So what happened to our summer?

28 08 2015

Our Chief Scientist Professor Dame Julia Slingo OBE FRS reflects on this summer’s weather and what has influenced it:

No-one can deny that we have had a pretty disappointing summer with a lot of unsettled weather and only a few warm spells, especially through July and August. Our weather has been dominated by low pressure over and to the west of the country that has brought us periods of heavy rain from the south – what we call the Spanish Plume. So what has been happening?

If we look beyond our shores there have been some big changes in the global climate this year. El Niño is in full flight, disturbing weather patterns around the world. The low pressure that has dominated our weather is part of a pattern of waves in the jet stream around the world that has brought crippling heat waves to places like Poland and Japan. And, looking back over past El Niños, you could have expected that a more unsettled summer might be on the cards for the UK. Closer to home the North Atlantic is more than 2 degrees colder than normal. It seems quite likely that the unusually cold North Atlantic has strengthened and pushed our jet stream south, also contributing to the low pressure systems that have dominated our weather.

So could all this have been anticipated? Seasonal forecasts for this summer suggested that temperatures and rainfall would be near normal. However, as the season progressed all the leading models around the world failed to capture the signal for unsettled weather over the UK. We all know that forecasting months and seasons ahead is still in its infancy and much more research needs to be done. On the other hand our day-to-day forecasts have been really successful in allowing us to warn of bad weather, highlighting yet again the benefits of our research that has delivered year-on-year and decade-by-decade improvements in forecasting skill. Our 5-day forecast is now as accurate as our 1-day forecast was when I started my career. This enables us to make so many decisions that keep us safe, protect our property, keep our infrastructure running and even when to go out and enjoy the sunshine!

All of this cannot happen without improvements to research and technology, and this week the first phase of our new supercomputer went live, five weeks ahead of schedule. This will enable us to provide even more accurate and relevant weather and climate forecasts to all of us, our government, emergency responders, and our many other customers at home and abroad.

The news that the BBC has decided that the Met Office won’t be their main weather provider when the current contract ends has raised the question of where will the new provider get their information from. It’s important to understand that no weather forecasting organization, whether it is a National Met Service like the Met Office or an independent company, can provide a service without a forecast, and that it is the leading meteorological agencies, like the Met Office, that build and deliver those forecasts. So whoever the BBC chooses to deliver their weather services in future, you can be sure that Met Office observations and forecasts will continue to be at the heart of them. We are committed to driving forward the skill and usefulness of our forecasts and ensuring that all of us benefit from the advances the Met Office makes in the coming years with our new supercomputer.





One year on – A look back to last winter

17 02 2015

This weekend marked the one-year anniversary of the Valentine’s Day storm, which also marked the end of a particularly stormy three-month period. A new review article – ‘From months to minutes – exploring the value of high-resolution rainfall observation and prediction during the UK winter storms of 2013/2014’ – written by 16 Met Office co-authors reviews the accuracy of our forecasting and warning of severe weather during winter 2013-14, and assesses its performance.

The paper concludes that the “prolonged period of high impact weather experienced in the United Kingdom during the winter of 2013/14 was very well forecast by the operational tools available across space and time scales.”

Here Huw Lewis, the paper’s lead author, and Derrick Ryall, Head of the Public Weather Service, look at the extreme weather last year and the role of the Met Office in communicating severe weather through the National Severe Weather Warning Service.

Analysis chart 1200 GMT 26 January 2014

Analysis chart 1200 GMT 26 January 2014

Winter 2013/2014 in the United Kingdom was remarkable. The country was battered by at least 12 major winter storms over a three month period and was officially assessed as the stormiest period that the United Kingdom has experienced for at least 20 years.

The series of storms resulted in the wettest winter in almost 250 years (according to the England and Wales precipitation series from 1766), significantly wetter than the previous wettest winter in 1914/1915.

Snapshot of UK rain radar surface rainfall rate for 2200 GMT on 23 December 2013

Snapshot of UK rain radar surface rainfall rate for 2200 GMT on 23 December 2013

The extreme weather caused widespread flooding throughout Southern England and coastal damage – most notably in the South West and Norfolk coasts. The impact of the severe winter storms on individuals, businesses and the government were substantial, including several fatalities, widespread power cuts and damaged infrastructure.

