Friday, December 12, 2014

Friday Morning: Evaluating a real potential winter storm set up

Quick post this morning, but I wanted to show you the period I am keeping an eye on. In general the end  December should be very stormy. The first potential I see for an east coast storm is late next weekend. I will explain why below this image.

You often hear me talk about upper air setups being favorable or not favorable for a winter storm. Above is the European model's ensemble projected out to 216 hours. I want to point our a few critical components that it is trying to hint at. Keep in mind these components do not have to be in the perfect position this far out, I am just looking for them to be in roughly the right area knowing the model can potentially correct.

  • Starting from the left we see we have a potential ridge developing out west. The ridge is not in the perfect position in this image but its close enough this far out. A ridge out west causes a trough in the east. We want that trough over the immediate west coast to be a little more offshore as this evolves
  • Moving on you can see we have a nice impulse of southern stream energy due to the split flow in the jet stream. This gives us our fuel for a storm. The ridge out west increases the potential for a colder polar disturbance from the northern jet to potentiall dive down and combine w this southern stream energy.
  • A critical factor to mostly all big east coasts storm is something called a 50/50 low. 50/50 refers to its coordinates. This low is key because it creates something called a confluence zone to its west. In simple terms this favors high pressure to form in eastern canada/new england and the low to its east prevents the high pressure from sliding offshore. Thus, the cold air is locked in place. We did not have this with the last storm hence the big cold high slid off shore.
  • A 50/50 low ususally goes in tandum with a negative NAO which is the last component I pointed out on the image above. A negative NAO is a ridge of high pressure near Greenland. It serves to cause the cold air to pour into the eastern US from the arctic. 
Right now models project a storm develops in the central us and runs into that area of  cold high pressure. Becuase the high pressure blocks the storm it then is projected to redevelop over the eastern USA.This would mean this potential storm would be classified as a Miller B. We are still very far out and this may not happen, but I just wanted to show you guys the ingredients we need for snow closer to the coast. Ingredients that we have not had yet so for this year. Right now late December is our best shot. Lets see how this trends over the next week.

Here is the Canadian models projection for the same time at the surface.

More as the days go by. 

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