On Monday, December 31, 2012 8:22:05 PM UTC, Ilsington wrote:
I do now want to enter into a great discussion, but a significant SSW is now under way and by mid month the stratospheric zonal flow will have reversed. The Arctic vortex will be well and truly split by mid month and the evidence of the flow reversal can be seen in the extended deterministic forecasts. The ensembles also show a steady decline in temperature that reflects the weakening flow and some blocking.

My dear Dawlish,
It is with great trepidation that I reply as do want to get into a great discussion. Of course you are right to question my assumption, but it is based on experience and some research. In my early days I worked on the interaction of the Troposphere and stratosphere. The main research in those day was the upward propagation of energy and the lid imposed by the westerly vortex (Charney/Drazin. If the vortex reverses then energy is no longer reflected in the same way. We were able to simulate SSW by forcing the 100hPa height clearly showing the two layers interacting. It was really interesting to see how a major SSW could reverse the flow to a great depth.
Anyway just some food for thought, hope you receive this with the integrity in which it was sent.