Recent advances in forecasting, technology and the scientific developments in meteorology have been considerable. These developments and improvements in accuracy mean that a four-day weather forecast is as accurate as a one-day forecast was just thirty years ago. During the course of last winter, the Met Office was able to use these forecasts to warn of any severe weather well in advance. In the case of the St Jude’s Day storm at the end of October 2013 warnings went out to the Government and the public five days before the storm even existed.

rainfall

As the accuracy of weather forecasts has evolved, so has the communication of the potential impacts of severe weather. The National Severe Weather Warning Service enables more ‘weather decisions’ which in turn help to minimise the consequences of severe weather. The Met Office was at the heart of the government response to the storms, providing advice on weather impacts through the National Severe Weather Warning Service and Civil Contingency Advisors. The Met Office also worked very closely with both the national and regional media, who in turn played a key role in ensuring that the public were fully informed about the potential impacts of any up-coming weather.

In addition to the Public Weather Service, commercial partners and customers were also provided with detailed updates throughout the period in order for them to plan effectively for logistical issues. Together, these advanced warnings helped authorities, businesses and individuals to be better prepared to take mitigating actions.

Driving further improvements in accuracy and therefore reducing the lead time and increasing the detail of severe weather warnings is one of the Met Office’s key priorities . The ultimate aim is to improve the potential for users to plan preventative measures for severe weather events much further ahead. Underpinning all of these developments is a continuing programme of scientific research and access to enhanced supercomputing over the next few years.





Why are we now seeing colder weather across the UK?

16 01 2015

Over recent weeks, we have spoken about the very strong jet stream across the Atlantic, driving areas of intense low pressure towards the UK. This has bought spells of very wet, windy but relatively mild conditions to the country.

As many of you would have noticed, although the wind and heavy rain has eased, there is now a colder feel to the weather, both by day and night. But what has caused this change in the weather?

Once again the change is down to the jet stream. It has weakened and its track has moved further south, keeping the deep low pressure systems away from our shores. However, now the UK is to the north of the jet stream we are on its cold side, and this has allowed colder weather to feed in across the country.

Current jet stream

Current jet stream across the Atlantic

So what does this mean for us?

As we look ahead into the weekend and next week, the cold weather looks likely to continue. Daytime temperatures will be near or below average and there will be some frosty nights, as temperatures fall below freezing in many areas. We’ll see some sunny spells around and there will also be showers or longer spells of precipitation in places, giving a mixture of rain, hail, sleet or snow, which may settle in some areas.

Because of the threat of wintry weather over the coming days, we encourage everyone to keep up to date with the latest forecasts and national severe weather warnings and to stay weather aware this winter by following the Met Office on Twitter, Facebook, Google+ and YouTube for the latest weather information. You can find information about how to prepare for every aspect of the winter season at Get Ready for Winter.

As we head towards the latter part of the month, we can see some indications that milder weather may return, but there is considerable uncertainty about this so far in advance.





How a strong jet stream is affecting aviation

13 01 2015

We often talk about the jet stream and its impacts on UK weather – but it can have an even more direct effect on aviation as covered in the media in recent days.

The jet stream is a band of fast moving winds high up (around 5-7 miles) in the atmosphere. It usually travels eastwards around the northern hemisphere but regularly changes its track and strength.

Pilots travelling east, say from the US back to Europe, use the jet stream to cut journey times and save fuel – just like a cyclist uses a tailwind on a bike.

This has always meant journey times in the northern hemisphere are faster when travelling east than heading west (when airlines avoid the jet stream).

Recently the jet stream has been particularly strong over the north Atlantic, with winds of more than 250mph being seen at times.

You can find out more about the jet stream in our YouTube video:

This has had an impact on flying times – with eastbound trans-Atlantic services arriving well in advance of their scheduled times. Some types of passenger aircraft have reputedly seen record breaking journey times.

All this of course has a knock-on effect for airports as schedules are carefully planned to ensure there’s room, not to mention boarding gates, for each aircraft when it’s due to land. That has meant the strong jet stream creates a logistical challenge for airports across Europe.

The Met Office has been helping airlines and airports to plan ahead with its forecasts of the strength of the jet stream through its role as a World Aviation Forecasting Centre (WAFC).

There are only two WAFC centres in the world; the UK and Washington, in the US. The two centres provide aviation charts for the globe, highlighting conditions between 10,000 and 63,000 feet.

These charts show the location and strength of the jet stream, as well as other important aviation factors, such as clear air turbulence, cumulonimbus (storm producing) clouds, volcanoes and tropical storms. Both centres operate 24 hours a day and throughout the year.

