TBH we need all three working in tandem but there are other factors at play to consider such as solar minimum and tropical storm activity in the Pacific.
Originally Posted by: Solar Cycles
You've set me up nicely SC;
The emerging signs of an amplifying 'Sceuro' high represent the likely response to tropical convection getting its act together and progressing from the Indian Ocean to the Pacific via Indonesia. Current output gets it far enough to start of a sequence of events that could prove significant for changing our fortunes this winter - but only if the convection can go further still and trigger an important feedback cycle.
Essentially, the stronger the convective signal, the more likely the amplification is to be sufficient for the Sceuro High to build into the high latitudes, at which point it will be well placed to do some serious damage to the polar vortex. At this point, IF the convection holds on far enough east in the Pacific, there will be support for that ridge to persist as a blocking feature on the Atlantic/Europe side while also conditioning the Pacific side for further pulses of convection to develop and move east, again adding amplification to the pattern. Both of these things can seriously hammer the vortex.
There are no guarantees, of course. There's still a significant risk that the tropical convection doesn't play ball, in which case the Scuero High will tend to remain a flatter feature that works with a mid-Atlantic trough to bring frequent bouts of (at times exceptionally) mild air in our direction. In other words, a variant on the current and near-future theme. That then leaves us waiting and hoping for either another area of more organised tropical convection pushing east through the Pacific OR for the vortex to simply blow itself out... which would probably take until February.
A typical strong El Nino favours the latter outcome in a big way - but this year's event is not typical and the recent model trends towards a significant convective event moving into and across the Pacific are a reflection of this. You'll notice I've refrained from calling it an MJO event; this is because the convection is actually too spread out to technically qualify as such - but it can have similar impacts. It just means that analysis tools are less certain and in turn the models will have a harder time handling its evolution (and let's face it, they already struggle enough!).
I am in fact cautiously optimistic about our prospects by mid-Jan, having cast December into the 'unlikely' bin a long time ago.
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