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Autumn 2009 started on a mild note and many of us may have been thinking that winter might just let us off the hook.

However, with winter officially starting in less than a week's time we are looking at the weather turning wintry too.

Throughout October and November the UK was under the influence of warm air with subtropical origins, this kept temperatures above average and brought notable amounts of rainfall.

In contrast and since the weekend we've seen a shift in the source of our air; from a warm southern ocean to a cold eastern continent.

Thanks to the dominance of high pressure we'll be bringing in air that's travelled from the bitter plains of Russia, delivering a biting wind and temperatures that struggle to get above freezing.

So it's going to be cold, is it going to feel cold?

How we interpret temperatures varies according to a number of factors, chiefly the humidity of the air and strength of the wind. These combine to produce a phenomenon widely termed "wind chill" and provide a scale by which we can measure what the temperature "feels like".

The brisk and dry easterly wind this week will make the temperatures feel quite different. For example an east coast day time maximum of 2C may actually feel like -2C once the wind chill effect has been accounted for.

When these values are significant we'll be doing our best to highlight them in our broadcasts so keep your eyes peeled.

Meteorologists often talk about broad areas of air with common characteristics.

Air masses as they are collectively known move large regions of air with similar temperatures and humidities about the globe. They receive their attributes according to whether they form over warm or cold land or oceans.

We've been working on a way to illustrate this technical piece of data as a clear and representative graphic. We think this new graphic does a good job of showing why it's going to get colder or warmer because it shows where our air is coming from.

By showing the movement of the mass of cold air, represented by shades of blue, we can describe one of the mechanisms influencing temperature and get an insight into the incredible forces at work within the atmosphere (we'll be trialling this on Weatherview over the coming weeks).

And it doesn't stop there, the movement of the blue colours also reveals another property of the cold air; its potential to produce snow.

So what about the white stuff? Well some areas are certainly in for a light covering over the next few days but the regional details are particularly important; many western parts of the country are likely to be wondering what all the fuss is about.

To keep abreast of the latest forecast for your region the provides local video forecasts as well as a detailed five day outlook.

If you're interested in anything a little further away (a white Christmas or wet New Year maybe?) the gives our best guess of the next four weeks and how conditions are likely to vary.

We hope the additions to our winter forecasting armoury will give you a better idea of why the weather is varying and also help to keep you better prepared.

Of course, you'll still need to look out for the specific details of rain, wind, frost, fog and temperature, all of which can combine to provide hazardous winter conditions.

Jumpers at the ready.

Richard Chapman is editorial manager of .

Since the launch of the new-look weather site back in February, we have continued to develop it, and we have moved content from the old site.

Most recently, we added the Monthly Outlook to our . We've also made improvements behind the scenes to make the site quicker to load and even more reliable.

The next release of improvements, coming soon, will be visibly more noticeable than others we've made since February.

These are part of our continuing effort to make the site clearer and easier to use, whether you use the site to get a quick snapshot of the current forecast or want more detailed information about the weather conditions.

Following feedback from our audiences, and ideas from our weather team, we have made it easier to "Find a Forecast" when you arrive and easier to scan the 24-hour and five-day forecasts to see the weather trend over the coming hours or days.

Everything you found on the site before, you'll still find there now - it'll just be easier to get to the forecast information you need.

When you arrive, you will see our Forecast Finder has more prominence and a new UK Summary gives a quick snapshot of the weather across the UK. The full set of UK maps is still available on the UK Forecast page.

Once you've found your local forecast, you will see that the 24-hour and five-day information is arranged on two tabs again. We have put back the temperature and wind symbols rather than displaying them as text. You can also choose to view all the available detail we have for each of the five days.

As I said above, these improvements are building on the work we started in February and we'll continue to add further improvements and new features in the coming weeks and months.

Richard Chapman is editorial manager of .

With low pressure remaining the dominant force of our weather this week and the heat-wave of late June now seeming a distant memory, the question many people are asking is where has the summer gone?

