For a last Autumn 2018 analogue before the forecast is released this Tuesday, I thought it'd be fun to look at the Autumns in the same years that were used for the Summer 2018 preliminary analogues. So for example, Summer 1911 featured in the preliminary analogues for Summer 2018 as it cropped up at least 5 times in the Summer analogues. In this, we're looking at Autumn 1911 and all the other Autumns that followed the Summers in the same years that were featured in the Summer 2018 preliminary analogues if that makes sense.
The 500mb height anomaly reanalysis of these Autumns overall shows above average heights just anchored to the west of the UK ridging into Ireland and parts of the UK itself. There is another area of above average heights to the southeast of Europe along with weak above average heights over the Arctic. At the same time, there are well below average heights over Iberia and Greenland. This looks like a complicated setup because usually in Autumn when you have below average heights, especially to this extent, over Greenland and Iceland, it's a sign of a very unsettled pattern. However, due to there being below average heights over Iberia and the Mediterranean Sea, there is some sort of a battle going on between an unsettled and settled pattern. This is evident from the month by month variation.
The 500mb height anomaly reanalysis for September looks very similar to the Autumns overall but there are important differences. First, the above average heights near the UK are much weaker and more centred in the Atlantic. Second, the above average heights over the Arctic are more intense. Third, the below average heights over Iberia and the Mediterranean are weaker but the Greenland below average heights retain their strength. This to me looks like a changeable September with unremarkable temperatures. There would be settled interludes but there would also be unsettled spells. Not a month that really stands out in the grand scheme of things.
The 500mb height anomaly reanalysis for October looks very anticyclonic and settled with above average heights over top of the UK and Ireland, if somewhat to the east. The somewhat to the east alignment of the high is important because it strikes the balance between some wetter weather out west regardless of the above average heights and a southerly airflow. If the high is over top of us, days would be fairly pleasant in terms of temperature but this is time of year when nights become cold with high pressure and as a result, nights would be cool. It just looks like a very quiet month overall.
The 500mb height anomaly reanalysis for November is very different to the above months and the Autumn reanalysis because high pressure is in the middle of the Atlantic going up to the west of Greenland with deep below average heights centred to the east of the UK into Scandinavia and even going down to Iberia. The jet stream is on a north to south track and we're on the cold side. To me, this looks like an unsettled but cold November with a lot of northerly winds. This of course would give the chances of some early snowfalls.
This analogue pretty much is similar to many of the Autumn 2018 analogues we've looked at but November 2018 is somewhat different here with the possibility of a lot of northerly winds in spite of being unsettled. The analogues have pointed towards an unsettled November this season and may even be very wet but mild. However as mentioned, this one is interestingly different. Remember the Autumn 2018 forecast will be released this Tuesday, August 28th.
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