To be perfectly honest with the folks looking for a lenghty severe cold spell (including myself :-) today's ECM/GFS 500mb height anomalies may just be starting to suggest a change in the upper air pattern, this is in regards to the GFS and ECM starting to show a short cold spell followed by LP breaking through the block, if you look at the GFS mean it does show a more Wsterly flow in 7-10 days time with lower heights filling the void between Northern UK and Southern Greenland, whilst the ECM mean is different to the GFS it would suggest that when these anamolies are at odds with each other a change in upper air pattern is likely, but it needs at least 3 days of continous agreement to suggest the change is likely to happen
Of course the upper air pattern may not change but there is a suggestion withing the 500mb mean that the GFS and ECM op's showing LP breaking through the block may well be right and we could be heading towards a "milder" few days after the cold spell before possibly the block re-builds again??????
I haven't looked at the NAEFS and the above drivel is just based on todays 500mb ECM / GFS anomalies :-)