Airlines use our upper-air wind forecasts to predict flight times at cruising altitude. For transatlantic flights during 2012, the average difference between the predicted flight time and the actual flight time was about one minute. This means that our aviation customers can accurately calculate the fuel load required for each flight. Our WAFC charts save airlines globally £2.7 billion a year because our forecasts help them fly safely and efficiently.

Accurate forecasts enable pilots, airlines and airports to assess flying times in advance and use that information to try to ensure things run as efficiently as possible on the ground.





US snowfall and will it impact the UK?

20 11 2014

Parts of the US and Canada are seeing particularly cold weather and heavy snowfall at the moment.

Chart showing the position of the jet stream over North America as at 00:01 on 20 November.

Chart showing the position of the jet stream over North America as at 00:01 on 20 November.

A southward buckle in the jet stream has seen cold polar air flow south to north eastern parts of North America.

In the Buffalo region of New York state, temperatures have fallen as low as -15C and 4-5 ft (about 1.5 metres) of snow has fallen – enhanced by what’s known as the ‘lake effect’. Another 2-4 ft (about 1 metre) is expected through today.

The snowfall is set to ease on Friday with much milder conditions through the weekend giving a rapid and significant thaw – which could bring a risk of flooding.

This risk could increase through the start of next week when some very heavy rain is expected across the area.

What is lake effect snow?

Lake Superior (top left) and Michigan (centre) can be seen generating 'lake effect' snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

Lake Superior (top left) and Michigan (centre) can be seen generating ‘lake effect’ snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

This is an effect which applies to areas around large lakes like those seen in the northern US – Lake Superior has an area of more than 30,000 sq miles.

When cold air moves across the relatively warm waters of the lake, air rises due to convection which creates clouds and heavy showers. In cold conditions, the moisture in the clouds will fall as heavy snow.

As Buffalo as it the eastern tip of Lake Erie it has been particularly susceptible to this effect during the recent weather.

While we don’t have any lakes big enough for this effect in the UK, we can occasionally see a similar scenario when we get easterly winds in the winter.

Cold air from the continent can be warmed by the relatively warm North Sea as it moves across the water, bringing snow showers to eastern parts of the UK. However, there’s no sign of this in the immediate future for the UK.

Will the US weather affect the UK?

Many people believe that there’s a rule of thumb that weather in the US will arrive in the UK a few days later – but that’s by no means always the case.

In this instance, there’s high confidence that the cold snowy weather will stay on the western side of the Atlantic.

Also, in past winters similar weather situations in the US have strengthened the jet stream and increased the risk of storms across our shores. Again, in this instance, this isn’t expected at the moment.

What we do expect to see is further changeable weather over the coming few days.





What is causing the extreme cold over North America?

7 01 2014

The weather over North America has been hitting the headlines over the last few days with record breaking cold conditions spreading south from the Arctic. This has been linked to a ‘polar vortex’, but what is this and what could it mean for the UK?

What is the Polar Vortex?

The Polar Vortex is a term normally used to describe the persistent large-scale low pressure area situated around 50km above the poles in the stratosphere. When the vortex breaks down the eastern US is often cold, but this breakdown hasn’t happened yet. It is not clear to what extent the Polar Vortex is influencing surface weather at the moment.

What is happening over the USA?

The American use of the phrase ‘polar vortex’ referring to the extremely cold conditions over North America is slightly different to traditional definition above. It refers to features lower in the atmosphere – in the troposphere, where our weather happens.

In the winter a deep reservoir of cold air becomes established through the atmosphere over the Arctic because of the lack of sunlight. This is usually held over high latitudes by the jet stream.

What is happening over North America is that the jet stream has weakened and moved southwards in the wake of a low pressure system as it moved east over the Atlantic.  This allowed the reservoir of cold air to move southwards across the US, resulting in extremely low temperatures.

What does it mean for the UK? Does it mean it will get cold here?

Not at the moment. We get our coldest weather in the winter when the winds blow from the northeast or east – so from the continent.

In fact the cold weather in the US can strengthen the jet stream and bring the UK milder and wetter weather, much as we have seen over the last few days.

Currently our winds are blowing from the west and, while we will see the temperatures dropping from the mild conditions we have had during December, they will only be returning to something much closer to normal for the time of year.





Our change in the weather and how the jet stream is driving it

13 12 2013

After a quiet spell of weather courtesy of a slow moving area of high pressure, we are now entering an unsettled period as a series of Atlantic depressions are expected to pass close to the northwest of Britain during the next week.

High pressure has now moved away and is settled over Europe and a powerful jet stream is developing over the Atlantic which will be the main driving force behind this spell of unsettled weather.

