Monday, November 20, 2016
Two weeks ago I wrote about the upper atmosphere’s attempting to evolve into a different, colder, weather pattern. It tried, as several weak systems attempted to bring in colder air. However, the upper air winds were unable to generate the anticipated west coast ridge- east coast trough. As tv’s Colbert would say, we got some east coast “troughiness”, but not the real thing.
So, two weeks later we find a pattern that still contains a strong upper trough from the Gulf of Alaska southward. New to the scene has been the development of weak troughing over the northeastern U.S. The upper ridge over the southeast U.S. has moved westward and weakened quite a bit. It’s now centered as a very flat ridge over the western Gulf and Texas.
So, what was expected has happened, but to a much smaller degree than anticipated. Now the atmospheric jet stream over North America has been left in an unusual pattern – too little spacing between the two troughs. That sets up an unstable situation which will result in much more weather activity over the next two weeks. We’ll see a big increase in storms and weather changes as energy pockets swing around the big west coast trough, rapidly swing across the U.S. and hook up with the weak east coast trough.
This situation looks to have two possible solutions – 1). The increased atmospheric instability shifts enough energy from the western trough to the eastern trough to allow it to become the dominant system. That results in a colder than normal eastern U.S. for December (and probably most of the winter. Or, 2). The western trough remains dominant and the eastern one never really establishes much strength. That would mean a wet, mild December.
So, which scenario is more likely? Today, both the GFS and European models are favoring scenario number 1. If it works out this way, we could have a very interesting December, weather-wise!
Grey Poupon wasn’t given its name because of the color of the mustard. The moniker actually comes from the names of two 18th century mustard firms from Dijon, run by Maurice Grey and Antoine Poupon.