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Autumn 2018

Warm and dry?


14/07/2018

Autumn outlook

Before looking ahead it is worth quickly reviewing the weather to date this year as well as Autumn 2017.

2018 to date

Central England Temperature (CET) has been above the average in all months so far this year with the exceptions of February and March. Rainfall levels have been more varied.

Month CET Anomaly
January 5.3 1.5
February  2.9 -0.8 
March  4.9 -0.8 
April  9.8
May  13.2 2.1 
June  16.1 1.9 

Autumn 2017

The season was 0.4C warmer than average with a UK mean temperature of 9.9C, in large part that was due to a relatively warm October. The monthly temperatures anomalies were:

September -0.1C
October +1.8C
November -0.4C

It was generally rather unsettled and sunshine totals were below average.

In recent years there has been a tendency for summer warmth to continue through September and that is a consideration when looking ahead to Autumn 2018. 

 

Autumn scene

"Nebelostfriesland" by Matthias Süßen. Licensed under CC BY-SA 2.5 via Wikimedia Commons.

2018 seasonal model overview

At this stage most seasonal models suggest the meteorological autumn (September, October and November) will be warmer than average. The precipitation signal points towards drier than average conditions.

The UK Met Office (UKMO) GloSea seasonal model update issued on 11th July 2018 shows a tendency for average to above average temperatures over the three month period in all of the UK. The probability given is close to 80% with above average temperatures most likely in the north west. 

The precipitation signal suggests levels are most likely to be average or below average.

Source: UK Met Office

Other seasonal models

The table below summarises output from other seasonal forecast models available at the time of publication. Subsequent updates may favour a different outcome. 

Model Temperature Precipitation
IRI Above average in the north. Below average in the north. Above average in the south
Jamstec Above average in the south. Below average in the north.  Below average, especially in the north.
C3S multi system Above average, especially in the south. No significant anomaly. 
CFS v2 Above average. Below average.

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

In general there are signals for above average temperatures and below average rainfall amounts. The strength of the signal varies from model to model but there is enough consistency to take note. An interesting aside is there have been suggestions of a correlation between warm autumns and mild winters. 

Background signals

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

1) ENSO neutral conditions are expected to give way to El Nino conditions during the autumn (65% forecast confidence, NCEP) 

2) A more active than normal hurricane season is forecast 

3) Current high levels of global warmth

4) Current high levels of warmth in much of Europe

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

The above pointers suggest above average temperatures are likely this autumn. A relatively active hurricane season could lead to high pressure blocking in northwestern Europe which in turn may lead to warm air from southern Europe pushing northwards during September and October.

Summary

A warmer and drier than average autumn is favoured. The temperature prediction is made with a higher level of confidence than the precipitation one.

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