December's un-wintry weather across the Southeast brought lots of unusual scenes: Crowds packing parks and beer gardens, people wearing short sleeves to Christmas parades and azaleas blooming just before the holidays.
Temperatures averaged about 6 to 9 degrees above normal and precipitation was well below normal in major cities across the Carolinas. That matched predictions by experts this fall. And it may be a sign that we need to shift how we think of 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's La Nina. That's a Pacific weather pattern that pushes the jetstream northward - the opposite of El Nino. La Nina typically causes higher temperatures and drought in the Southeast.
Then, he said,, "We have this general global warming trend that's tending to make things warmer overall, all across the planet," Pershing said. Global warming trends are most pronounced in winter across the United States, he said.
Decembers in Charlotte are 3.1 degrees warmer than they were in 1970, according to Climate Central and National Weather Service Data. (Graph below)
Average temperatures rising
The numbers definitely spiked in December. Charlotte, where the average high temperature in December is 55 degrees, saw 26 days above that. That included a near-record December high of 78 on Dec. 3.
Overall, the city's average temperature for the month - for 24 hours a day - was 53.2 degrees, or 8.5 degrees above normal. That made it the third warmest December since 1878, Pershing said.
Meanwhile, precipitation of just over 2 inches was 40% below normal for Charlotte. Similar conditions have much of the Carolinas now in a moderate to severe drought.
By normal, we mean the average over the most recent 30-year period, from 1991 to 2020. That's how it's defined by experts at the National Oceanic and Atmospheric Administration.
"You look at all of the data from that period, and you characterize temperatures, highs, lows, precipitation, snowfall, all of these things, and it gives you an idea of what climatic conditions you should expect at a location based on that recent history," Pershing explained.
The story was the same in cities throughout the Carolinas. Average temperatures exceeded 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, S.C. (See chart.)
Likewise, rainfall was below average elsewhere, including 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 because of climate change, and that is accentuated whenever La Nina is a factor.
Comparing a monthly average to the past 30 years may be less helpful now because of rapid change over the past 10 years, Pershing said.
"Looking over those last 10 years, all of those years have been above normal, I believe, except for one," Pershing said. "And that's very consistent with this just general trend that we're experiencing. So this idea of a climate normal based on 30-year conditions, and that you can sort of plan on that and have it can have it continue, is really not applicable in some ways in this world with very active climate change."
"Overall we're expecting every year to have a greater chance of being slightly warmer than the prior year," he said.
These deviations from normal make it harder to plan for weather, infrastructure or even your household.
"A big challenge is that a lot of a lot of planning gets done based on the climate normal," Pershing said. "If you're building a road, how big you're going to make the culverts and the storm sewers, that's often determined by the climate normals. How much snow you expect determines the building codes for roofs on 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 people in the climate community are starting to really try to advocate for is to try to use some of these climate projections and build these (building) codes based on the projections, not just on what we've observed," he said. "Because we can easily find ourselves in a case where we've essentially built to a standard that's already passed us by."
Drought continues
Meanwhile, the unusually dry weather and low water levels have prompted officials to declare a Stage Zero drought watch for the Catawba-Wateree river basin, which stretches from western North Carolina to South Carolina.
Stage Zero is the lowest of five drought stages for the river.
The Catawba-Wateree Drought Management Advisory Group says dry conditions are expected to continue, so they're 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 coast was categorized as moderate drought as of Thursday, Jan. 6. That's a slight improvement over the past few weeks.
A version of this story appeared in WFAE's weekly Climate newsletter, emailed every Thursday. Read and subscribe at https://www.wfae.org/sign-up-for-our-newsletters
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