|This Dec. 2011 NASA satellite image shows the cooler than normal sea surface temperatures (blue) that represent La Nina. Credit: NASA JPL|
What is La Nina? It's below-average sea surface temperatures (SST) across the eastern and central equatorial Pacific Ocean that affect (and bend) the path of the jet stream. The Jet Stream is a fast moving ribbon or "street" of air in the upper troposphere that moves from west to east, and storms track along it. The Jet Stream is buldging north of the Mid-Atlantic, keeping that area and the states south of it, warmer than normal.
In a forecast issued on January 5, 2012, NOAA said "During January - March 2012, there is an increased chance of above-average temperatures across the south-central and southeastern U.S., and below-average temperatures over the western and the northwest-central U.S. Also, above-average precipitation is favored across most of the northern tier of states and in the Ohio and Tennessee Valleys, and drier-than-average conditions are more likely across the southern tier of the U.S. (see 3-month seasonal outlook released on 15 December 2011)."
FOR THE FULL REPORT FROM NOAA: http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.pdf