January 7, 2025
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Freezing temperatures are below normal this week, but “normal” is getting warmer
Blasts of Arctic air have brought much colder-than-normal temperatures to parts of the US, but that “normal” bottom is warmer than in the past.
Louisville Quint 9 firefighters shovel snow in front of their station on January 5, 2025 in Louisville, Kentucky. Local forecasts called for heavy snowfall followed by significant accumulations of freezing rain and ice.
Luke Sharrett/Getty Images
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The conversationan online publication featuring the latest research.
An Arctic blast that hit the central and eastern US in early January 2025 is forming cold conditions in many places Parts of North Dakota were submerged more than 20 degrees below zeroand people as far south as Texas woke up on January 6th to teenage temperatures. A snow and ice storm in the middle of the country the winter cold added to it.
Forecasters warned that temperatures could be “10 to more than 30 degrees below normal” across much of the eastern two-thirds of the country throughout the first week of the year.
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But what does “normal” really mean?
In the meantime temperature forecasts are important to help keep people safe, comparing them to “normal” can be quite misleading. Therefore, what is considered normal in predictions has been changing rapidly over the years as the planet has warmed.
Defining normal
one of the most used standards defining “normal” based on scienceIt is a 30-year average temperature and precipitation. every 10 years National Center for Environmental Information It updates these “normals”, most recently in 2021. The current range considered “normal” is 1991-2020. Five years ago, it was 1981-2010.
But temperatures have risen over the past century, and the trend has accelerated since the 1980s. This warming is fueled by the mining and burning of fossil fuels that increase atmospheric carbon dioxide and methane. These greenhouse gases trap heat nearby to the surface of the planet, causing the temperature to rise.
How temperatures considered “normal” in the US have changed over the decades. Each 30-year period is compared to the 20th century average.
As global temperatures are warming, so is what is considered normal.
So when a cold set in 2025 is expressed as the difference between actual and “normal” temperatures, it will be colder and more extreme than compared to the 30-year average.
Thirty years is an important part of human life. For people under the age of 40, using the last average range can match what you’ve experienced.
But he doesn’t speak how much the Earth has warmed.
How cold today compared to the past
How does today’s cold – or today’s warming – compare to the time before global warming began to accelerate? NASA scientists use 1951-1980 as a basis
The reason is obvious when you compare the maps.
For example, January 1994 was bitterly cold east of the Rocky Mountains. If we compare those 1994 temperatures to today’s “normal” – the 1991-2020 period – the US looks a lot like temperature maps in early January 2025: large parts of the Midwest and eastern US were above 7 degrees Fahrenheit (4 degrees Celsius). below “normal”, and some areas were much colder.
Comparing January 1994 temperatures to the 1991-2020 average, the current 30-year period used to define “normal.”
NASA’s Goddard Institute for Space Studies
But if we compare January 1994 to the 1951-1980 baseline, that cold spot in the eastern US is not as large or extreme.
January 1994 temperatures in some parts of the country were 14.2 F (7.9 C) colder than normal compared to the 1991-2020 average, 12.4 F (6.9 C) compared to the 1951-1980 average.
How January 1994 temperatures compare to the 1951-1980 average.
NASA’s Goddard Institute for Space Studies
As a measure of a changing climate, updating the 30-year average baseline every decade makes the warming appear smaller than it actually is, and the cold snaps appear more extreme.
Conditions for high lake-effect snow
The US will continue to see outbreaks of cold air this winter, but as the Arctic and the rest of the planet warm, the coldest temperatures of the past will not be the norm.
This warming trend is helping to set up the remarkable situation we’re seeing in the Great Lakes in January 2025: heavy lake-effect snow over a large area.
As the cold Arctic air moved in from the north in January, it encountered a Great Lakes basin where the water temp. still over 40 F (4.4 C). in many places Ice covered less than 2% of the lake’s surface on January 4.
This cold dry air causes evaporation over warmer open water, providing moisture lake effect snow. Parts of New York and Ohio were well visible on the lakes on a foot of snow in a few days.
The accumulation of heat in the Great Lakes, which is observed year after year, is affecting it fundamental changes in winter weather and the winter economy in the states bordering the lakes.
It is a reminder of the persistent and growing presence of global warming, even in the midst of a cold air outbreak.
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