First off, I think two things happened in December that caused the warm weather we have had. For one, the pattern was "reloading" after the very cold November we had. Secondly, a global wind pattern at the equator called the QBO was too strong causing the pacific jet stream become too powerful and prevent the polar jet from sinking south and giving our region cold air. It actually acted like what we normally would see in a strong el nino winter, similar to the image below.
I do not want to bore everyone with the details behind the QBO but basically there is evidence that it will weaken over the next few weeks. This should mean that the pacific jet relaxes a little. A weakening QBO actually supports an active winter pattern in the east in its current phase, so that is clue number 1. Remember a Pacific jet stream is a good ingredient for snowstorms but it cannot be too powerful or otherwise it acts like a blowtorch.
So lets look at November real quick in terms of temps..
No secret it was very cold compared to averages. Without getting too complicated here, the weather pattern had to reload for December. Its is not too common to have back to back months with temps this cold compared to averages.
So how do I know the pattern is starting to reload? The stratosphere and the polar vortex. The stratosphere is now under the process of warming and that warming is projected to split the polar vortex. This is a key component as it will introduce polar air into the country over this next week. The image below shows one level of the stratosphere. Notice the two different cold pools over Canada on the left of the image and over Europe on the right. The warm colors represent the warming that is putting stress on the polar vortex causing it to split into two.
Focusing on North America, we can see over the next week the influence on temps that vortex will bring. Image below is valid for Thursday and shows temps at 5k feet compared to averages. We will all notice a big change in temps this week and it will finally feel like winter.
Here is another view of the vortex over eastern Canada in blue and green funneling the cold air into the United States..
Here are where things CAN get interesting. Take a look above at the green circle over the southwest. That represents a storm system in the southern jet stream. Models project that storm system will travel towards the east coast by late next weekend. The big question now becomes will the storm cut into the interior and cause our area to be hit by rain, or will it slide just off the mid-Atlantic coast and give us the opportunity for snow. The answer to that question is going to lie with how this vortex sets up over Canada and how much cold air presses ahead of the storm. If this vortex presses further to the south and east of Canada like the European model is showing, it will set up a favorable position for high pressure to form. This high pressure will prevent the storm from moving into the lakes and instead cause it to slide off shore.It will also keep the cold air in place over our area. Here is the European model's projection of that..
All areas from Philadelphia north would have a shot at accumulating snow late this weekend into early next week with this set up. The GFS model is not as optimistic as it does not have as much of a ridge in the west and does not press the cold air as much as the European. Regardless, given the fact we are a week away both options are realistic at this point. We are going to have a fine balance between arctic air to the north and warm air to the south. Depending how how the arctic air presses will determine if the snow falls in western NY state or in the big cities.
I will keep everyone updated on this threat this week as things evolve. Based on this pattern change coming I think that vortex will be strong enough to keep the storm out of the lakes and give our area a shot at snow. As long as the vortex does not become too suppressive and cause the storm to move out to sea. If this situation continues to trend favorable I will cut a few videos to explain the set up in better detail. Thanks for checking in, enjoy the colder temps this week!