The White Christmas Dilemma – 12/20/2011 update

Not much has changed since the previous writeup I did before exams kicked in. We still have had a significant lack in the mechanisms that drive cold air into the eastern US and as a result a persistent zonal flow that has locked the coldest air up to the north. That doesn’t mean it can’t snow in the east (there are some late-season examples of that happening), but it becomes less likely because the source of cold air is cut off.

We have an interesting setup coming into the latter part of the week as we approach the Christmas holiday. Everyone loves to have snow around for Christmas, and unlike previous years, this forecast has been quite elusive even to the most skilled forecasters. Here’s a look at how things are shaping up currently:

You can see whats left of the low that brought the blizzard conditions to Oklahoma, Kansas and New Mexico over Missouri moving north and east. That is storm #1 for us here in the northeast that brings rain for us on Monday. The upper level pattern is another thing to note, we have seen this almost continuously from the late fall into the first part of the winter. You can see this on a PVort map as well with the trough phasing over the southwest and the northern stream breaking off as it pushed east. This alone has been disastrous in terms of trying to get a storm into New England. You may be able to see it as the 500MB level but if I show you the jet stream level flow – you’d see this large zonal air stream tearing right along the Canadian border.

The next question is can we get this to phase further east with the next piece of energy swinging into the northwest? If we can get a positive PNA, we might. The NAO isn’t going to help stop the progression of the northern stream, but if the southern stream can get forced east, that would be our hope of getting this to work.

I do know two things:

  1. The GFS is notoriously bad with phasing
  2. The Euro has been much more consistent and does bring develop something toward the end of the weekend.

I am not ready to jump on board the possibility of a snow storm, but If I had to pick a date in which it is most likely to snow it would be Christmas day. Storm #1 is rain tomorrow, Storm #2 is Friday-saturday which will have absolutely no cold air to work with so that’s rain – the snow would hit mainly the Berkshires on north and west.. On the back end of storm #2 comes storm #3  on Christmas day, which if it holds together looks like the most likely scenario. I’ll have a map later this week if this storm becomes more likely.

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