So here's my final prognosis on the coming Winter 2017/18.
Well it looks like we are heading for a cold start to Winter, but how long will that be sustained for? I’ll try to pin the answer down as best I can using the following indicators:
The current state and trend of ENSO, QBO and Solar cycle.
Autumn SLP anomalies
Atlantic SST Profile.
Also will focus on Autumns that have similar synoptic progressions through the second half of Autumn compared to Autumn 2017.
So starting with the years that are similar to 2017 in terms of the ENSO / QBO / Solar cycle combination to this year, we have:
1962, 1974, 1984, 1995, 1996, 2005, 2007
1983 is not a particularly close Solar Cycle match, but does have the best QBO match to 2017, so I will include that year too.
So the composite for these years gives us a cold UK Winter with anomalous High Pressure to the north/NE, and Low Pressure to the south and SW.
Autumn Pressure Anomalies:
October 2017 was a mild and dry month in the UK with a High Pressure anomaly just to our south. From the overall analogue years, 1962, 1984 and 2007 also matched to the October 2017 SLP anomalies. So for me this basically reinforces the idea of a cold, blocked Winter with High Pressure frequently located to the north/NE of us.
I then looked at Autumns that had a similar kind of synoptic evolution during the second half of the Autumn season, and in particular noted Autumns that had a lack of S/SE/E winds in November, and also had a repeating cycle of increasingly frequent and lengthy northwesterly spells associated with an expanding Greenland High. All these features that have occurred in Autumn 2017.
This is where it gets interesting!
I looked at all years since 1960, and found the following five Autumns that were similar in terms of the combination I mentioned:
1969, 1981, 1996, 2005, 2008.
All these Autumns were followed by a cold, if not very cold December, and indeed most of these Decembers had a significant wintry spell, tending to arrive between Christmas and New Year. Dec 1981 is the exception as that was severely cold and wintry for most of the month. 1981, 1996 and 2005 are particularly interesting because they are also ENSO & QBO matches for this year, although are a poorer Solar match.
So it does look like December 2017 will be a cold month, but the question then is, will the cold weather carry on for the rest of Winter? Well looking at the main ENSO/QBO/Solar analogues, that does seem to suggest cold conditions persisting right through the Winter with an anomalous easterly flow into the UK. However, factoring in the synoptic pattern established later this Autumn, (although this usually does favour a cold December, and indeed a cold start to January), the second half of these types of Winters tend to be milder and with no more than fleeting cold spells returning on the odd occasion. And furthermore, factoring in the current warm state of Atlantic SSTs may well add to the Atlantic influence later in the Winter. The fact also that 1981, 1996 and 2005 are the broadest matches in terms of recent synoptic developments and main indices, reinforces this idea even more.
So in summary then, my prognosis for Winter 2017/18 is:
December 2017: A mix of cold and milder spells initially, then a more significant and lengthy wintry spell later in the month, this more likely starting in the period between Christmas Day and the end of the month. A cold month overall, potentially very cold and wintry.
January 2018: A gradual easing of cold/wintry weather, leading to a milder second half, although still with the risk of a cold snap. Could still end up on the cold side overall, but probably close to average.
February 2018: The odd cold spell still possible, but more likely to be rather mild at times with an increasing Atlantic influence.
Winter overall: Rather cold. Wide variations in rainfall likely, but probably leaning towards being slightly below normal for the UK as a whole.
Gainsborough, Lincolnshire.