Atlanta cold snap: Why is it sweater weather in the South?

If you woke up in Atlanta this supposed summer morning, you might have walked out on the porch, and gone right back in for a sweater.

On Aug. 16, a time of year when average daytime temperatures hover at 88 degrees in the Phoenix City, the mercury had stalled at 64 degrees at 1 p.m., six degrees below the record low for a high temperature, set in 1892, of 70 degrees.

Thursday’s 73-degree reading was also the coolest Aug. 15 ever on record in Atlanta, besting a record low high of 77 degrees in 1908.

“For what it’s worth, based on our high temperature [on Thursday], there’s some interesting locations that actually got at or warmer than us that were in Canada, Minnesota and Maine,” says Peachtree City, Ga.-based National Weather Service meteorologist Adam Baker.

The news bred localized debates about global climate change, and whether the earth is cooling or warming. One temperature record, of course, can’t be extrapolated into a climatological trend.

In fact, according to the Weather Service’s Mr. Baker, the unusual cold snap is the result of so-called “cold air damming” – in this case, a dome of heavy cold air across New England pushing up, or damming, against the eastern face of the Appalachian Mountains and spilling into the Georgia piedmont along the southern tip of the range.

That blast of chill is then crashing into moist air gliding into the area from the Atlantic and Gulf of Mexico, resulting in heavy cloud cover and a continuous drizzle, creating a bit of an ice chest effect on the ground.

The weather does, however, fit a short-term trend that has seen daytime temperatures in Atlanta, and many parts of the usually sweltering South, remarkably low.

The cause of the cool trend is a jet stream situated unusually far to the South, bringing cooler-than-normal air into the region, which in turn has created a lot of cloud cover and rain – all of which adds up to what many Southerners, especially Yankee transplants, are chalking up as a welcome respite from the usual Dixie dog days.