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Autumn 2017

Current outlook


13/07/2017

Autumn outlook

Before looking ahead it is worth quickly reviewing what the recent weather has been and how Autumn 2016 played out.

2017 to date

Temperatures have been above the average for much of the year to date and most seasonal models suggest the rest of the summer will be quite warm. Rainfall levels have been more varied and the prospects for the rest of July and August are uncertain.

Autumn 2016

The season was 0.3C warmer than average with a UK mean temperature of 9.8C. The monthly temperatures anomalies were:

September +2C
October +0.3C
November -1.3C

It was generally drier than average and sunshine totals were slightly above 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 2017. 

 

Autumn scene

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

2017 seasonal model overview

At this stage most seasonal models suggests the meteorological autumn (September, October and November) will be warmer than average. The precipitation outlook is more nuanced but a weak signal which points towards drier than average conditions could be emerging.

The UK Met Office (UKMO) GloSea seasonal model update issued on 11th July 2017 shows a strong tendency for above average temperatures over the three month period in all of the UK. In the north west the chance given is close to 80% leaving only a 20% chance of average or below average temperatures. 

Other seasonal models such as the JAMSTEC, IRI and CFSv2 are also pointing towards above average temperatures. The June JAMSTEC update indicated colder than average temperatures for September, October and November but the July updated has flipped and it now supports a warmer scenario. The precipitation indications are inconclusive. 



Background signals

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

1) ENSO neutral conditions are favoured through the autumn 

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 more 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 at times during September and October.

Summary

A warmer than average autumn is strongly favoured at the current time. The signal for precipitation is a lot weaker, but on balance the TWO view is that drier than average conditions are slightly more likely over the the three month period.

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