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Autumn 2020 UK weather

Forecast pointers


03/07/2020

Autumn outlook

Before looking ahead it is worth quickly reviewing the weather so far this year as well as Autumn 2019.

2020 to date

Central England Temperature (CET) has been close to or above the average in all months so far this year. Rainfall levels have been more varied.

Month CET Anomaly
January 6.4 2.6
February 6.3 2.5 
March 6.7 1.0 
April 10.4 2.5 
May 12.5 1.3 
June 15.3 1.2 

Autumn 2019

The season was 0.3C colder than average with a UK mean temperature of 9.1C. This contrasted with the previous autumn which was about 0.3C warmer than the 1981-2000 average. 

The monthly temperatures anomalies were:

September: -0.5C
October: -0.5C
November: 0.9C

Rainfall totals were 110% of the 1981-2010 average.

Sunshine totals were 102% of the 1981-2010 average.

In recent years there has been a tendency for months to be above rather than below CET. That is a significant consideration when looking ahead to Autumn 2020. 

 

Frosty autumn scene

Autumn seasonal model overview

The table below summarises output from seasonal forecast models for September, October and November 2020. It  represents the data available at time of publication and subsequent updates may favour a different outcome. 

Model Temperature Precipitation
UK Met Office GloSea (UK) Near normal Weak bias towards below average
Meteo France (France) Mostly above average Below average in the north west
DWD (Germany) Below average Close to average
International Research Institute (IRI)  No anomaly No anomaly
Jamstec (Japan) Below average Below average in the south, above in the north
C3S multi system (European combi) Above average in the south Close to average
CFS v2 (USA) Close to average Above average

C3S multi system incorporates date from ECMWF, UK Met Office, Meteo France, CMCC, DWD and NCEP.

There is not a clear signal for temperatures. Unusually, the precipitation outlook seems to be better defined with drier than average conditions favoured.

The relationship between autumn and winter has been discussed before. There are suggestions of a correlation between warm autumns and mild winters. 

Background signals

In addition to the seasonal models a number of key points are worth considering:

1) There is considered to be roughly equal chances of La Nina or ENSO neutral conditions during the autumn and winter. La Nina tends to support drier conditions during the meteorological autumn in Spain and parts of France 

2) A more active than normal hurricane season is forecast by the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center. An active hurricane season possibly increases the chance of high pressure areas forming over Europe as storm systems track northeastwards 

3) Current high levels of global warmth

4) Warmer than average seasons have been common in the UK during recent years

The above pointers do not provide a strong signal for the coming autumn.

Summary

At this stage there isn't a strong temperature signal for the meteorological autumn which spans September, October and November. Computer models are showing a range of outcomes and the background signals do not lead in a particular direction.

There is a weak indication for a drier than usual autumn. This could suggest the possibility of warm conditions early on giving way to an above average risk of frost and fog during the second half of the season. The colder conditions late in the season possibly offset the warmer ones early on. However, that is very speculative and only one possibility. There will be more seasonal computer model runs in the coming weeks and another update will be issued before the autumn forecast is released at the end of August.  

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