The latest Monthly Outlook from ÃÛÑ¿´«Ã½ Weather shows increasing confidence that by the end of July and into early August we will see a return to warmer and more settled summer weather.

It is expected that the Azores high will build northwards and become more dominant. This will result in above-average levels of sunshine for the time of year and a rise in temperatures.

There is still a possibility of some further rainfall at times but it should be much drier than of late.

So why have we moved into a spell of unsettled weather with heavy showers, many of which have been thundery and accompanied by gusty, squally winds? The answer is the "jet stream".

The jet stream plays a fundamental role in our weather and its position can cause significant variations in our weather.

Over the last few days the ÃÛÑ¿´«Ã½ Weather team have been using the jet stream graphic to explain how this is affecting our current weather pattern.

ÃÛÑ¿´«Ã½ broadcast meteorologist John Hammond says:

"The jet stream graphic introduces a broader meteorological context to the 'poor' weather we are experiencing.
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The viewer is given a clear, shorthand explanation of why our summer has 'deserted us'. In essence because the jet is unusually far south its attendant wet and windy low pressure systems are being dragged across the UK.
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Normally they should be much further north at this time of year, allowing high pressure to settle the weather down.
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Until the jet migrates northwards again, high pressure and warm sunshine will be rare and fleeting."

You can find out more about how jet streams were first identified and what they are here on the ÃÛÑ¿´«Ã½ Weather site.

During the last week the jet stream has taken a more southerly track across the Atlantic than is normal for this time of year. As a result, we are seeing a conveyor belt of low pressure systems making their way across the UK. Each of these has brought an intensification of showery activity and windy conditions with sunny spells in between. In the short term this looks likely to continue.

Like many of the additional graphics we use to help tell the weather story, such as the Atlantic pressure chart, the jet stream will not be used every day. However, when it helps tell the weather story and explains why we are experiencing one weather type or another then you are likely to see it used on our television broadcasts.

Without wishing to fall into cliche mode February 2009 will always be remembered by the team as a month of two halves.

According to provisional Met Office figures, as a whole, this winter is expected to be the coldest in the UK since 1995/6. The low temperatures have also been accompanied at times by heavy snow.

Monday 2 February saw heavy overnight snowfall in south-east England, the heaviest snow in 18 years, causing trains and buses to be cancelled, and airports and schools to be closed.

Some parts of London saw up to 20cm (eight inches) of snow with the highest accumulations reported on the North Downs at 28cm (11 inches).

There was little comedy value for those of us who needed to get to work but with hundreds of schools closed many children enjoyed making snowmen as the thousands of .

The snowfall also raised the question of imperial units versus metric measurements. Our weather policy has not changed over the years and we continued to present the data in metric with conversions, in this case to inches, when significant.

Although, I have to say at times it did remind me of one of the most famous lines in comedy, from Hancock's Half Hour, The Blood Donor: "A pint, that's very nearly an armful," as we did our best to present the detail of the snow depths and offer conversions when the pictures really told the story well enough.

Aviemore recorded the lowest February temperature since 1986 (-18C) on the morning of the 9 February, Altnaharra in the Highlands was down to -15C and Aberdeen was -12C.

From the 15 February the weather turned much milder and we entered a far quieter period of weather. Temperatures peaked at 15.3C (59F) in Charlwood, Surrey on Friday 27 February, making it the warmest day of the year so far.

Of course, the weather itself was not the only major feature of February 2009 for the ÃÛÑ¿´«Ã½ Weather team. As you may have noticed from my previous blogs on the subject we managed to plan the launch of our new look weather website just in time for the significant snowfall.

Although this produced major interest in the new site it also presented us with a problem. The traffic to the site was greater than we had ever experienced with a reported 500,000 users per hour. As a result the decision was taken to roll back to the old weather site until we were able to ensure we could cope with the increased traffic numbers.

