Sustainability Climate Change

Thanks to heat waves the lower 48 could see warmest December yet

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Power lines in Los Angeles, California on September 3, 2020, ahead of a heatwave to arrive September 4 through the Labour Day weekend prompting a statewide flex alert. FREDERIC J. BROWN/AFP via Getty Images)

Story at a glance

  • The National Weather Service published a series of maps predicting unprecedented above-average temperatures for huge swaths of the country.
  • The heat wave will affect the upper Midwest and Southern states.
  • From Dec. 14 through Dec. 20, there’s a 90 percent probability of above normal temperatures for about half the country.

Large swaths of the country are expected to experience a record heat wave just as the winter season officially begins, a consequence of climate change.

The National Weather Service (NWS) released projections from its climate prediction center that shows states in the Southeast experiencing above normal temperatures from Dec. 18 through Dec. 22. That heat wave will expand quickly, with predictions for Dec. 20 through Dec. 26 indicating at least 20 states will have above normal temperatures for that time period.

The most extreme ends of the heat wave will concentrate in Florida, Georgia, Alabama and Mississippi, with a 70 to 80 percent chance of above normal temperatures, according to the National Oceanic and Atmospheric Administration (NOAA). 

Brian Brettschneider, a climatologist from Alaska, tweeted that the NWS map for Dec. 14 through Dec. 20 indicated a 90 percent probability of above normal temperatures on any eight- to 14-day outlook period since 2015.  

“It’s time to stop celebrating above normal winter temperatures. Every cold day we can squeeze out of our warming world keeps the planet liveable [sic] a little while longer,” tweeted Brettschneider.


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Only a small sliver of the country is predicted to have normal temperatures in December, with NOAA’s map indicating only certain sections of Arizona, Utah, Wyoming and states in the upper Midwest to be in “near normal” temperatures. 

That means for many states across the U.S., a white Christmas is not likely.  

Though meteorologists say the warmer temperatures are due to a number of factors, high pressure in the Pacific near the international date line has been responsible for a drop in the offshore jet stream in the West Coast and between Alaska and Hawaii, according to The Washington Post.

That jet stream has also come Northeast, allowing warmer temperatures to build over the Northern Rockies and upper Midwest. It also causes the winds over the central U.S. to downslope. That leads to warming and drying.

Human-induced climate change also plays a role, with activities that emit greenhouse gases causing the atmosphere to warm too.

As the Earth continues to warm, unusual temperatures throughout the year will become increasingly common and intensify in magnitude. 

According to the U.S. Environmental Protection Agency (EPA), the trend in multi-day extreme heat events across the U.S. has consistently gone up from the 1960s all the way to the 2010s. Heat waves in the U.S. have increased so much that the average of two heat waves per year during the 1960s has gone up to six per year in the 2010s. 

“Of the 50 metropolitan areas in this indicator, 46 experienced a statistically significant increase in heat wave frequency between the 1960s and 2010s,” said the EPA.


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