No prediction for a ‘decade of washouts’

8 07 2013

An article by Jon Ungoed-Thomas in yesterday’s Sunday Times talks about the recent spell of fine weather in contrast to an apparent “prediction” from the Met Office of a “decade of soggy summers”.

This is despite the Met Office making it very clear that it did not issue any such prediction.

The article follows up on media coverage of a science workshop held at the Met Office in June this year to look at the recent run of unusual seasons in the UK.

During the press conference held after that meeting, research from the University of Reading was raised – you can read more about that on our blog.

The following press coverage was mixed, with some media outlets accurately representing the research, while others portrayed it as a forecast for a decade of washout summers. We discussed this in a blog the next day.

Here’s a couple of key highlights quotes directly from that blog article:

• [This research] does not mean every summer will be a ‘washout’ for the next decade and shouldn’t be taken as a deterministic forecast for what we will see in the years to come.

• [The] research suggests there is a tendency towards a higher frequency of wetter than average summers – so we could still see summers which buck this trend.

• [This] research is still at an early phase and more work needs to be done to see exactly how this process works and how we can predict its influence on future seasons… it’s fair to say that you shouldn’t write off summers for the next decade or so.





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.”





Media coverage on ‘wet summers for a decade’

19 06 2013

There has been a lot of media coverage today following a science workshop held at the Met Office HQ in Exeter yesterday.

Most of the articles go some way to capturing the science as it was delivered in the press briefing following the event – such as this article on the BBC News website. However, some stories, and particularly some headlines, do not.

The key point revolves around discussion of Atlantic ocean cycles, specifically one known as the Atlantic Multidecadal Oscillation (AMO), which can have an influence on UK summer weather.

Professor Stephen Belcher, Head of the Met Office Hadley Centre, and Dr James Screen, a NERC Research Fellow at the University of Exeter, were careful in their messaging about the AMO.

They talked about initial research which suggests this cycle, which can last for 10-20 years, can ‘load the dice’ to mean we may see a higher frequency of wetter than average summers before switching to its opposite phase, where we may see the opposite effect.

Currently, they said, it appears we are well into the ‘wet’ phase of this cycle, so it may continue to have an influence for a few more years to come.

That does not mean every summer will be a ‘washout’ for the next decade and shouldn’t be taken as a deterministic forecast for what we will see in the years to come.

First of all, we’ve seen five summers of higher than average rainfall in the last six years (with 2010 being the exception, which had average levels of rainfall). Even within each of those years we have seen periods of decent weather – so there’s no expectation of total washouts for the whole summer.

Secondly, the research suggests there is a tendency towards a higher frequency of wetter than average summers – so we could still see summers which buck this trend.

And finally, this research is still at an early phase and more work needs to be done to see exactly how this process works and how we can predict its influence on future seasons.

So, much like a blog we recently wrote about this year’s summer, it’s fair to say that you shouldn’t write off summers for the next decade or so.

We expect to be publishing a guest blog from scientists at the University of Reading on the science they presented to the workshop yesterday, so look out for that in the coming days.

You can now see video of the Professor Stephen Belcher speaking at the press conference which followed the science workshop on 18 June on our Youtube channel.





The jet stream and why it’s too early to write-off summer

13 05 2013

There have been one or two stories in the press today saying we’re in for another washout summer, which would rightly inspire collective misery across the country.

However, it’s a far too early to be writing off any chance of a decent summer season – after all, it doesn’t officially start (for us meteorologists) for more than two weeks (on 1 June).

It appears the news stories are borne out of the current position of the jet stream, a band of fast moving westerly winds high up in the atmosphere. But why is this important?

A quick Jet stream explainer

The jet stream tends to guide the generally wet and windy weather systems which come in off the Atlantic. So, if it’s over us or just to the south, we tend to get a lot of wet and windy weather – which is what we expect through winter.

If the jet is to the north of us, it guides that changeable weather to the north to give us more settled conditions – which is what we expect in the summer.

(You can read a bit more about the jet stream, how it impacted our weather last year, and any potential connections to climate change in a blog story we wrote last year).

What’s going on now?

Right now the jet stream is sitting to the south of the country and it is influencing the unsettled weather we are seeing at the moment.

Forecast chart showing position of the jet stream at midday on 13 May 2013

Forecast chart showing position of the jet stream at midday on 13 May 2013

It’s fair to say that this is roughly the position it was in for extended periods during the exceptionally wet weather that we saw last year, particularly in June.

Crucially, however, the jet stream does move around quite a bit and it can change its track significantly in just a few days. So the current position of the jet stream does not mean that it’s stuck in that position.

Looking ahead

Much like our weather, it’s a huge challenge to predict the exact track of the jet stream more than five or six days ahead, so there’s still a great deal to play for in the outlook for our summer.

In short, it’s far too early to write-off summer 2013 based on the current position of the jet stream.

To get the best information on what to expect you can see the latest detailed forecasts out to 5-days on our website, 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.





The UK’s wet summer, the jet stream and climate change*

12 07 2012

There’s no disputing it has been a very disappointing summer so far in 2012 – with the wettest June for over a century followed up by a very wet start to July.