It took a huge effort by the project team to ensure that we had the resilience to migrate everyone across to the new look site and during the last week in February users of the weather site were re-directed to the new version.

Some pages still need to be migrated over to the new design and this will happen over the next few months. So take a look around the new site and let us know what you think.

And for the outlook, the first week of March is seeing temperatures dipping back down below the seasonal average, as cold air floods across the UK. And with that comes a return to wintry weather.

As I commented on this blog yesterday, like many other commuters I too have had to endure this week's . While we can't improve the British weather, we have now done everything we can to improve your ÃÛÑ¿´«Ã½ weather website.

ÃÛÑ¿´«Ã½ Weather has always used developments in technology to improve the quality of its output, dovetailing improvements in forecasting techniques with new and emerging broadcast platforms.

On my first day at the ÃÛÑ¿´«Ã½ Weather Centre the output was focused mainly on forecasts on television. Today the Weather Centre is a fully multi-media operation with over 100 broadcasts a day, presented by a weather team of 22, on TV, radio, online and the red button.

It wasn't until 1998 that the first version of the weather website went live, and it was a very different looking site from the version that is available from today. We have had a couple of site refreshes over the last decade but nothing on the scale of today's offering.

Firstly, we have made changes to the technology driving the website which will mean that we can support the service far more effectively, 24 hours a day. Technology has developed to such an extent that what was thought cutting edge five years ago is in fact old technology today. We have improved the infrastructure and streamlined our processes, which will mean more and faster updates throughout the day.

Secondly, we have been asking you what you would like, and having reviewed that feedback, we have been able to provide what we believe to be a world class weather website. Through the site we will deliver the latest and most comprehensive forecast available for wherever you want, whenever you want it, all in one place.

So I guess you are asking what has changed?

The two biggest changes are the structure of the site and the visual design. All of our forecast information is now organised by location rather than by type of data. Once you have searched for your location you will find everything you need on one page, a one-stop shop for wherever you choose to be. The visual design now follows the broadcast design, so the colour of the pages reflects the weather forecast for the location you are looking at.

Today's forecasts for UK locations on the weather site are no longer depicted by one summary symbol. Today is now covered by a three-hourly breakdown to show more clearly how the weather will change over the 24 hours to come. We have also increased the frequency with which we receive forecasts from the Met Office.

Each location page displays the accompanying weather map, but you can also navigate to other map areas without leaving your page. This means you can choose a different or wider area map if you prefer.

Our forecast information is displayed in individual modules on a page, and these can be expanded or collapsed depending on whether you are interested in the information or not. We are also making the video we produce more accessible by embedding it on our pages, still presented by your familiar ÃÛÑ¿´«Ã½ broadcast meteorologists and updated throughout the day.

Our website is now wider. The ÃÛÑ¿´«Ã½ has received feedback from you about making the best use of available screen space. We're confident that now is the right time to use the extra space to improve the site. The flatter structure of the site will make it easier to navigate.

The process will be completed over the coming months as we migrate a number of pages from the old site to the new. We will also be looking at how we can develop new ways of getting our weather content online and available whenever you want it.

UPDATE 1415: Earlier today we launched the new ÃÛÑ¿´«Ã½ Weather website. Unfortunately shortly after midday we experienced major technical issues. As a result we've had to roll back to the old weather site.

We are urgently trying to understand what happened and hope to be in a position to clarify the situation later today.

The old version of the site will continue to be updated as normal so you can still access the very latest forecast from the ÃÛÑ¿´«Ã½ Weather team. Apologies if you've come to view the new site, but we are doing our best to resolve the issues and hope to unveil the new site shortly.

Richard Chapman is editorial manager of ÃÛÑ¿´«Ã½ Weather.

Like many commuters I spent the first part of Monday morning standing at the station despite the warnings, believing that a miracle might happen and my train might still arrive to take me on the daily trip to London.

