OK a few quick observations regarding the models today. Little change in the position of the upper bearing high, and tbh as time passes, that is to be expected. One thing is clear to me, if nothing else is. The models predicted the position of this major feature very well even well into FI, even if the surface pattern was not quite right. Anyway, the high will become a prominent feature at the surface and upper levels in the beaufort and canada. The spoiler in this case is greenland itself. Usually it wouldn't be too difficult to ridge directly into greenland and increase the heights from WAA in the atlantic. However this doesn't happen so well, mostly because greenland is swamped by cyclonic activity and low heights - actually the pressure is unusually low over greenland. So instead of any direct ridging, we are getting the HP wrapping through the beaufort and Northern canada and trying to get to greenland by pushing towards the baffin. Meanwhile the WAA continues to be strong over the bearing and alaska. The result of this, is, despite a more indirect route, broadly the same I think. Eventually the cyclones will clear from greenland and allow high pressure to quickly build over the island. With virtually no cyclonic activity to speak of in canada, it won't be long until heights are not only rising from the pacific arctic, but also from the atlantic - presumably from a midatlantic ridge, moving west towards canada. Because of this diversion, the transition to cold weather is still looking painfully slow - but despite this I still think it will happen abeilt probably more likely towards the end of the range I originally stipulated. The caveat to this of course, is that when the greenland high eventually does form, the scandi low will already be in place to deliver some rather cold uppers (I say rather cold, because the arctic is unfortunately very warm for the time of year - as is scandanavia itself and most of eurasia).
EDIT: the 18z illustrates very well what I am thinking about
http://cdn.nwstatic.co.uk/gfsimages/gfs.20131124/18/192/npsh500.png
We have the two areas of high pressure, over alaska and the north atlantic. In the middle is a shallow greenland high. Taking this chart literally, northern blocking would happen very quickly with the north atlantic high transfering to greenland. The LP over iceland will follow the jetstram and take a path SE, which will become increasingly more southery as the pattern becomes increasingly less flat.
Originally Posted by: Quantum