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A fascinating piece of research has been published in the journal Science today.

The article could go some way in explaining why global warming has slowed down in the last 10 years or so, , with a more detailed analysis you can read here.

The study by scientists at the US National Oceanic and Atmospheric Administration looked at water vapour (the most powerful greenhouse gas of all) in the stratosphere. Satellite measurements showed that water vapour levels in the stratosphere have dropped 10% since 2000, and when this was fed into a climate model, could have reduced by 25%, over the last decade, the amount of warming that would ordinarily be expected from greenhouse gases.

Their conclusion? The decline in stratospheric water vapour after 2000 should be expected to have significantly contributed to the flattening of the global warming trend in the last decade.

So the 6 million dollar question is this: Was this a natural change in levels of this powerful greenhouse gas. Or did global warming itself, particularly in the 1990's, cause this drop in stratospheric water vapour in the last decade? If so, could we be seeing natural processes putting a brake on global warming?

You can read more detail about this, including what scientists discovered happened to water vapour during the warming that occured during the 1980's and 1990's

In it, Susan Solomon who led the research says 'This (new study) shows there are climate scientists round the world who are trying very hard to understand and to explain to people openly and honestly what has happened over the last decade.'

Click on the text highlighted in blue to link to relevent article

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A lot of you have sent me e-mails asking me the same question: Will we see a return to the cold and snowy conditions that affected us a few weeks ago?

Over the next 24 hours an Arctic northerly will develop, as predicted by the various worldwide weather models in my update on Sunday, with a cold weekend in prospect.

Longer term as you might expect forecasting is a much more difficult job to get right, but there are signs of what might lie in store.

We have already discussed stratospheric warming in previous blogs. The idea is that extra warmth in the stratosphere can cause a blocking type of weather to develop in the troposphere, the area of the atmosphere where weather patterns affect us. Well, stratospheric warming commenced last week. This suggests that a blocking pattern of weather is possible into February.

Other indicators we look at are pressure patterns across the Arctic and the North Atlantic. Both the North Atlantic oscillation (NAO) and the Arctic oscillation (AO) have gone into their negative phase again, having temporarily turned positive around the middle of the month - and are forecast to stay that way into early February.

Without getting too technical, both these pressure pattern changes suggest that the jet stream could be pushed to the south of us once more, leaving us susceptible to colder air, with high pressure likely to build to the north of us - dragging cold air across us from the east.

None of these 3 features are a guarantee of a prolonged cold spell of weather - but the balance of probabilities are now tilting towards this being the most likely scenario.

The final piece of the jigsaw is the ensembles, again mentioned in a previous blog. Remember that the computer runs a number of times, very slightly altering the initial atmospheric conditions to see how that will change future projections. And the various computer models from across the world are telling us more or less the same story. That there is every chance of a blocked pattern of weather becoming established towards the end of next week, which could lead to bitter easterly winds and a risk of snow.

Below is an example of what the American operational model expects to happen from the latest midday run of the computer. It gives an idea of the type of pattern that may occur. Of interest are the coloured lines, called thickness lines, labelled 510 in deep blue. This depth of cold air has become quite rare across the UK in recent years.

This shows the expected temperatures at midday: Exceptionally cold across the whole of Europe.

At this stage, I have to sound a note of caution: None of this is set in stone and meteorologically we are a long way away from it becoming reality. But if this pattern does become established, then it could overall turn out to be the coldest winter since 1978/79 - a big departure from the run of very mild winters that we have grown accustomed to.

I will update this blog next week

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UPDATED SUN 24th JAN 1800

A milder interlude - but blink and you'll miss it

January looks likely to end as it began - with widespread frosts at night, and with a risk of snow showers mainly to coasts exposed to a strong northerly airstream with its origins in the Arctic.

High pressure will extend its influence from the East early next week, with a cold feel and a risk of frost and fog at night. Mid-week a warm front will extend from the Northwest, with temperatures becoming normal and possible above normal. But this will be very temporary, with cold Arctic air quickly following during the second half of the week. This will re-introduce widespread night frosts - with snow showers, mainly, but not exclusively to areas exposed to the north or northwest wind. The colder weather will last into next weekend. But there is some cheer as the coldest January (Based on CET) since 1987 draws to a close.

There should be lots of blue sky and sunshine too in this arctic northerly, quite a tonic after such a depressingly dull January.

ENDS

The intense cold air that affected us for the 4 week period from mid Dec to mid Jan is currently still over the near continent. Milder air has tried to re assert itself from the southwest this week, but has struggled to make inroads. So the UK is in the middle of a battle, and where the mild air from the southwest meets the cold continental air, there is always a risk of snow. Snow fell across parts of Wales and Southwest Britain yesterday, but the weather front bringing milder air was defeated by the cold air. The next one tonight will succeed, and as it does so the rain it brings could turn to snow for a time across the hills of Northern Britain.