Watching the weather output and talking to colleagues who made it into the office, it was clear that we were experiencing an unusual event. Despite the statements that it was the worst snowfall in south-east England for 18 years, it was not until this morning that I realised the magnitude of snow that had fallen.

On my journey from the Kent coast the amount of snow lying just increased and got deeper up until the point where the tracks were not visible on the lines that had not been cleared.

Yesterday many comparisons were made with other European countries, who despite their prolonged winters and heavy snowfall continue to run their public transport and go to work. I assume that if we too experienced these extreme conditions regularly they would become the "norm" and we would cope far better.

The forecasts from the ÃÛÑ¿´«Ã½ Weather Centre at the end of last week contained early mentions of the potential for snowfall this week. Special graphics were commissioned as "attention getters" to make sure that the potential for snow was presented clearly. As the forecast became more certain across the weekend, the graphics were used extensively as the extent of the snowfall became evident.

The Weather Centre today is a hive of activity, with everyone feeling the effects of the busy day yesterday. Ice is still a potential problem in many areas as snow melts during the day and freezes overnight (temperatures in some rural areas fell to -8C last night).

On top of this we are watching the forecast closely. I spoke to Matt Taylor, ÃÛÑ¿´«Ã½ broadcast meteorologist, earlier about the outlook. He said that the wintry weather would last until the weekend and some parts of the country would see further snowfall leading to disruption.

It is definitely worth keeping in touch with the forecast on television, radio and online, as we have clearly not seen the end to this particular spell of cold weather yet.

Richard Chapman is editorial manager of ÃÛÑ¿´«Ã½ Weather.

Whilst I cannot predict a change in the balance between the amounts of rain and sunshine we might get this Autumn I can tell you about a big change to the look of the .

We have been working on this new look for a few months, and what you can see from today is just the beginning. Further changes and developments will be rolled out across the site over the coming months.

The changes to the design of the site have been largely driven by your feedback, either through our regular site surveys or the feedback forms we have put up on the site over the past couple of years. From the research it was clear that despite the many different ways the weather affects your lives the main thing you want from our site is the forecast (surprised - I guess not!).

But it was also obvious that improving navigation around the site and an updated design would be key elements in any revamp.

ÃÛÑ¿´«Ã½ News and Sport underwent a similar process earlier in the year and we have incorporated the best of the changes they made into the Weather site. Some of the changes are part of a new visual style that will apply across all the ÃÛÑ¿´«Ã½'s new and redesigned websites - the centering of the pages, the underlying layout grid, and the pan-ÃÛÑ¿´«Ã½ masthead.

So what are the main differences you'll see between the old and new sites?

The two biggest changes are the structure of the site and the visual design. All of our forecast information is now organised by location rather than by type of data. Once you have searched for your location you will find everything you need on one page. The visual design now follows the broadcast design, so the colour of the pages reflect the weather conditions for the location you are looking at.

Our forecast information is displayed in individual modules on a page and these can be expanded or collapsed depending on whether you are interested in the information or not.

Today's forecast for UK locations on the main Weather site are no longer depicted by one summary symbol. Today is covered by a three-hourly breakdown to show more clearly how the weather will change over the 24 hours to come.

Your feedback indicated that being able to personalise our site is important to you, so we have increased the number of locations you can save as favourites. The new site will also remember which modules you had open on your favourite locations last time you viewed them for the next time you visit.

Each location page displays the accompanying weather map, but you can also navigate to other map areas without leaving your page. This means you can choose a different or wider area map if you prefer.

Our website is now wider. The ÃÛÑ¿´«Ã½ has received feedback from you about making the best use of available screen space. We're confident that now is the right time to use the extra space to improve the site.

Remember this is work in progress so not all of the features we are developing will be there on day one - and I'll keep you posted on the upcoming changes over the next few months. A big improvement coming later this year will be embedded video forecasts. So whether you are looking at a UK forecast or for your holiday destination our familiar broadcast team will be there to talk you through the latest forecast.

