May as well lay out my general musing for this month here so we can see how it fares:
- Cold opening 5-6 days
- Then generally mild until at least mid-month (CET climbs to at least a little above the 1991-2020 average)
- Return to colder weather as MJO-led forcing encourages westward shifting of high pressure initially over or just east of Scandinavia (CET dragged back down to the long-term average, then a little below).
That last stage is of course the least confident, though not as much so as would usually be the case, thanks to some strong cross-model support for the required MJO activity plus a weakened polar vortex. Most probable causes of the CET ending up well above my estimate are an unexpected stall in MJO progression, or the encroached blocking high happening to orientate in a way that holds temps up across the UK during that final stage.
All these events also greatly raise the chance of a sudden stratospheric warming event happening in 3-6 weeks time, but that's unlikely to have much, if any, bearing on this month's weather patterns hence the CET.