December 29th, 2008:
If you read our blog on a regular basis, you know we will frequently talk about ENSO ( El Nino and the Southern Oscillation ). If you are a new reader click on the following link for a definition: http://en.wikipedia.org/wiki/El_Ni%C3%B1o-Southern_Oscillation During the past couple of Winters, we have seen both sides of ENSO. The Winter of 2006-07 was characterized by an El Nino pattern, that brought a lot of snow to most of Eastern Colorado. The Winter of 2007-08 was characterized by a La Nina pattern that brought drought conditions and warm temperatures. So far this Winter, we have seen a bit of a mix. November was warm and dry, while December has been chilly with a little bit of snow. Keep in mind, I am talking about areas east of the mountains. The mountains have been a different story. Repeated heavy bouts of snow and wind has developed quite the snowpack for the central and southern mountains. Avalanche danger remains quite high, and this doesn't show any sign of changing soon. Therefore, this early Winter seems to be resembling last Winter in many ways. Well, if logic holds true we should be under the influence of a La Nina right? Let's check out the graphic below and see what it has to say...
Notice the blue shading across the central and eastern Pacific Ocean. Sea surface temperatures are pushing 1.5 degrees C below normal and are continuing to cool. This seems indicative of a weak La Nina and the upper air pattern seems to support it. Check the map below:
The above graphic shows El Nino and La Nina prevailing patterns. I have displayed this graphic many times, as I believe it tells a very good story. The current pattern we are dealing with is one that is supported by a La Nina. Very wet in the Pacfic Northwest, cold and snowy in the Midwest and Northeast, and very dry from the Desert Southwest to Florida. I see no reason for this to change anytime soon, and that means right through the Spring. Since this La Nina isn't as strong as the one last Winter, it may be able to break down more easily than its predecessor. However, this La Nina may continue to strengthen during the Winter, and that is something we will continue to watch. That's not to say we can't see a big storm east of the mountains, but the liklihood of it happening isn't that great. So, if you are looking for big snow, head to the mountains.
Chief Meteorologist Brian Bledsoe