So take a look around the new site, and let us know what you think.

As ÃÛÑ¿´«Ã½ Weather continues to extend its reach and range of services on television, radio, interactive, online and mobile it is becoming a hot topic of conversation as to whether we concentrate our efforts on working with the to improve the accuracy of the weather data or the consistency of that data between all of our services and platforms; of course in reality and over time we need to do both.

To assess where we have got to Claire Douglas, ÃÛÑ¿´«Ã½ Weathers Producer, data and graphics explains how the process for ingesting and delivering the weather data works:

"One of the major drivers for moving to a new Weather system in 2005 was to be able to provide consistent weather data throughout the ÃÛÑ¿´«Ã½.

Previously a significant amount of manual work was needed at the ÃÛÑ¿´«Ã½ Weather Centre; each forecaster/presenter would create a collection of slides and manually add symbols and temperatures to the core maps. This data was limited to that presentation and was therefore not shared across the website or Ceefax.

Our current weather system, provided by who are based in New Zealand, is set up to ingest weather data from the Met Office and push the information to all platforms as soon as it is available. Any changes made at the ÃÛÑ¿´«Ã½ Weather Centre or in the Nations and Regions are fed back to the central database and synchronised with all the databases, as well as Ceefax, the Weather website and applications such as Facebook."

This approach ensures a consistent message is available wherever you are viewing ÃÛÑ¿´«Ã½ Weather output. Progress continues, this week we have improved the updates from the weather database to the website for site specific information - every 30 minutes any changes to this information are delivered to the website at bbc.co.uk/weather to our mobile weather service, ÃÛÑ¿´«Ã½ Ceefax and to ÃÛÑ¿´«Ã½i.

We are questioned about our ability to be consistent but with the majority of our TV and radio output being live we have the opportunity to make changes right at the last minute - this means we are setting very high standards.

There is a balance to be struck and we are dealing with a continually developing weather story 24/7 but I believe that improvements in technology and speed of data transfer can only improve matters further in time.

Since the Easter weekend there has been a lot of discussion about the wintry weather. Viewers have been asking how unusual it was to get snow falling at Easter and we have been asking ourselves to what extent we got the weather story effectively across to the audience.

Part of this story was the use of the Feels Like temperature icons. These were used across the weekend to highlight the fact that the heavy snow showers were not the full story, rather the biting northerly winds would make it feel very much colder than the thermometer might suggest.

So is the data scientific? The answer is yes. The data is supplied by the who are using a well respected formula, the JAG/TI, to produce the temperatures for the winter season.

The JAG/TI algorithm, measures 'face only wind chill' and is one used in Canada. The Met Office use this formula as it has been clinically tested, it is simple to use and based on advances in science, technology, and computer modelling.

Specifically, the JAG/TI Wind chill Temperature index:

• Calculates wind speed at an average height of five feet (typical height of an adult human face) based on readings from the national standard height of 33 feet (typical height of an anemometer)
• Is based on a human face model
• Incorporates modern heat transfer theory (heat loss from the body to its surroundings, during cold and breezy/windy days)
• Lowers the calm wind threshold to 3 mph
• Uses a consistent standard for skin tissue resistance
• Assumes no impact from the sun (ie clear night sky).

The formula...
T(wc) = 13.12 + 0.6215T - 11.37V**0.16 + 0.3965TV**0.16

(Where T(wc) is the wind chill index based on the Celsius scale, T is the air temperature in °C, and V is the air speed in km/h measured at 10 m (33 ft, standard anemometer height).

Why is it called Feels Like? Our aim was to find a way to provide a quick indication of what it would Feel Like when you step outside all year round. This winter has seen the first use of Feels Like but we have been using wind chill for many years. The difference now is that it will be used in the summer during periods of extreme heat. Although the formulas used to calculate the temperatures are different depending on whether it is summer or winter, ultimately the end result is the same – what it will Feel Like.

