It seems that there is now some more clarity on the cold spell, it seems that the most probable type of cold spell is a polar NWerly with brief periods of atlantic moderation.
Figure 1: EPS ensemble types using diurnal vs airmass variation method.
Figure 2: GEFS6Z Clusters from the weatheronline at 228hr
Figure 3: My personal ensemble weighted snow probability using my own methodology on the nature of the lower atmosphere.
Above are some figures to help make my point. There are a lot of 'warm' blocked EPS runs (fig1), and this matches very well with the GEFS and CMC ensembles (see fig 2 as example). From about the 14th we will start to undergo a transition from zonality to more blocked (although its probably more accurate to say 'less zonal') conditions, although in reality this will only serve to change our airmass type from predominately rPm to Pm. The brief bouts of Tm are still expected to continue though, perhaps at a somewhat lesser frequency, essentially all we are doing is making the cold sectors longer and colder, and the warm sectors briefer and less significant.
With this being said the NW is primed for some excellent conditions (in terms of cold and snow), indeed I expect by the end of January parts of the NW including N ireland and SW scotland in particular will see above average snow amounts (though not necessarily below average temperatures when tempered with the milder earlier part of the month) contrasting with the SE which I expect will have less snow than average.
Figure 3 demonstrates this well, it is for 192hr but this specific is largely arbitrary. This distribution of snow probability will become commonplace I suspect, note the areas in purple - you will do very well. And yes there is colour in the SE, because occasionally weather systems will move into cold air and give localised snow perhaps similar to the boxing day Midlands snow event - though please don't take that to mean I am forecasting those sorts of amounts!
A few notes on differences between the GEFS, EPS, and GEMS:
1) As noted in the clusters the GEFS has more significant periods of moderation than the EPS or GEMS. These periods of moderation could vary from full blown mT warm sectors to atlantic waves from iceland and everything in between, though the former I suspect will be relatively rare. Note that the clustors are going for about a 20% chance of a UK based high, and so is the ECMOP, I haven't ruled this out, but I see the support decreasing in general, just as I see the support decreasing for an Easterly based cold spell. I would rather intepret cluster 3 as one of these periods of moderation.
2) Zonality returning is at probability of about 25% for all three suites, though less favoured on the EPS than the other two.
3) GEMS is showing more significant cyclosis than the GEFS (I can't comment on the EPS I don't have that sort of detail), the result is still some sympathy towards an easterly based cold spell, but far less moderation if we have the more likely Pm based cold spell. The result of this is snowier and colder for the NW but perhaps somewhat ironically less snowy for the SE (the periods of moderation also make frontal snow more likely).
To summarise with a scematic for the end of the month, but more especially for approx 15th-22nd period.
Once again apologies for the overly long post.
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)
Total: 8 days with snow/sleet falling.
2022/2023 Snow days (approx 850hpa temp):
18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)
Total: 7 days with snow/sleet falling.
2021/2022 Snow days (approx 850hpa temp):
26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.