Despite some of the earlier projections about how warm this fall season could be in parts of the Southeast, it has been closer to average to a bit cooler.
So far in November, Tallahassee, Fla. has encountered temperatures both above and below average as recent storm systems have been able to make their way into the South. Tallahassee International Airport recorded lows in the 30s for three nights in a row (Nov. 15-17) with one morning low a degree shy of the freezing mark.
Meanwhile, locations in New England have encountered plenty of cold weather along with some snow. For instance, places like Albany, N.Y. have recorded 9 inches of snow so far this season – 7.4 inches above normal.
Why the recent cooler weather across the eastern U.S.? Let me tell you the story about teleconnections, and chances are good you may have already heard of one (ahem – El Niño).
NOAA refers to teleconnections as “a recurring and persistent, large-scale pattern of pressure and circulation anomalies that spans vast geographical areas.” Let’s use El Niño as an example. The phenomena, in essence, is the abnormal warming of the equatorial Pacific Ocean waters off the South American coast through the weakening of the trade winds. La Niña is the opposite of El Niño – waters become cooler than normal because of stronger trade winds that allow more upwelling. A phase can usually can last for many months.
With an El Niño winter, the Southeast U.S. tends to see more rainfall because of the pattern shift.
But can the cold snap be entirely blamed on El Niño? Not really. There are others. Meet the North Atlantic Oscillation. NOAA defines the index as “based on the surface sea-level pressure difference between the Subtropical (Azores) High and the Subpolar Low.” With a “positive” phase, there is below-normal surface pressure over the far North Atlantic with higher surface pressure over the central North Atlantic. With a “negative” phase, the differences are switched. A specific pattern can last a few weeks.
With the “blocking” pattern of the negative phase, this leaves a good potential for a trough in the jet stream across the eastern United States. This typically leaves the East, and the Southeast if it’s deep enough, in a cooler weather pattern.
As of Thanksgiving, the NAO index was fairly low. Guidance models are keeping it in the negative phase through early December, keeping the likelihood of near- to below-normal temperatures in the area for a bit longer.
And with El Niño setting in, we’ll continue to see the potential for wetter weather with these storm systems passing through the region. For the next six to 10 days, the Climate Prediction Center has the Southeast under increased likelihood of below-average temperatures and above-average rainfall.
Keep those coats and umbrellas nearby over the next few days.