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December Was Likely the Hottest on Record for the U.S.

The weather wasn't just wild, it was also incredibly hot across large parts of the Lower 48, leading to what is likely a new national record.

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A home burns after a fast moving wildfire swept through the area in the Centennial Heights neighborhood of Louisville, Colorado, against a darkening sky.
A home burns after a fast-moving wildfire swept through the area in the Centennial Heights neighborhood of Louisville, Colorado.
Photo: Marc Piscotty (Getty Images)

December 2021 can now add another dubious superlative to the weather record books. Preliminary data indicates it was the hottest December ever for the Lower 48.

The last month of 2021 featured some form of nightmare weather for nearly every corner of the country, but the stark heat record shows December was more than a rolling series of catastrophes. It was downright hot for all but a few slivers of the continental U.S.

The month ended roughly 5 degrees Fahrenheit (3 degrees Celsius) hotter than normal, according to weather station data from across the country. (Normal, in this case, is the period from 1991 to 2020.) That would surpass the record set in 2015. Scientists at the National Oceanic and Atmospheric Administration still have to crunch all the data for it to be official, but it seems likely that 2021 will come out on top given that preliminary data indicates it was nearly 1 degree Fahrenheit (0.6 degrees Celsius) hotter than the 2015 record.

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Some regions were dramatically warmer than the average. Like, really dramatic. Texas was an astounding 10 degrees Fahrenheit (6 degrees Celsius) hotter than the 20th-century average. That type of heat averaged over such a large area for a week would be shocking, but it’s truly staggering for a month. December 2021 was Texas’ hottest in 130 years of records, crushing a record set during the Dust Bowl in 1933. It’s also the first time Texas has ever had any month more than 10 degrees Fahrenheit above the 20th century average, according to Texas state climatologist John Nielsen-Gammon.

“Global warming didn’t cause this December to be record-setting, but it did contribute to the margin of victory,” he said in a statement.

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Numerous other weather stations in the South and Midwest also reported record heat with large parts of the Southeast and Mid-Atlantic having a December that ranked among the top two or three hottest on record. Only a few pockets of the West saw cooler than normal temperatures. Another way to understand just how hot it was is by looking at daily record highs versus lows. While the last few days of data still haven’t been released by NOAA, the past 30 days that they do have on file show highs outpacing lows by a 5-to-1 ratio. Put simply, it’s been too damn hot for December.

Extreme heat in all seasons is one of the clearest signs of climate change, and winter is generally the fastest-warming season for the eastern half of the U.S. While the absolute temperatures in December might not be as eye-popping as, say, what happened in the Pacific Northwest this past summer, that doesn’t make them any less astounding.

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The extreme heat also helped drive some of the nightmare weather across the U.S. It was a key ingredient in the deadly tornado outbreak and dust and wind storm that swept through the country in mid-December. The heat also left normally snow-covered areas naked. That includes eastern Colorado, where horrific wildfires lit up in late December and burned through nearly 1,000 structures as part of a never-before-seen urban firestorm.