1 November 2011

The Truth Behind Long Range Forecasts

Posted by Dan Satterfield

I’m not a fan of long-range forecasts. There are several reasons, not the least of which is their very limited accuracy. The other (main) reason has to do with the fact that people remember the big storms, and not the average weather! That said, if you’re a utility, or trying to plan heating costs for a large building or school system, an accurate long-range forecast can be worth it’s weight in gold. So, with that in mind, the NOAA winter outlook is out and (while it may bust) I think the reasoning behind it is spot on.


We are definitely headed into a La Nina winter and this would argue for much of the country seeing milder than normal weather. Dry and rather warm conditions in the Southern Plains are especially likely during La Nina winters. Ocean/atmospheric phases like El Nino and La Nina are very helpful in making long-range forecasts, but they are only one of a multitude of factors. Many of these are rather poorly understood, but what may be the two biggest for this winter are the La Nina and the North Atlantic Oscillation (NAO).

The NAO is a pressure pattern in the Atlantic that flips from a positive phase to a negative phase frequently. The negative phase in winter tends to bring in cold arctic air to much of the eastern one-third of the country, and if there is arctic air around, snow is usually not far behind. The negative phase was responsible for some of the big snows last winter in the Northeast, including the very rare deep snow on Christmas Day here in North Alabama.

NOAA’s long-range forecast group is combining the La Nina with the recent trend in the NAO to produce the charts in this post, and I think this is the best that science can muster in 2011. Just keep in mind that we are talking averages, and this forecast is likely to be much more valuable to those planning energy costs, and has little to do with how the winter will be remembered by the public! If you are in Oklahoma, it will likely be a mild winter on the whole, but that doesn’t mean you will not see another historic blizzard!