We're almost at the point where I produce preliminary analogues for the Autumn 2018. If you do not know what this is, it's when I bring every analogue together, find the years that came up most frequently and then look at the Autumns of those years. I will continue making a few more analogues after I do that if I have enough time and if years that didn't appear in the preliminary analogues appeared more frequently in the analogues following them then they'll be added.
For this blog post, we're going to be looking at Autumns that followed on from positive NAO Junes. June 2018's NAO figure of 1.41 was one of the most positive values on record showing just how ridgey the Azores High was in June 2018 along with how deep the low pressure was over Greenland as shown by the reanalysis below. For the first batch of these analogues, we're looking at Junes that had a mean monthly NAO of at least 0.50. We'll be cutting this down to Junes that had at least 1.00.
The 500mb height anomaly reanalysis of these Autumns looks fairly anticyclonic with not a lot going on. Heights are relatively above average just to the southwest of the UK with average heights to the north and northeast of Scotland. There is a deep trough over Scandinavia but the above average heights are too close to be delivering any real significant cold so looks anticyclonic. However, there lies a lot of month to month variation as you will find in the monthly breakdowns below so this reanalysis doesn't matter all that much. The Autumns all seem very different in the analogue like there's no comparison at all with say 1992 to 2006; 1992 was a cool Autumn and 2006 was the warmest Autumn on record.
The Septembers of these Autumns look cool with the jet stream on a southerly track. There are low heights over Scandinavia/Russia and the middle of the North Atlantic Ocean with above average heights over Greenland. Heights seem average over the UK indicating not much of a signal. Due to the way the heights are aligned though, it looks cool. There are some very warm Septembers in there mind you like 2006, 1999, 1996 but also very cool ones like 1992 or 1986.
The Octobers look anticyclonic and average temperature wise. Looks almost identical to the overall Autumn reanalysis but the above average heights cover the entire country of the British Isles and the trough over Scandinavia is further eastwards into Russia. Again, there's a lot of variation with Octobers here. For instance, 2013, 2006 and 1996 were unsettled and mild Octobers but 2002 and especially 1992 were cool.
The Novembers look very mild and zonal. The chart is a classic setup for mild and unsettled conditions with deep below average heights to the north and above average heights to the south.
A very mixed picture from this batch of analogues but remember that we'll be cutting this analogue down to less years and only include Junes with a mean monthly positive NAO of at least 1.00 because a lot of these Junes had a mean monthly positive NAO between 0.50 and 0.99. June 2018 was more than 1.00 for its positive NAO so you could say that the years we're going to cut out are less important.