Old Man Winter threat 

Posted: 11:27 am Wednesday, December 6th, 2017

By Kirk Mellish

In my past two blog posts I pointed out how I thought this pattern was atypically unstable and forecasts would probably have to be changed every 6-12 hours. That sure has come true and will continue until the jet stream is no longer screaming right above us.

In a nutshell the divergent output of the models is related to how each is handling the speed shape and configuration of the upper level flow and pieces of energy within that flow, how strong they are and whether they stay weak and “strung out” or gather together to form a more potent upper level short-wave that can form a winter storm system of some kind.

The trend has change from a flat weak system to a more potent one.

Here’s what that upper-flow looks like as of this Wednesday AM, the colors are the vorticity or pieces of energy I was talking about:

gfs_namer_000_500_vort_ht

Here’s how the GFS shows it Friday AM:

gfs_namer_048_500_vort_ht

Here’s how the NAM model shows it Friday AM:

nam_namer_048_500_vort_ht

The NAM model is showing a stronger look aloft that carves out an upper level low Friday into Saturday:

nam_namer_066_500_vort_ht

**IF** this is correct, it would initiate cyclogenesis (surface low pressure formation) in the Gulf of Mexico and COULD produce a “Miller-A” type system bringing real snow to many parts of the Southeast. But details are yet to be determined. There are other models that show just a little rain or have snow that is actually SOUTH of Atlanta!

Screen Shot 2017-12-06 at 11.50.49 AMDQYJwgUVoAAL1v0.jpg_large

There are multiple dozens of models to look at that must be synthesized to make a forecast, not just pointing to snow maps. Forecasting is a process and updates will be forthcoming here and on the radio.

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