Tango

LATE NOVEMBER / EARLY DECEMBER First cold spell? Recent modelling has been suggesting the potential for a very early (record breaking, in fact) major sudden stratospheric warming, this is when the usual westerly circulation above the Arctic reverses to easterly, whilst the likelihood of this remains uncertain, there are other key global drivers beginning to emerge. During early November the MJO is now forecast to emerge into the east Indian Ocean and begin progressing eastwards through the Maritimes and into the Pacific as November progresses, this will trigger a renewed rise in AAM tendency (within an already very high AAM base state, thanks El Nino!), given the lag times involved with any potential SSW downwelling, the MJO triggered rising AAM and progressing into the Pacific, you could perhaps make a reasonable prediction that the later part of November / early December would increasingly be favourable to amplification of high pressure and high latitude blocking episodes. i.e, is this perhaps the first signal of an early cold spell beginning to materialise? A few weeks ago you'd have been pretty bold to call anything other than a +NAO, Atlantic dominated pattern through November & December, the tide does appear to be changing on that idea. Regardless of any SSW, the possibility of a coherent MJO cycle + rising AAM would have been shifting the thinking anyway, an early SSW probably wont hurt in helping that idea along.. SUMMARY: The likelihood of blocking / colder outbreaks late November into early December appears to be growing some traction on the back of latest developments. Whilst a milder, unsettled & stormier outlook had been anticipated for that period initially, new developments are starting to suggest other possibilities.