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Kirk Mellish's Weather Commentary

Posted: 6:30 p.m. Wednesday, Oct. 20, 2010

Atlanta and much of the Southeast dry as a bone on Halloween 

By Kirk Mellish

The southeastern United States has endured a serious dry spell for the past several weeks, and with winter approaching, the region may be in it for the long run.

To put matters into perspective, Birmingham, Ala. has recorded just 54 percent of their average rainfall since June 1. Atlanta had only 39% of normal rain in September and so far this month only 3% of normal October rain.

As spring gave way to summer, the Bermuda High, typically positioned over the western Atlantic Ocean during the summer months, was found farther west over the South for much late Summer and early fall. This not only led to the warm summer the region endured, but it also deflected a large amount of precipitation to the north.

The old saying is "drought begets more drought," this is due to what is known in science as a positive feedback loop.

As the temperature rises, evaporation increases, which in turn dries the ground, which then heats the air more. This cycle is a self-intensifying loop, and it set the stage for months of dry conditions to follow in the South.

With the exception of Tropical Depression 5, the South has been spared the majority of the 2010 season's tropical activity. Although hurricanes can be devastating for the Southern states, the area relies heavily on the rain tropical storms bring. This lack of tropical activity has added to the South's drought woes.

Unfortunately for the South, there is no strong likelihood of tropical activity to help the drought situation before the season ends.

However, global computer models are hinting at some good rains and/or severe weather in the Southern states and parts of the Southeast in the weeks ahead.

As hurricane season makes way for wintertime, problems will likely continue as a La Niña pattern winter will move into place over the next several months leading to worsening drought.

During a La Niña winter, the southern jet stream moves northward, taking with it a significant amount of precipitation. The lower half of the country experiences dry, mild conditions throughout the season. So the best hope for beneficial rain is now before the La Niña winter becomes established.

dry as a bone
Photo: accu graphic
La Nina to add to dry spell in winter