THE DEVIL IS IN THE DETAILS...
This post was intended to be out by Thursday morning but a computer issue caused the delay. Hopefully the problem is fully resolved. Better late than never. Thanks for you patience and understanding. TS
Yesterday I broached the subject of pattern change that I felt was coming in the day 10-12 period. My emphasis was on the potential for an Arctic outbreak and perhaps an increased potential for some snow sometime in a window that extends from January 16-January 23rd. If you missed my rational you can find it here. https://www.tswails.com/single-post/helter-skelter-winter-with-a-snarl
As with any forecast beyond 10 days, there is significant uncertainty and the devil is in the details. Having said that, there was good agreement between the GFS and EURO today on the cold shot around January 19th. The GFS has been emphatic on this for a couple days and shows these departures running around 30 degrees below normal.
The EURO at that range does not show surface temperature departures but it does show them at 850mb (5,000 feet up) where at that level they are nearing 20 below normal...no doubt colder at the surface
If indeed this comes to pass, there is also some evidence that the surge would be initiated by a storm that would impact some part of the Midwest or Ohio Valley about the same time. Whether it's a clipper in the northern branch or a fully phased system remains to be seen as models at this distance have a difficult time resolving energy. Wednesday, the EURO had this.
The GFS had this depicting a bomb exploding over western New York. Today it has little at all, no doubt tied to phasing. I have doubts about the extreme intensity of either disturbance but I still think the door would be open for some nasty cold and wind chills.
So what are the caveats? Probably the biggest issue is phasing. How the energy evolves and merges with the northern and southern streams will dictate the strength of any storm and the intensity of the cold it would pull into the Midwest. These are big issues that are far from being defined. However, the model ensembles and various teleconnections point to some degree of this trend so I'm confident in the big picture that there will be some derivative of this pattern. It could be less severe but I just can't see the route as clearly as I would like due to the distance. The devil is in the details. I will keep you updated but keep this is a good 10 days down the road. Roll weather...TS
