The little wintry weather in December in the southeast brought many unusual scenes: crowds filling parks and beer gardens, people wearing short sleeves on Christmas parades, and azaleas in bloom just before the holidays.
Average temperatures were about 6 to 9 degrees above normal and precipitation was well below normal in major cities in the Carolinas. This concordance of predictions of experts this fall. And it can be a sign that we need to change the way we think about a normal winter in the Carolinas.
This year’s mild winter has two main causes, said Andy Pershing, director of climate science at Climate Central, a climate research and communications organization based in Princeton, New Jersey.
First there is La Nina. It’s a weather pattern of the Pacific that pushes the jet stream north – the opposite of El Niño. La Nina usually causes higher temperatures and drought in the southeast.
Then, he said, “We have this general trend of global warming that tends to make things hotter overall, all over the planet,” Pershing said. Global warming trends are most pronounced in winter in the United States, he said.
December in Charlotte is 3.1 degrees warmer than in 1970, according to data from the Climate Central and the National Weather Service. (Graphic below)
Rising average temperatures
The numbers definitely increased in December. Charlotte, where the average high temperature in December is 55 degrees, experienced 26 days above it. This included a near-record high of 78 in December on December 3.
Overall, the city’s average temperature for the month – for 24 hours a day – was 53.2 degrees, 8.5 degrees above normal. This makes it the third hottest December since 1878, Pershing said.
Meanwhile, precipitation of just over 2 inches was 40% less than normal for Charlotte. Similar conditions have much of the Carolinas now in moderate to severe drought.
By normal, we mean the average over the most recent 30-year period, 1991 to 2020. This is how it is defined by experts at the National Oceanic and Atmospheric Administration.
“You look at all the data from that period, and you characterize the temperatures, highs, lows, precipitation, snowfall, all of those things, and that gives you an idea of the climatic conditions that you should expect in a place based on that recent history, ”Pershing explained.
The story was the same in all the towns in the Carolinas. Average temperatures were above normal by 8.8 degrees in Wilmington, 8.7 degrees in Hickory, 8.4 degrees in Greensboro / Winston-Salem, 8 degrees in Raleigh and 7.5 degrees in Greenville / Spartanburg, SC (see the graphic.)
Similarly, precipitation was below average elsewhere, notably in Asheville (-78%), Hickory (-72%), Greensboro / Winston-Salem (-50%) and Raleigh / Durham (-52% ).
A new normal?
Pershing said warmer, drier winters are becoming the new normal for the Carolinas due to climate change, and it gets worse whenever La Nina is a factor.
Comparing a monthly average to the past 30 years may be less helpful now because of the rapid changes over the past 10 years, Pershing said.
“Looking back over the past 10 years, all of those years have been above normal, I believe, except one,” Pershing said. “And that’s very consistent with this general trend that we’re going through. So this idea of a normal climate based on 30-year conditions, and that you can kind of plan that and keep it going, really isn’t. not applicable in some ways in this world with very active climate change. “
“Overall, we would expect each year to be more likely to be slightly warmer than the year before,” he said.
These deviations from normal make it more difficult to plan the weather, infrastructure or even your household.
“A big challenge is that a lot of the planning is done according to the climate normal,” Pershing said. “If you are building a road, the size of culverts and storm sewers is often determined by climatic norms. How much snow you expect determines the building codes for the roofs of buildings.
As the climate changes, Pershing said planning should be based on what we see coming, not just the historic 30-year average.
“One of the things that people in the climate community are really starting to try to defend is to try to use some of these climate projections and build these (building) codes based on the projections, not just on that. that we observed, “he said. “Because we can easily find ourselves in a situation where we’ve basically built to a standard that’s already surpassed us.”
The drought continues
Meanwhile, unusually dry weather and low water levels prompted authorities to declare a zero-level drought watch for the Catawba-Wateree River Basin, which stretches from western Carolina from North to South Carolina.
Stage zero is the lowest of the river’s five stages of drought.
The Catawba-Wateree Drought Management Advisory Group says dry conditions are expected to continue, so they are encouraging water conservation.
The National Drought Monitor, which uses a slightly different scale, shows most of the state in some level of drought. (See map.) An area from Wilkesboro to Hickory to Charlotte and east to the coast was classified as moderate drought on Thursday January 6. This is a slight improvement over the past few weeks.
A version of this story appeared in the WFAE’s weekly climate newsletter, which is emailed every Thursday. Read and subscribe on https://www.wfae.org/sign-up-for-our-newsletters
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