What happens next is very finely balanced. Most operational models bring cold air back from the continent into eastern areas later in the weekend and into early next week. But what happens after that is very much open to question.

Each computer model runs a number of times, varying the initial starting conditions of the atmosphere very slightly to see what happens to the forecast. This is called ensemble forecasting. It gives us an indication of how likely, for example, a cold easterly is likely to last next week. The ensembles are telling us at the moment that only very small differences in the initial atmospheric conditions could result in very big changes to our weather next week. Some solutions bring mild air in from the northwest; others maintain and intensify the cold air from the east. In fact the ensembles are telling us that there is a 50/50 balance between those solutions having milder air winning by mid-week, and those which keep it cold.

We have already discussed the implications of El Nino Pacific warming in earlier blogs.

Our weather can be influenced in later Winter and early Spring by El Niño events in the Pacific. It's thought the warming of the stratosphere it brings has a knock on effect on the troposphere - the part of the atmosphere which is important to us - in causing the normal free flow of Atlantic weather systems from the west to stop, as higher pressure causes a 'block' in the atmosphere.

It was certainly an excellent indicator of the cold spell we had in December. But it is by no means a guarantee.

Throw into the mix Piers Corbyn's latest forecast from Weather Action, signalled weeks ago and re-iterated yesterday that next week will turn milder across the UK, due to the influence of solar magnetic particles on our atmosphere, then it's certainly going to be interesting to see which scenario wins. He also expects February to see a return to cold and at times wintry conditions.

Based on a cold and a mild scenario next week I have tried to estimate how cold January is likely to look at the end of the month, following December which was the coldest since 1996.

1) Cold weather winning next week:

It turns out that January would be the coldest, based on the Central England Temperature data set, since 1987, with a forecast CET of around 0.94C (compared to the January mean of 4.2C).

2) Milder weather winning next week:

The CET figure would be around 2.05C. This would still mean January would be the coldest since 1987.

So whichever outcome occurs, it would be in the top 50 coldest Januarys since CET records began 350 years ago

And for those that had it bad through the cold spell, spare a thought for those who had to suffer the horrendous winter of 1947. This nostalgic photograph was taken outside Keighley, West Yorkshire during early February 1947.

When confidence increases and I have a better idea as to which type of weather is likely to win next week I will update this blog accordingly

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It's been quite a week. Temperatures for the second time this winter in Yorkshire fell to -14C (7F), at Leeming in North Yorkshire on Thursday night. In Scotland -22C was recorded at Altnaharra in the Scottish highlands; and in Wales, the Met Office station in Trawscoed in Ceredigion recorded -14C while ice formed at the marina in Aberystwyth for the first time since the winter of1963.

Across the northern hemisphere extremes of cold have been reported, but It's important to point out that this pattern of weather is also leading to some areas of the world experiencing higher than normal temperatures too.

But what is causing it?

The main culprit is the little known Arctic pressure oscillation. It reversed sharply at the beginning of December and effectively shunted the jet stream much further south than normal, leaving us very much on the cold side of the jet, wide open to the influence of the Arctic and Russia.

So could we have forecast this severe cold spell of weather?

One long range forecaster I spoke to this autumn was convinced that this winter was going to be cold. His name is Joe Bastardi at Accuweather.com. Joe has a common sense approach to long range forecasting, an old fashioned style that has almost gone out of fashion in a meteorological world so dominated by powerful computers. He has an analytical mind second to none, and when I spoke to him he told me he was convinced that the weather patterns that we were having at the time reminded him of those which in the past had been followed by cold winters. He even went on to say that not only could this winter be cold across the USA and Europe, but it could be similar to those we used to experience in the 1970's. And this was way back in September.

Hindsight is a wonderful thing and I would be the first to admit that long range forecasting can be a mug's game. But there have been little clues along the way. Firstly, the North Atlantic oscillation (NAO) went negative during September. This in the past has been a good indicator of a colder, more anticyclonic winter in years gone by. The current El Niño in the Pacific also offers clues. El Niño's in the past have affected Europe's climate late in the winter and into spring. In particular February and March are often colder than average across Europe during Pacific El Niño events. Interestingly the American model has consistently forecast a colder than average February. (And The El Niño could give us a good warm summer but don't quote me on that!)

So why, at the same time that Joe Bastardi at Accuweather.com forecast a cold winter did the Met Office issue a forecast saying that this winter would be mild, with the chances of a cold winter less than 15%?

Clearly there is the rest of January and February to go, but such has been the intensity of the cold spell, which next week will run into its 4th week, then it would take something remarkable during the rest of winter for the Met Office's forecast to be right. It's also worth remembering that this comes off the back of the now infamous barbeque summer forecast, and lets not forget last winter, which the Met Office said again would be mild, but turned out to be the coldest for over 10 years.

