Pattern Change In The Next 7-10 Days?

Lately, we have been looking for a possible pattern change in the next 7-10 days.  One thing that has me hopeful is the MJO. It looks to go into phase 1.

Phase 1 is an excellent phase for the NE/MA if you're looking for cold/snowy weather. You can see the 500mb composite for Phase 1 for December below.

You can see there is troughing near the Aleutians in the NE Pacific. This usually teleconnects to a +PNA. The +PNA is a ridge over the western states. Over the east, there is a trough. You can also see a -NAO, with the block WEST based as it's over Southern Greenland. This pattern is usually good if you're looking for an east coast snowstorm.

We might be looking at a possible storm in the Dec 15-22 period. Whether it's an east coast snowstorm remains to be seen, but if this pattern actually verifies, the possibility increases. 

First Snowstorm Of The 2011/12 Winter Upcoming!

So far, the winter has been brutal. The last major snowstorm to strike was the storm around Halloween. But now, we have another snowstorm baring down on the NE/MA, including the I-95 Corridor.


I will stress this. This won't be a huge storm. The pattern isn't ideal for a big storm. We currently have a -AO/+NAO and a -PNA. Typically this combination isn't going to allow for huge Nor'Easters along the coast, but we should see a plow able snowstorm come Saturday.


Let's look at a few models, shall we?


First up is the 12Z GFS valid at 24 hrs.

It clearly shows a -PNA. The look here is flat to almost troughy. This is due to the vortex in the Gulf of Alaska which helps to pin the PAC Jet underneath it. This jet helps to knock down every attempt at a building ridge in the west, also known as the +PNA. Because the flow is flat, shortwaves will typically trek west to east instead of diving over the ridge. This also leads to a flat flow in the east. Shortwaves will usually then phase into a trough. Because there is no trough, the shortwaves in the northern stream and southern streams stay separate. So we'll have a storm that travels eastward. The progressive nature of the flow will keep the storm weak and moving. There is no negatively tilted trough to allow the surface low to explode. We do have the -AO which allows the colder air to spill southeastward. The surface highs to the north help to keep in a NE flow, as known as CAD. They squash the surface waves south enough so even the coast will stay cold enough especially up near NYC. The NAO is till positive, so that reassures us this won't be a big storm. 


We can see something similar on the 12Z Euro valid at 30 hrs.

With all said, I only do snow maps for the NYC Metro Area. But because I hate doing maps, I am going for a general 3-6 inches across the area.