Is the weather really abnormally cold? That depends on which years are used as a baseline for 'normal.'

When winter fills the air with cold and bone-chilling gusts, and ice and snow bow down even the sturdiest looking of evergreen branches, it's easy to think that the weather is so much colder than normal. But is it? Using what's "normal" compared to what isn't normal can be confusing. "While temperature forecasts are important to help people stay safe, the comparison to normal can be quit misleading," writes Richard B. Rood for The Conversation. "That’s because what qualifies as normal in forecasts has been changing rapidly over the years as the planet warms."

Who determines what normal temperatures are? "One of the most used standards for defining a science-based normal is a 30-year average of temperature and precipitation," Rood explains. "Every 10 years, the National Center for Environmental Information updates these normals, most recently in 2021."

Over the past century, the planet's temperatures have increased. Rood writes, "Because global temperatures are warming, what’s considered normal is warming, too. So, when a 2025 cold snap is reported as the difference between the actual temperature and normal, it will appear to be colder and more extreme than if it were compared to an earlier 30-year average."

How U.S. temperatures considered normal have changed over the decades. Each 30-year period is compared to the 20th-century average. (NOAA Climate.gov graphic via The Conversation)

To get a better picture of our warming planet, "NASA scientists use 1951-1980 as a baseline," Rood explains, "The reason becomes evident when you compare maps. For example, January 1994 was brutally cold east of the Rocky Mountains. If we compare those 1994 temperatures to today’s normal – the 1991-2020 period – the U.S. looks a lot like maps of early January 2025’s temperatures: Large parts of the Midwest and eastern U.S. were more than 7 degrees Fahrenheit below normal, and some areas were much colder. . . . But if we compare January 1994 to the 1951-1980 baseline instead, that cold spot in the eastern U.S. isn’t quite as large or extreme."

Despite global warming, cold air outbreaks will continue, "but as the Arctic and the rest of the planet warm, the most frigid temperatures of the past will become less common," Rood adds.