The answer may well be quite straight forward. It's likely that the all powerful and dominant Hadley centre supercomputer predicted very little chance of a cold winter, just like it did last winter, and that, as they say, was that.

Which begs other, rather important questions. Could the model, seemingly with an inability to predict colder seasons, have developed a warm bias, after such a long period of milder than average years? Experts I have spoken to tell me that this certainly is possible with such computer models. And if this is the case, what are the implications for the Hadley centre's predictions for future global temperatures? Could they be affected by such a warm bias? If global temperatures were to fall in years to come would the computer model be capable of forecasting this?

If you have time, read again my article called 'Could the sun cast a shadow on global temperatures predictions' that I wrote before Christmas. In particular, read David Archibald's paper, peer reviewed in Energy and Environment journal, where he discusses the prolonged solar minimum we have been in, and what happened to CET temperatures (the longest temperature data set in the world) the last time we experienced such a solar cycle, and the implications for the weather across America and Europe.

Of course the fact that the severe winter has coincided with the very unusual solar cycle could easily be a coincidence, the winter just part of nature's natural variability if you like. Don't forget global warming predictions don't say that cold winters will never happen again, just that they will become less frequent in time. And there's no doubt about it we have been long overdue a prolonged cold winter.

At the very least, though, it's food for thought on this bitterly cold January weekend.

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The severe weather will be with us for some considerable time. Latest indications are that the next 10 days, taking us up to and through the middle of January, will remain bitterly cold with severe night frosts and further snow fall. Already depths in some areas are in excess of 30cms, with some northern Pennine areas now reporting 40 cms of snow, according to the Met office. Even the suburbs of Leeds have around 20 cms. These snow depths have not been seen since the winter of 1981/1982.

Of interest will be the strengthening easterly wind through Friday and the weekend and into next week. This will bring snow showers, frequent at times especially to eastern areas, with a risk of significant further accumulations. The drifting of lying snow will become a big problem. Already 10 feet drifts have been reported around villages close to Saddleworth moor.

So how does this rate with previous winters? It's already the longest cold spell since the winter of 1981/1982. It's impossible to make further comparisons with other winters because we are still only in the early part of January. But the most notable ones were 1978/79, 1962/63 and 1946/47.

1962/63 was the coldest of the last century. There was a lot of snow, but the dominant easterly weather pattern was also clear at times, which lead to very low overnight temperatures but sparkling Arctic type sunny days.

1946/47 was not statistically as cold, but much snowier and very grey. It was all in all a very miserable winter and because it was so soon after the second world war rationing was still in place, and such were the snow depths that some remote villages were cut off and close to starvation, unable to be reached from the outside.

So although the statistics tells us that 1962/63 was the coldest, people who lived through both winters will tell you that 1946/47 had much more impact and was far worse for a number of reasons.

Both winters had temporary milder interludes, but the cold air lasted through the winter and into March. When the thaw came, especially in 1947, widespread severe flooding followed.

Both winters were also dominated by strong easterly winds at times, and drifts were 15ft deep and more. Similar drifts are likely as we head through the weekend across higher parts of Yorkshire.

I'm on an outside broadcast in Stamford Bridge, East Yorkshire, this evening. I will add more as soon as I can free up some time, and will comment about how well this was predicted and possible explanations for the type of weather we are having.

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It's been the coldest December averaged across the UK since 1996. But here in Yorkshire it's been even colder than that at some sites. Leeming, in North Yorkshire, has had its coldest December since 1981 which is remarkable considering that during the first 10 days of the month we were still stuck in the mild and wet weather left over from November.

This week looks potentially disruptive with a high risk of some heavy snowfall. A weather front tonight will bring an awkward mix of freezing rain, sleet and snow from the north just in time for Tuesday mornings commute. Then the wind will swing round to the North or Northeast, and with deep cold air coming over a relatively mild North sea (although sea temperatures have fallen 3-4 degrees in the last 3 weeks) heavy snow showers are likely to form, and merge into longer spells of snow at times especially, but not exclusively, in eastern areas, with no let up expected in this type of weather even as we head into the weekend. Severe frosts are also expected at night, with daytime temperatures struggling to get above freezing point. Some places by Friday may have over a foot of snow.

And there is absolutely no sign of any change soon. More than 80% of weather models have a cold east or northerly type of weather lasting for the next 10-15 days. At the same time our usual wet and windy weather is way to the south, with the Jet stream lying somewhere through the Mediterranean. Hardly surprising that parts of southern Spain has had flooding not seen since the 1940's.

So it's looking increasingly like a winter the like of which we haven't seen for decades.

And this weather pattern is not unique to the UK and Europe. The NOAA satellite map below shows the extent of snow in the USA on Christmas day when a remarkable 63% of the country was covered in snow.

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