We have previously looked at the Autumns that followed on from warm Junes and hot Summers overall. Today, we're going to be looking at the Autumns that followed on from hot Julys for the sixth analogue of Autumn 2018. Like the hot Summers analogue, we're not only going to be looking at a reanalysis of the Autumns overall, we're also looking at the individual months themselves that followed on from the hot Julys.
The 500mb height anomaly reanalysis for the Autumns overall shows below average heights over the Bay of Biscay into the south of Ireland and the UK. High pressure is in the middle of the North Atlantic but it ridges back into another high over to the east of Europe. This forces the wind direction to come from a southeasterly. It looks very mild and unsettled, akin to October 2005 which had a similar pattern to what this reanalysis shows.
The Septembers of these Autumns look to be on a knife edge between cool and very warm but what's more clear is the unsettled signal. This 500mb height anomaly reanalysis shows low pressure to the southwest of the UK and over much of both countries.
The Octobers of these Autumns look anticyclonic but maybe on the cool side with the wind from a northerly to northeasterly direction. I am surprised to see such a reanalysis given the Octobers in the analogue. For instance, October 2006, 2013 and 1995 were very warm Octobers.
The Novembers of these Autumns show a blocking area of high pressure over Iceland and the east of Europe with below average heights just to the south of both countries forcing the wind to come in from an easterly direction. The source of the air isn't very cold as it originates from southeastern Europe due to the alignment of the high pressure but it wouldn't be particularly mild either. If that high to the east of Europe retreated northwards through November, it would open the floodgates to cold and snowy easterlies.
You can now see why I decided to do a month by month breakdown for this analogue, each month tends to be quite different in these Autumns. The analogue shows an unsettled September with mixed signals for temperature, an anticyclonic but chilly October and a relatively cool, unsettled November. Would make for an interesting Autumn if it verified this way. More analogues to go!