Monday, December 15, 2014

Monday Morning: An Updated look at the Ingredients Behind Potential Big Storm Sunday

Good morning, as promised I wanted to give an update on the threat of a winter storm late this upcoming weekend. In my post last week, I mentioned how we needed to keep a close eye on this threat because it was showing hints at the upper air signature required for major storm development. A few days have gone by and those hints are still there and starting to produce a few plausible scenarios for this storm. This is the first time this season that we will have colder air to work with ahead of the storm. This is a big change from all the other storm threats we have received this season. The big question mark now is will the cold air be the saving grace or will it be too strong and sheer the storm out to sea. Let's take a look at the drivers.

The image above is the GFS models projection of energy in the upper atmosphere 48 hours before this potential storm. Lets review the updated ingredients we are working with.

  • A western ridge in the jet stream.
    • this supports a trough to develop down stream and increases the chances that a northern jet stream component will dive down into the flow. A very essential ingredient to an east coast storm
  • Energy on the field!
    • Looking at the two red circles you can see we have disturbances or energy in the jet stream. The circle on the bottom represents the southern branch jet stream energy and the circle to the north is the northern jet stream energy. All big storms usualy phase the two. You can see in this image that they are both heading on the right path. 
    • This is basically a split flow in the jet stream
  • Looking to the top right corner of this image we have a very critical ingredient which is a low pressure system over eastern Canada.
    • This is one of the most important factors in my opinion because it is the key to where the high pressure system ahead of the storm is placed. The reason is its placement over eastern Canada results in something called a confluence zone to its west. In a confluence zone you tend to see high pressure develop at the surface.
    • This high pressure system supply the cold air for the storm! 
    • With out this 50/50 low any high pressure area will be allowed to just slide off short and the cold air leaves
    • You can see I labeled the high pressure system to the 50/50 low's west. The placement of this low stops the cold high from sliding offshore too quickly.
  • Along with a 50/50 low we usually have a negative NAO to go with it. Models are hinting that this could happen as well. 
    • A negative NAO is high pressure over Greenland. This high pressure helps buckle the jet stream south and aids in the supply of cold air. 
So you can see the many factors we look for in a major east coast storm are present. However, its never that easy. Getting a major storm requires all these ingredients to come together perfectly. For example, if that high pressure center is too strong due to the confluence zone being too far south it suppresses the storm out to sea similar to what the Canadian model is showing.

This is certainly a possibility, but I think the Canadian is a little too extreme with this suppressed scenario. 

The european model is more agressive with placing all these ingredients in a more favorable position. The result is a low pressure center that is closer to the coast and results in heavy snow for many areas including near the coast..

Turning to the GFS, it is similar to the european but not as strong with the storm..

So all these models will now start to flip flop with their surface projections of this storm. The important thing that I will be studying is the evolution of those factors way up in the atmosphere which produce the surface outcomes. Right now its a matter of do we get a major storm or do we get a suppressed non-storm scenario. I know I have a bias to want snow but I think this storm occurs. The reason is I think once all the energy is sampled properly by the models, we wills see a more aggressive upper air setup in particular a more stronger northern disturbance than what is modeled.  Regardless, whether this pans out or not we have a lot of potential right behind it for Xmas week. We look to be in for a while ride!

Stay tuned I will keep you guys updated daily on this threat via this blog and twitter. 

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