Torch! Torch! Torch! The weather pattern since November 8th has been very warm in Connecticut. At Bradley Airport (BDL), where official records are kept, the average temperature this month has been 46.8º or 3.2º above normal. Since November 8th the temperature has averaged nearly 6.6º above normal. The biggest reason for this has been a strong Pacific Jet Stream that has flooded the continent with warm air. On the right you can see how the atmosphere looks at 500 mb. The orange/red shades are unusually high heights (higher heights means a warmer airmass) with the blue/purple shades meaning unusually low heights or a cold airmass. A strong pacific jet is an example of a +EPO (Eastern Pacific Oscillation). There are some indications that this will break down in the next week or so which will have major implications on our weather.
On the left is a look at 1, 4, 7, 10, and 13 day forecasts of the EPO since July 25th. The current (and forecast) times are on the right with July 25th on your left. Notice how high on the bar graph the EPO readings have been lately. The bottom graph extends 13 days into the future (first week of December) and shows that the +EPO becomes a -EPO which will reverse the current pattern.
Instead of cold weather over Alaska, British Columbia, and the Pacific Northwest warm weather will be found there with colder weather east of the Rockies.
Another way to look at how the pattern will change is to look at an 8-10 day forecast from 2 of our computer models the GFS and ECMWF. Both computer models really change the Pacific weather pattern quite a bit. Instead of the low heights (blues) over Alaska and the Gulf of Alaska they’re shifted west toward the Aleutians or even eastern Russia. This has a huge difference in our weather and as you can see the high heights in the east have been replaced by low heights (colder weather). Obviously there are some differences in the details (it is 8-10 days out, afterall!) but there is general agreement that the warm weather of the last 2 weeks is going to be leaving and a more seasonal weather pattern is on the way.
So how cold are we talking here? Well, not that cold! For several reasons I’m not expecting a surge of true Arctic air to move toward southern New England. For one there is a tremendous lack of snow cover across Canada which will modify a colder airmass that tries to move south. The other issue here is that even the model on the right (the GFS) which is a colder than average pattern the real cold from the North Pole appears to want to head toward western Europe (UK, France, etc) and not down toward the east coast. Given how warm Canada is currently and the lack of a solid snow pack even up to southern Hudson Bay I have a feeling it’s going to be hard to get truly Arctic air to Connecticut.
Either way the pattern is changing. The Pacific has gone from torch to freezer and that is definitely a good thing for winter lovers. If I had to guess right now I say the first week of December (December 1st-7th) Averages -1ºF (or 1 degree below normal) at BDL.