Such a great season for Stratosphere enthusiasts, having followed since circa 2008 when I noticed MJO patterns created predictability, then seeing these working in harmony with strat forecasts, really has been a shift in seeing how the SPV and vortex conditioning has moved slowly into the mainstream.
The SSW competition is pretty cool too- lots of guesstimates on there - I went for Jan 17th predicated on the MJO transition and subsequent 25-30 day lead from P3 to a strat forcing event.. However we are in something of a roller coaster season. Composite included for these pointers from daily values late 70s to date, sign posted another Scandi block developing.
Vorticity plots below outline the imminent Scandi - rock in the pond - block manifesting again and subsequent to this a vortex elongation that teases at Greenland height rises.
Sadly the martineau animations are no longer maintained, however having watched several SSWs over time, the Greenland block to me appears to be the one element that can tip an already perturbed vortex over the edge, we have small signs of this at present. In fact the delay in such a feature taking hold would appear to be via some chaos theory dynamics within how the vortex elongates via the W2 Scandi forcing coming to a peak in the next 2-3 days. A filament of the daughter vortex cleaving from the main parent Siberian vortex and creating havoc in the North Atlantic, essentially disrupting potential retrogression of the block.
Re: Scandi Blocks - it is of note that we have not seen such strong features in this locale for a number of years, before finally showing their hand to strong effect last season, the culmination being a notable easterly regime in the UK and a packet of 500hPa air spilling westward from the continent at -43C, thing of beauty to watch and remarkable synoptic.
I think we will all agree we are privileged to be watching events unfold with greater clarity than before thanks to the work of Zac. Here we see the peak of W2 dove tailing with the W1 displacement, then crucially IMO for Xmas week tentative signs of another W2. In my experience W2 appreciates on modelling following being picked out with amplitude gaining.. certainly this is the case on the ECMWF Berlin plots..
So what of the vortex now, a clear displacement and centroid position exisits for the first two thirds of December, with much scatter thereafter..
Given the variety in guesses for SSW technical, from circa Boxing day thru to nearly all dates in Jan, thru to a double event this season, or no event this season. It's going to be an amazing watch..
If a Greenland block manifests of note, then I think my prediction of Jan is bust, if not then it may be in the area... wonder what others think...