There have been four years in recent times where the Autumn CET has been more than 0.5C above the 1971-2000 mean in each of the three months. These years are 1978, 2006, 2009 and 2011. It is now a dead cert that 2014 will join this list. So what have the following winters brought in those previous years.
Well it is interesting because in two of the years the winter went on to be very mild (2006 and 2011) whereas in the other two years the following winter was very cold (1978 and 2009). So which way will it swing this year? Who knows but I have been taking a look out of interest to see if we can deduce any trends as regards those earlier years.
I start by considering the daily CET figures for October and November to see whether 2014 shows any pattern with those earlier years. The charts are shown below. 1978 seems the least best fit with 2006 probably the best fit. If we just look at November then 2006, 2009 and 2011 are all quite similar to this year. One very noticeable point is that after a warm end to October there was a sharp (albeit temporary) dip in temperatures in early November. We saw exactly the same thing this year.
So lets compare some key variables for the four years mentioned above. They are summarised in the table below. I have highlighted in yellow those variables that show a high degree of similarity with 2014.
I immediately discard 1978 on the grounds that the NAO and AO indices have shown little similarly in October and November to what we have seen this year. As I mentioned in my analysis in the winter thread the other day the ENSO index seems not to be of great importance as we get cold and mild winters at all phases of the index. The only other parameter that is similar to 2014 is the OPI.
2011 also shows a very similar NAO and AO pattern to 1978 in the Autumn period which is very different to this year. The OPI was positive that year and Autumn rainfall was very low. These factors more than offset the negative QBO that year. So 2011 also seems a poor analogue.
That leaves us with 2006 and 2009. Both these years look interesting. The NAO and AO indices for October and November are broadly the same in each year and very similar to how 2014 is shaping up. Both years were wet in October and November although 2006 will almost certainly be much closer to 2014. The Autumn CET was closer to 2014 in 2006 as well although if you just consider October and November the gap narrows considerably.
Both 2006 and 2009 saw very low sunspot numbers due to the solar minimum. We have greater activity this year but that does not preclude cold weather (again see my post in the winter thread). 1978 is a good example of this. As noted above I don't give much weight to the ENSO as a predictor. The main differences between 2006 and 2009 are in the first two columns of the table.
The OPI was heavily negative in 2009 but positive in 2006. This year the OPI is heavily negative below -2. What you can see from the table below is that in the four years under review the OPI was an excellent predictor of the winter AO. If this trend holds then we can expect a very negative AO this winter. The QBO was also negative in 2009 but slightly positive in 2006.
So my takeaway on this is that 2009 seems to be the best analogue year when we consider how 2014 is shaping up. I am not saying we will see a winter similar to 2009/10 but there are strong similarities with this year.
I have also looked at the NAO and AO indices for all five years for October to December. What this shows is the 1978 is again a bit of an outlier which again reinforces my discarding above of this year as a good analogue. 2011 is also not a great analogue particularly on the AO index. But 2006 and 2009 both show similar patterns up to the end of November as 2014. For the 2014 data I have taken the actual NAO and AO figures to 14 Nov and then used the 10 day GFS predictions.
What we can see is that in the two cold winters (2009 and 1978) the NAO and AO diverge from the other two years as we change month from November to December. 1978 does bounce back briefly but then turns cold again. So for those saying the current model output suggests another very mild winter is almost certain at this point this is way too premature. If we are going to see a pattern change in early December we might start to see significant signs of this in the models in about a week's time.
2006 and 2009 both had fairly neutral AO and NAO figures in the latter part of November. For 2014 the NAO and AO are both currently negative but look like returning to neutral or positive over the coming days. We need to watch for signs of whether they turn negative again as we move into December. If so then maybe we might follow the 2009 path.
There are of course many other possible scenarios when you look more widely at the analogues. One of these is that we see a cold January to March and December is fairly benign. The one thing I am fairly confident of is that we are unlikely to see an average winter. All the signs points to something fairly extreme one way or the other with the probabilities currently favouring a cold winter in my view.