What is the jet stream?

The jet stream is a band of fast moving westerly winds high up in the atmosphere which circle around the pole in the northern hemisphere. It can feature winds of up to 200 knots (230 mph) or more, and these winds tend to guide wet and windy weather systems which come in off the Atlantic.

The jet moves around a fair bit and its position can have a big impact on weather here in the UK depending on where it is.

If the jet is over the UK or just to the south, we tend to get a lot of wet and windy conditions as it brings weather systems straight to us. If the jet is to the north of us, it guides that changeable weather away to the north to leave the UK with more settled conditions.

What’s the jet stream doing now?

Unsurprisingly given the outlook for the next week, with a succession of Atlantic depressions passing by to the northwest of Scotland, the jet is positioned to the northwest of the UK too.

As you can see from the picture below, the jet currently swoops east from Canada – swinging northeast over the Atlantic towards the UK.

Forecast position of jet stream at midday Saturday 14 December 2013

Forecast position of jet stream at midday Saturday 14 December 2013

Closer to the ground very cold air is also streaming south from Canada and meeting warm air moving north from the Caribbean. It is where these two air masses meet under the jet stream that powerful Atlantic depressions form and are blown across the ocean towards our shores.

It is these depressions that bring a significant risk of severe gales and heavy rain affecting at least the northwest of the UK at times.

What’s the weather outlook?

Currently, Met Office National Severe Weather Warnings have been issued for wind across some northwestern and northern areas for the weekend. Gusts of 60-70 mph are likely with a risk of gusts to 80 mph or more across exposed parts of northwest Scotland.

However, at this stage there remains uncertainty regarding the extent of the strongest winds and these warnings will be updated as the weather develops over the weekend.

Looking ahead, while we expect further depressions to develop it is not possible to say exactly how vigorous they may be or pinpoint where they will be in a week’s time. This means it is too early to say which areas will experience the strongest winds and heaviest rain, however there are indications that  areas further to the south of the UK may be affected at times.

You can stay up to date with what to expect with our detailed forecasts out to 5-days and our weather warnings, as well as a general view of what we expect out to 30 days and find out what to do in severe weather

You can find out more about the jet stream in our YouTube video.

 





UK’s unsettled weather and the jet stream

21 10 2013

The UK is set to see unsettled weather throughout this week as heavy rain and windy conditions are expected to affect many areas, whilst temperatures will remain mild for the time of year.

We talk about the jet stream quite a bit in the UK because it has such a big influence on our weather, and this week is no exception as it’s playing a leading role in determining the unsettled outlook.

What is the jet stream?

The jet stream is a band of fast moving westerly winds high up in the atmosphere which circle around the pole in the northern hemisphere. It can feature winds of up to 200 knots (230 mph) or more, and these winds tend to guide wet and windy weather systems which come in off the Atlantic.

The jet moves around a fair bit and its position can have a big impact on weather here in the UK depending on where it is.

If the Jet is over the UK or just to the south, we tend to get a lot of wet and windy conditions as it brings weather systems straight to us. If the jet is to the north of us, it guides that changeable weather away to the north to leave the UK with more settled conditions.

What’s the jet stream doing now?

Unsurprisingly given the outlook for this week, the jet is positioned more or less directly over the UK – but it’s the detail of its track which is important.

As you can see from the picture below, the jet currently swoops south from western Canada – moving over the Atlantic before taking a sharp turn north to head over the UK.

Forecast chart showing  expected position of the jet stream at 1pm on Tuesday 22 October

Forecast chart showing expected position of the jet stream at 1pm on Tuesday 22 October

This means relatively cool air is being dragged south then over the Atlantic, where warmer seas heat the air from below. This causes the air to warm and rise – creating instability and generating cloud and rain.

By the time weather systems reach they UK they have picked up a lot of rain and relatively warm air, bringing us the wet but mild conditions we are currently seeing.

What’s the weather outlook?

Currently unsettled weather looks set to impact the UK through the week, with heavy rain affecting many areas at times.

There may be more settled conditions on Thursday, and perhaps again on Saturday, but looking further ahead into the start of next week the outlook is for unsettled weather to continue.

You can stay up to date with what to expect with our detailed forecasts out to 5-days and our weather warnings, as well as a general view of what we expect out to 30 days.

You can find out more about the jet stream in our YouTube video.





Jet stream shift to bring summer weather

1 07 2013

It’s usually true to say that confidence in a weather forecast decreases the further out you look.

