“It’s not likely,” Cary Mock, associate professor of geography, said. “You can never rule out the chance of a freak event, but there’s a 70 percent chance it will be warmer than normal for the next six weeks or so. If we don’t get to colder weather by the end of February, there’s really no chance.”
The fact that the U.S. is undergoing a La Niña event doesn’t help Columbia’s chances of wintry weather.
“Typically, the Southeast tends to have drier and warmer conditions during a La Niña year,” said Leonard Vaughan, a meteorologist at the National Weather Service. “That’s been the case this year.”
La Niña events are characterized by surface temperatures in the eastern Pacific Ocean that are colder than normal.
“This reduces evaporation and often results in a shift of the polar jet stream farther north,” professor and Geography Department Chair Greg Carbone said. “With the poleward shift in the jet stream, cold, Arctic air has less chance of penetrating across North America.”
Also contributing to the recent warm weather is the North Atlantic Oscillation, a fluctuation in atmospheric pressure which influences winds and storm tracks. When the oscillation is in what Vaughan calls “negative mode,” cold air from Canada moves southward, and the jet stream “dips down,” causing colder weather, which is what happened last winter.
“This year, the North Atlantic Oscillation has been pretty positive, which tends to keep the jet stream from making dips,” Vaughan said. “Last year, the North Atlantic Oscillation every now and then would balance out the weather you’d expect from a La Niña, but this year it has been very inactive; it hasn’t had much influence on the weather here in South Carolina.”
The past two months have been “unseasonably warm,” according to Vaughan, who reported that both December and January had average temperatures that were significantly higher than usual.
“January was 4.6 degrees above normal, which is fairly significant, and December was 4.8 degrees above normal. That’s pretty mild, but it’s not the warmest start to winter we’ve ever had,” Vaughan said, noting that December 2011 and January 2012 were the 17th warmest Decembers and Januaries since 1887.
This year’s warm winter is in stark contrast with Columbia’s last, with wide gaps between each year’s average highs and lows.
“During last year’s unusually cold winter, Columbia’s average January high and low were 53 and 30.5. The warm January of 2012 had an average high and low of approximately 62 and 37,” Carbone said.
Despite the warm weather, Carbone warns not to rule out a winter weather event completely.
“All you need is one cold outbreak and a little moisture from the Gulf of Mexico for a single snow storm,” Carbone said. “The odds are against us this winter, but we certainly can expect a few days to be cold.”
Carbone said for that to happen, the cold would have to coincide with a low-pressure system coming out of the Gulf or along the East Coast.
A change in the North Atlantic Oscillation could also spur a period of colder weather or a winter weather event.
“We have about a month, and there’s a chance this month for colder weather if the North Atlantic Oscillation goes negative again. It’s forecast to go neutral or negative in the middle of the month, so maybe we’ll get some colder air in a couple of weeks,” Vaughan said. “It looks like it’s going to be fairly mild, but it’s hard to tell. The way the weather’s been and the way the La Niña has been behaving decrease the chance, but it doesn’t mean it won’t happen.”