In fact, barring a warm and dry spell towards the end of May, the weather has been persistently dull and wet since April – which was also the wettest in records dating back to 1910.

Our weather here in the UK is complex and determined by many different factors, including the position of the jet stream.

This is the narrow band of fast moving winds which runs from west to east across the Atlantic high up in the atmosphere.

How does the jet stream affect UK weather?

Weather (or low pressure) systems bearing rain and unsettled conditions move across the Atlantic on a regular basis. The jet stream guides these systems, so its position is important for UK weather.

In summer, we would expect the jet stream to be north of the UK – dragging those weather systems away from our shores to give us relatively settled weather.

So far this year it has been to the south of the UK, guiding those systems straight to us. This is the position we’d normally expect the jet stream to be in during winter, when we are more accustomed to these wet conditions.

So why is the jet stream stuck so far south?

The jet stream, like our weather, is subject to natural variability – that is the random nature of our weather which means it is different from week, month or year to the next.

We expect it to move around and it has moved to the south of the UK in summertime many times before in the past. It has, however, been particularly persistent in holding that position this year – hence the prolonged unsettled weather.

This could be due to natural variability – a bad run of coincidence, if you will – but climate scientists are conducting ongoing research to see if there are other factors at play.

Changes in sea surface temperatures due to natural cycles may be playing a part, but there is more research to be done before anyone can establish how big a role they play.

Research has also suggested that reducing amounts of Arctic sea-ice could be affecting weather patterns, but more research needs to be done to confirm this link. Currently Arctic sea-ice is at a record low for this time of year.

Is climate change playing a role?

In the long term, most climate models project drier UK summers – but it is possible there could be other influences of a changing climate which could override that signal on shorter timescales.

If low levels of Arctic sea ice were found to be affecting the track of the jet stream, for example, this could be seen as linked to the warming of our climate – but this is currently an unknown.

The Met Office Hadley Centre, working with climate research centres around the world, is making strides in determining how the odds of extreme weather happening have been influenced by climate change.

However, it is very difficult to do this type of analysis with such highly variable rainfall events, so it may take many years before we could confirm how the odds of this summer’s wet weather happening have been altered by greenhouse gases.

We do know that the warmer air is, the more moisture it can hold. We have seen a global temperature increase of more than 0.7 deg C (since pre-industrial times) and this has led to an increase of about 4-5% in atmospheric moisture.

This means that when we do get unusual weather patterns such as we’re seeing now, it’s likely there will be more rainfall than the same patterns might have produced in the past. In short, it seems when it does rain, it is heavier.

Taking into account this effect, perhaps it’s not surprising new records like those for this April and June are being set. In fact, the wettest July and November in the records dating back to 1910 happened in 2009, making a total of four record wettest months in the past four years. If wet months occurred randomly, we would expect only one record to have been broken since 2006.

For temperature, April (2011), May (2008), July (2006), September (2006) are all recent warmest records. Again, this is much more frequent than would be expected if temperatures were not rising.

What about elsewhere in the world?

Looking at the bigger picture, the jet stream may be having an impact elsewhere in the northern hemisphere.

It is stuck in a persistent pattern of waves, with one of these ‘waves’ taking it to the south of the UK.

Figure shows upper level wind patterns in early July 2012, with the northern hemisphere jet stream marked with arrows.

The figure gives a picture of the upper level winds for the first week in July, but the wavy nature of the jet stream has been persistent throughout June.

Meanders of the jet north and south can be seen across the US, the Atlantic and into Europe.

While the wet weather in the UK has been under a southward meander of the jet stream, the recent Russian floods near the Black Sea appear to have been beneath the next trough to the east.

The US heat wave is also beneath a northward meander and a ridge of high pressure.

* This article has been written in collaboration with the Walker Institute for Climate System Research, University of Reading.





Heavy rainfall across parts of the UK

23 06 2012

The past two days have seen some exceptional rainfall across the UK, with the heaviest and most persistent rain falling in the North West of England, parts of Northern Ireland and parts of southern Scotland.

Across this area there have been fairly widespread rainfall totals of about 25-50mm of rain in the past 24 hours – from 10am yesterday (22 June) to 10am this morning.

However, some spots saw even more rain in the same period. Here are the wettest places in the past 24 hours:

Blencathra, Cumbria – 93.8mm

Keswick, Cumbria – 88.6mm

Stonyhurst, Lancashire – 74.4mm

Levens Hall, Cumbria – 58.2mm

Morecambe, Lancashire – 57mm

Walney Island, Cumbria – 55.8mm

Preston, Lancashire – 54.8mm

Myerscough, Lancashire – 52.2mm

Bingley, West Yorkshire – 50.2mm

This is in line with the yellow and amber Severe Weather Warnings issued by the Met Office for yesterday’s rain, which forecast 25-50mm of rain across a wide area and up to 100mm possible in some spots.

Rainfall has eased this morning, however heavy rain is expected to sweep in across the UK later this evening and into tomorrow morning and the Met Office has issued further weather warnings.

You can stay up to date with the latest situation by looking at the warnings pages on our website and by staying up to date with our forecasts.

Later on Sunday the weather is expected to improve, giving way to a drier and brighter start to the week with sunny spells and improving temperatures.








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