However, we have a situation at the moment where we are actually more confident in the detail for this weekend and beyond rather than over the next few days.

This is because we are seeing some very strong signals for high pressure to dominate the weather from around Friday and then persist for several days afterwards.

In summer high pressure means fine weather, and it also looks like it will become very warm as well.

Normally we can’t give much detail beyond the 5-day forecast period, but with the current situation we can give a forecast beyond that with a higher than usual level of confidence.

So for, say, the Men’s Wimbledon Final on Sunday it looks like it will be dry and very warm with a good deal of sunshine. We are less confident in predicting who will be in the final, or who will be the winner, though.

As we go through into next week, it looks highly likely that one or two places will nudge towards the 30 C mark.

With this in mind, it’s likely that by the middle of next week we’ll have topped the current warmest temperature of the year, which was 27.2 C recorded at Heathrow yesterday (Sunday, 30 June).

So why will we be seeing high pressure develop over the UK to give us this spell of fine weather?

Well, to get this type of situation we need the jet stream to be in the ‘right’ place for this time of year – tracking to the north of the UK between Iceland and NW Scotland.

Chart showing expected position of the jet stream on 6 July 2013.

Chart showing expected position of the jet stream (shown in shades of green) on 6 July 2013.

In this position it guides rain-bearing Atlantic low pressure systems off to the north of the country, meaning the far north-west of the UK gets glancing blows from these systems while the rest of the country has more settled conditions.

We expect the jet stream to move into this position over the next few days.

Leading prediction models from forecasting centres around the world all seem to be in agreement about this development – hence the unusually high level of certainty in the forecast. But, of course, forecasts can still change – so do stay in touch with the latest in our 5-day outlook and out to 30-days ahead.





Guest blog – How the Atlantic may influence wet summers

19 06 2013

This morning there has been a lot of media coverage following a workshop held here at the Met Office HQ in Exeter on a recent run of unusual seasons in the UK.

Much of this centred around recent research by the University of Reading, presented at the workshop yesterday, which suggested Atlantic ocean cycles – specifically one known as the Atlantic Multidecadal Oscillation (AMO) – can have an influence on UK summer weather.

Here Professor Rowan Sutton, from the University of Reading, explains that research in a bit more detail:

 

“Last year, Buwen Dong and I at the National Centre for Atmospheric Science published a paper in Nature Geoscience about the link between slow changes in the temperature of the North Atlantic Ocean and weather patterns.

In particular, we presented evidence of a link between warm surface temperatures in the North Atlantic and a higher frequency of wet summers in the UK and Northern Europe.

This research built on earlier research I published with another colleague, Dan Hodson, in Science in 2005 and an important study by Jeff Knight and colleagues at the Met Office, which was published in 2006.

In our 2012 paper we showed that a rapid warming of the North Atlantic Ocean which occurred in the 1990s coincided with a shift to wetter summers in the UK and northern Europe and hotter, drier summers around the Mediterranean. The pattern identified matched that of summer 2012, when the UK had the wettest summer in 100 years.

Observational records show that the surface temperature of the North Atlantic has swung slowly between warmer and cooler conditions, and the present warm phase has a similar pattern to warm conditions that persisted throughout the 1930s, 40s and 50s. During the 1960s, 70s and 80s cooler conditions prevailed.

Computer simulations suggest that these changes in ocean temperature affect the atmosphere above. Warmth in the North Atlantic causes a trough of low pressure over western Europe in summer and steers rain-bearing weather systems into the UK.

An important question of interest to many people is how long will the current pattern of wet summers in northern Europe persist? This is a key research question and we don’t yet have precise answers.

In our 2012 paper we stated: “Our results suggest that the recent pattern of anomalies in European climate will persist as long as the North Atlantic Ocean remains anomalously warm.”

How long might this be?  There is strong evidence linking the swings in the Atlantic Ocean surface temperature to the “overturning” or “thermohaline” circulation of the Atlantic.

This circulation appears to have intensified in the 1990s. Following such a strengthening, a subsequent weakening is expected, as various feedbacks exert their influence.

For example, the surface warm waters transported northward by the overturning circulation have relatively low density which inhibits their tendency to sink, and acts to slow the circulation. Such a slowing cools the North Atlantic.

The time scales involved are in the range between a few years and a decade or two.  Progress in Decadal Forecasting, such as the pioneering work at the Met Office, and critical observations such as from the NERC-funded “RAPID” array, should help us to reduce this large range of uncertainty, but it is a challenging problem and advances may take some years.”








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