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After two rather dismal summers, is 2009 shaping up to be a great summer? – University of Reading

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After two rather dismal summers, is 2009 shaping up to be a great summer?

Release Date 09 July 2009

Analysis by the Walker Institute for Climate System Research and the
>Department of Meteorology
.

Two wet and cloudy summers and now it looks like we might be in for a better summer – we've already seen sweltering temperatures of 30⁰C or more. So, just what is happening to our weather? Scientists from the Walker Institute and Department of Meteorology at the University of Reading shed some light on the subject.

Whether the UK experiences a dry or wet summer depends on the course of low pressure systems which track across the Atlantic. High up in the atmosphere is a ribbon of fast moving air – known as the jet stream. It is the jet stream that steers the weather systems which bring much of our rainfall.

In 2007 the jetstream was further south than normal and it steered rainfall systems straight over the UK. What's more, once those systems reached the UK, they tended to "park", dumping rainfall over us for hour on hour - that was what happened on 20th July 2007 when we had severe flooding over many areas in the Midlands and south of England.

But what controls the position of the jet stream and can scientists predict in winter or spring what the summer is going to be like? It's complicated! The weather and climate of the UK and Europe are affected by what's going on all across the globe. Furthermore the chaotic nature of our weather means that many detailed aspects just cannot be predicted beyond 5 to 10 days. Nonetheless there appears to be some (low) skill in predicting the general conditions a few months in advance (e.g., whether the summer will be warmer or cooler than normal).

The Met Office is forecasting a summer warmer and drier than normal www.metoffice.gov.uk/corporate/pressoffice/summer2009/. It looks like there's an El Niño forming in the tropical Pacific – that is a warming of the oceans over the tropical east Pacific - where as in 2007 and 2008 sea surface temperatures were cooler in the tropical Pacific. We don't fully understand the processes and mechanisms, but the warm tropical Pacific could be pushing this year's summer forecast towards warmer and drier conditions. The link between the tropical Pacific and European weather is weak though and there are many other factors that can affect our summer weather.

Of course UK summers have always varied from year to year and will continue to vary from year to year. Climate change will bring warmer and drier summers to the UK, but there will still be the chance of wetter, duller summers, it's just that they are likely to happen less and less frequently. So very hot summers – like 2003 for example – are likely to be the norm by the 2050s and will seem cool by the end of this century.

ENDS

Looking for comment or analysis?

• Ross Reynolds - weather conditions and stats

• Dr Pete Inness - on current weather/climate change perspective

• Dr Mike Blackburn - world-wide factors contributing to UK weather/climate

• Adrian Champion - Tewksbury flooding/change in risk of flooding with climate change

Scientists from the University of Reading are available to comment please contact Kathy Maskell, Walker Institute communications for more information. Tel: 0118 378 7380, k.maskell@reading.ac.uk or the University of Reading press office on 0118 378 7115/7388

Facts and figures for 2009 so far (as of 7th July):

Our highest temperature in Reading so far this year was on Monday (29th June) at 30.4 degrees C, which is well above the monthly average of 19.3C (thats the 1971-2000 average). However, temperatures up into the 30's are not very unusual in June. Looking back over the last 60 years or so, about 1 year in 10 sees temperatures over 30 degrees at some point in June in Reading. The warmest June day on record in Reading was in 1976 (34.0 degrees) so we're still a few degrees short of that.

The highest temperature anywhere in the UK so far this year was 31.8 degrees at Wisley in Surrey yesterday (30th June). That's a well known hotspot with sandy soil that warms up very fast during the day.

Looking back at the year so far, despite the rather cold winter, with several significant snowfalls in the south of the UK, temperatures have generally been above average. March, April, May and June have all been above average, and with the Met Office forecasting a continuation of the warm weather through the summer, 2009 is currently on target to be a warm year as a whole for the south of England.

The highest temperature ever in Reading was 36.4 degrees in August 2003 - a recent heatwave which many people will still remember. That summer's heatwave was also preceded by a warmer than average spring and early summer. That's not to say that we're predicting another record-breaking heatwave for later on this summer, but the years in which we do experience our highest temperatures in July and August tend to have early summers which are also well above average.

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