every year, of such an event occurring (or a 0.2% chance, in the case of a 500-year storm). The fact that that 1% result comes up in a given year has no bearing on the odds of whether it will the following year – the following year, it will still be a 1% chance. And while what constitutes a 100- or 500-year storm can be recalculated (e.g., to be more or less severe, usually in terms of precipitation), this doesn’t change the odds either: a 100-year storm is always defined as the storm that has a 1% chance of occurring each year.

The same principle applies to winter weather. It’s true that weather and climate patterns are deeply interconnected, and that this year’s weather can be said to impact next year’s weather to some degree, as patterns shift and weather systems move and interact throughout the year. However, we cannot say that we will have a cold winter one year because and only because some recent winters have been mild.

Climate modeling is complex – unfortunately, we can’t make it that simple.

 

[1] “Meteorological Versus Astronomical Seasons.” National Oceanic and Atmospheric Administration. National Centers for Environmental Information. (No date). https://www.ncdc.noaa.gov/news/meteorological-versus-astronomical-seasons.

[2] Ibid.

[3] Ibid.

[4] Ibid.

Table and Charts Data Source: Water and Atmospheric Resources Monitoring Program. Illinois Climate Network. (2018). Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7495. http://dx.doi.org/10.13012/J8MW2F2Q. (Retrieved 6 February 2018).

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