Archives for September 2010

Which long range forecast do you trust?

Paul Hudson | 07:01 UK time, Saturday, 25 September 2010

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When I first began my career in weather forecasting nearly 20 years ago, you had to search long and hard to find forecasts that weren't produced by the Met Office. These days though, it seems every man and his dog are at it.

Whether you find your weather forecast in the newspaper, online, on TV or on radio, it can be confusing to find that these products are often produced by different weather forecasting outfits - sometimes telling a different story.

It can often leave the general public bewildered. Which one will be right? And then of course the very same people who compile the forecast often verify it themselves, with the obvious potential problems that can lead to!

So it's great news that my colleague Roger Harrabin has set up a steering group to find out who we can rely on in long range forecasting, with an independent verification scheme using some of the most trusted names in weather, in association with Leeds University.

It will be interesting to see how many weather companies take up this challenge, when there is clearly a danger of loss of face should certain forecasters prove less reliable than others. But I've been told that those companies who decide to decline the offer to participate will be published - leaving the public to draw their own conclusions should that occur.

The Met Office is often heavily scrutinised by the media, after all it's a household name in weather prediction. It was rightly criticised for the barbeque summer forecast of 2009; and the mild winter forecast of 2009/2010.

But how will other forecast companies perform in the face of similar scrutiny? The results should be fascinating.

Here's Roger Harrabin's article that you can see by clicking here from BBC Radio 4's 'Today' website.

Ocean cooling and natural cycles

Paul Hudson | 21:58 UK time, Thursday, 23 September 2010

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Interesting to see research published yesterday from the University of East Anglia regarding the rapid cooling of the North Atlantic around 1970.

Indeed, between 1968 and 1972, the surface temperature of oceans in the northern hemisphere fell by 0.3C.

This was a particularly interesting period during the last century, when global air temperatures were falling, at a time when the burning of fossil fuels was increasing fast in the rapidly developing parts of the northern hemisphere.

The explanation of the cooling between the mid 1940s and mid 1970s, against a background of longer term warming, has by many scientists been put down to the huge increase in sulphur and pollutant particles in the atmosphere during that time, reflecting sunlight back out in space, and hence causing a net reduction in absorbed planetary heat.

This new research concludes that the cooling, between 1968 and 1972, happened too quickly for that explanation to work.

You can read more about the research in this morning's Guardian by clicking here.

Readers of this blog will know that some scientists, more sceptical about the extent to which man is altering global temperatures, have long believed that the overall drop in global temperatures between the mid 1940's and mid 1970's was at least in part due to a natural cycle in the Pacific Ocean called The Pacific Decadal Oscillation (PDO), which was in a cold phase at the time.

The PDO is detected as warm or cool surface waters in the Pacific Ocean north of 20 N. During a 'warm', or 'positive', phase, the west Pacific becomes cool and part of the eastern ocean warms; during a 'cool' or 'negative' phase, the opposite pattern occurs.

It's sometimes forgotten how important the oceans are in controlling the overall temperature of the planet. After all, 70% of the earth is covered in water.

The heat capacity of land and ocean are very different. Land heats up and cools down quickly; oceans heat up and cool down much more slowly and as such influence global temperatures over much longer time scales.

This new research illustrates a point worth repeating again. Even though most scientists believe man made greenhouse gases will cause global temperatures to rise in future, natural cycles play a crucial part too - and not all natural cycles are understood.

It's only a few months back that we learned that a drop in stratospheric water vapour is thought at least in part to be the reason why global temperatures have not risen as fast as computer models had suggested in the late 1990's.

The PDO is in a cool phase once more; and the Atlantic Decadal Oscillation usually follows several years later. The cool PDO on average lasts 25-30 years. With these natural cycles it is easy to see a situation arising where global temperatures could fall - or at least the forecast rise in global temperatures because of man made greenhouse gases over the next 10-20 years may be held back by some of these natural processes

Recent data shows that global sea surface temperatures have been falling for some months. Is it only a matter of time before global air temperatures follow?

Wild Weather

Paul Hudson | 14:50 UK time, Friday, 17 September 2010

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On Monday, as part of the BBC's Science Week, I'll be presenting a new programme, called 'Wild Weather'.

