Yes, the pattern change is coming, but not this week. The cold air that will come tomorrow and Wed, will be transient. There is chance of some snow showers tomorrow night as a weak disturbance moves through the area. But that should be it. It will turn much milder again later this week.
It looks like the longwave trof will that will come trough this area on the 15th will persist into the following weekend across the Central and Eastern US, according to the latest NCEP Ensemble Mean (http://www.cdc.noaa.gov/map/images/ens/ens.html) We will also have a +PNA. So this does appear to be a true pattern change. It may get very cold around from 1/17 – 1/20, with high temps 5 to 10 degrees below normal. By 1/21 temps may begin to moderate, but temps will only be closer to normal. Another reinforcing shot of cold air is likely come the following week.
The latest GFS and ECWMF show a couple of waves of low pressure moving up along the artic frontal boundary that will move slowly offshore during the middle of next week. We will see what future runs show.
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Miguel Pierre Weather 