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Autumn 2020 update

Forecast pointers 2


13/08/2020

Autumn outlook

The first look ahead to Autumn 2020 was issued on July 3rd and remains available to read.

This update takes into account more recent updates from seasonal computer models and background signals. The autumn forecast covering September, October and November will be issued at the end of August.  

Red sky in October

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) Above average Weak bias towards above average
Meteo France (France) Mostly no signal Mostly no signal
DWD (Germany) Above average Mostly close to average
International Research Institute (IRI)  No anomaly Above average in the north west
Jamstec (Japan) Above average Below average
C3S multi system (European combi) Above average in the south Above average in the north west
CFS v2 (USA) Above average Below average

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

In the first Autumn update on July 3rd there was no clear signal for temperatures. Since then a number of models have updated to show warmer than average conditions. 

The precipitation outlook is now less well defined. There seems to be a weak signal suggesting a wetter than average season, particularly in the north west.

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 a 60% chance of La Nina developing during the autumn and a 55% chance of it continuing through the 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

On balance the above pointers tend to support above average temperatures during the coming autumn.

Summary

There have been some changes since the first Autumn update issued on July 3rd. The likelihood of above average temperatures over the season as a whole has increased. 

The earlier signs of a drier than usual autumn have now faded. There isn't a strong signal but wetter than average conditions seem more likely in the north west of the UK.

It is important to remember that a wetter than average season does not preclude the chance of long dry periods. The rainfall could be concentrated in shortish and sharp bursts. Likewise the same logic applies to temperatures. A mild season could contain several cold periods within in.

The autumn forecast is released at the end of August.  

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