I've spent the last few months filming across Yorkshire and Lincolnshire looking at the region's varied climate, and meeting people who have been affected by some of our worst extremes.

In the version for BBC Yorkshire, there's some fantastic old black and white footage from the BBC archives, including a memorable Panorama special when Richard Dimbleby broadcast live from Sheffield following the mountain wave storm of February 1962. I take a look back at the famous drought of 1976, the floods of 2000, and bad winters, visiting England's highest Inn at Tan Hill in Swaledale.

In the version for BBC East Yorkshire and Lincolnshire, amongst other things I visit one of Europe's biggest flood relief schemes on the Humber; meet a man who claims he saw part of an ancient submerged forests off Skegness; look back at the devastating East Yorkshire floods of 2007, and talk to the founder of the cloud appreciation society.

Wild Weather is on BBC1 at 7.30 on Monday in Yorkshire and Lincolnshire. If you live elsewhere and would like to see it, it should be on the BBC I-Player shortly afterwards.

If you'd like a taster of Monday evening's program, click here.

The first blast of Autumn

Paul Hudson | 14:46 UK time, Wednesday, 15 September 2010

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The first Autumnal blast of the season is upon us, with recorded wind speeds of around 50mph in more exposed parts of the Yorkshire. Of course this is relatively common at this time of the year.The strongest gusts have been caused by funnelling through local topographical gaps, such as the Aire valley which runs through Leeds.

The strongest winds in Yorkshire are often caused by lee (or mountain) waves. The worst recorded lee wave happened on February 16th 1962. The so called 'Sheffield storm' flattened part of the city.

In the early hours of that morning, an Atlantic depression battered the Northwest of the UK. Across Yorkshire, urban areas such as Barnsley and Rotherham reported similar wind speeds to those recorded today. But shortly before dawn, the mean speed in Sheffield increased suddenly to 70mph - with huge gusts peaking at 96mph - levelling part of the great steel city. It was not just Sheffield that was badly affected. 66,000 trees were blown over in and around the reservoirs of West Yorkshire. Perhaps worst affected were the grounds of Chatsworth house in North Derbyshire - virtually all the trees on the estate were uprooted.

The National Centre for Atmospheric Science at Leeds University have renetly conducted research into the Sheffield storm. It shows that the events of 1962 were not unique, and are likely to happen again. Interestingly, by feeding data into their computer simulation, they also show that, if atmospheric conditions repeat themselves, forecasters would have a good chance of predicting such devastating winds.

You can see more on this new research, and other extreme weather events, with some great archive footage, in my new TV programme called 'Wild Weather' next Monday on BBC Yorkshire. There'll be more details on this later in the week.

A very average British summer - and a new local record

Paul Hudson | 16:46 UK time, Wednesday, 1 September 2010

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It has been an unusually cold end to summer here in Yorkshire. Around dawn on 31st August at RAF Leeming temperatures fell to 2.6C, with a widespread frost on the ground. This is the coldest August night time temperature recorded at Leeming since records began in 1947 - marginally colder than the previous record set in August 2003.

Mean August temperatures at the station were below normal at 14.8C, compared with the average of 15.6C. Rainfall was well below normal at 30.6mm compared with the average of 59.8mm. And Sunshine was also below average, with 142.5 hours, compared with the average which is 160.0 hrs.

As readers of this blog will know, expectations of a long hot summer were heightened by one private weather forecasting company, Positive Weather Solutions, who predicted the possibility of a new UK record temperature. You can read my article on the subject, discussing the various summer forecasts that were issued in the spring by clicking here

As it turns out, despite the media hype which surrounded the forecasted 'barbecue' summer, it has turned out to be a very average summer, with temperatures both locally and nationally no where near record levels.

Leeming's figures show mean summer temperatures (June, July and August) were slightly below average, coming in at 15.1C, compared with the average of 15.4C. Summer in North Yorkshire was a little wetter than average, with 161mm of rain compared with the average of 148mm. And sunshine amounts were normal - 504 hours, compared with the average of 499 hours.

From a UK perspective, provisional figures for summer just to hand also show it has been close to the long term average, see table below.

It would seem that the rule that it is statistically very unlikely that a cold winter is followed by a hot summer has once again been proved to be correct.

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