The overnight EPS has firmly moved away from the idea of dumping the NS into the weakness/troughing we have set up pre-Christmas as for the most part the NS is allowed to progress eastward. That includes the initial dump we were seeing as well as the secondary that was showing up post Christmas. Thus the ridging/higher heights in the east are very much weakened compared to past runs as they are responding to the weaker feature that sets up in the southwest vs. the the much stronger in past runs. This is a good thing as seen below.
Here is yesterdays heights map. Notice the trough is located in the SW and encompasses both the southern stream and the northern stream. This is a strong feature so we are seeing the typical response in the east with strong heights building.
And this is the response we are seeing with the temps through the CONUS from the above map. Notice we have a -EPO that is driving the NS down from the arctic regions but the flow for the most part is into the weakness in the SW. This flow will then pull eastward a bit before it pulls back north into Canada bypassing the eastern US. So we are seeing strong cold anomalies in the west vs. the strong warm anomalies induced by the higher heights in the east. As I have mentioned time and again we do not want to see this play out. This evolution would wreck the pattern where it would take time to recover potentially a good deal of time.
Now the EPS has been back and forth with the long range pattern but despite that it has slowly been moving to the look I have favored for awhile which can be seen below from the overnight run. Notice that we see a much weaker SW feature. We still see the troughing down there but we are not seeing full latitude trough that we were seeing in the previous example. That is because the NS has bypassed that SW feature for the most part as can be evidenced by the NS trough we see set up in the central portions of the US. Now with the weakened SW feature we are still seeing a response of higher heights in the east but they are much weaker as would be expected. Now typically we wouldn't want to see higher heights in the east even those in a weakened state. But in this case and setup we prefer to see some weak height builds especially to our south and east (SE ridging). There are two major reasons for this. For one it helps to bump up the sub-tropical jet in the east putting it in play for us. And two it helps to mitigate the southward push of the northern stream induced by the -EPO and/or -EPO/+PNA ridge. Without those higher heights in the east the NS can quite often dominate the pattern and be suppressive in the east.
Now look at what a difference the above set up has for temps. We are seeing colder temps through the whole of the northern US as the NS drops south and then expends its energy moving eastward instead of dropping south. Now without the weakened higher heights in the east we would more then likely see the flow take on a more southeasterly track through the CONUS which would probably end up suppressive for those of us in the east. I will also mention that I believe the cold being shown is under done at this point. The setup argues for colder anomalies through the northern US but the models quite often times underplay that at range. If in fact the EPS holds onto this general setup we could probably expect to see a deepening of the cold on future runs.
One last thing. I still like the potential for right around Christmas and that hasn't wavered. Short of a major NS dump into the SW I have thought the pattern argues for a system impacting in the east at this time. At this point whether it is white or wet is still in the air. It really will come down to the evolution of any potential system, whether there is any NS involvement, and how cooperative temps are at that point. I will say though that looking at the current setup I do believe that the models are underplaying the cold through that time.
Here is some eye candy (overnight EPS control run) before I go.