At the end of the day we will be using it when it helps give the complete weather picture. It might be bright sunshine out of the window, and the thermometer may read 5C but if there is a breeze, then it will feel colder than 5C and this might have an impact on what people want to wear. As with our wind graphics and isobar charts we will use these graphics when relevant to the weather story of the day.

The branding of the white temperature disk and blue square outline is a recent development on the weather graphics system, introduced in 2005. It was developed from the previous wind chill graphics - a blue temperature and a yellow outline – to fit in with the current look and feel of the weather graphics.

After Monday's weather warnings, our dilemma at the ÃÛÑ¿´«Ã½ Weather Centre today is warning fatigue. Forecasters at the Met Office have issued an early warning of severe gales with potentially damaging gusts for late Tuesday into Wednesday. The question is, will viewers listen to today’s message?

The difference from Monday's event is that more areas are likely to be affected than on Monday. The strongest winds are expected to reach Northern Ireland late on Tuesday evening, and then transfer across parts of southwest Scotland, northern England, north Wales and the Midlands during Wednesday.

Gusts of 65 to 75mph are expected with the possibility of gusts in excess of 80mph on exposed coasts and hills, especially across Northern Ireland and northwest England. Further disruption to transport networks and power supplies is possible and there is the potential of damage to buildings and trees.

As a further complication the winds are expected to be accompanied by some heavy snow over the higher parts of northern England and southern Scotland.

So, how do we continue to get the message out without viewers feeling that it's just another warning? Following our morning briefings with the Met Office and discussions with our colleagues here at TV Centre it is clear that tonight’s event is very serious and could lead to even more disruption than on Monday.

Confidence is high at the Met Office that wind strengths could exceed 80mph and as a result we are leading our national weather bulletins with the early warning and making sure that the message is getting out across all of our services.

With each run of data we continue to monitor the situation and increase the emphasis for the potential of damage and disruption.

At 5.10am, as I left the house in Folkestone this morning, I had an appreciation of how bad the weather was going to be – I knew from the weekend forecast that the worst would be along the south coast, with breakfast time being the peak and I wasn’t let down. The train into London was buffeted all the way with several pieces of debris on the track causing some concern.

Forecasters at the Met Office were alerting us as early as last week, and yesterday the areas for likely disruption were clearly identified. But the gales were not the full story, as the strong winds coincided with spring high tides, increasing the risk of coastal flooding.

At the ÃÛÑ¿´«Ã½ Weather Centre we have to weigh up the need to give viewers a steer on what is ahead but balance that with crying wolf. On Sunday we were confident that the winds would be strong but exactly who would be in the firing line needed to be watched. The Met Office computer model is run every six hours and with each successive run we monitored the track and intensity, firming up on the forecast.

When I arrived at TV centre the weather team were already in full swing with Matt Taylor on Breakfast and Chris Fawkes on Radio 4.

The winds were expected to continue to gust to 75 to 85mph at times though the rest of today especially in exposed locations. The weather team were reporting on the current weather situation using the latest satellite and radar data with league tables of the highest gusts. Our durations were extended on ÃÛÑ¿´«Ã½ News 24 to two minutes 30 seconds so that we could provide the additional details required. The worst hit areas were parts of Wales, western and southern parts of England where all emergency services were put on alert.

As the stormy weather lashed parts of the country, leaving homes without power and disrupting travel, the team kept updating the forecast and bringing the very latest information to viewers on TV, radio, online and mobile. The highest reported gust was 95mph on the Isle of Wight at the time of writing and this news was first to air on the One O’Clock News with Kirsty McCabe.

Very few places escaped the bad weather with northern parts of the UK seeing both rain and snowfall – up to 15cm was forecast over the Scottish Highlands.

As the thunder rumbles around TVC, the word is that more gales are on the way for Wednesday – so keep watching!