Untangling the global drivers of UK winter weather

25 11 2014

As we head towards the start of winter, which starts for meteorologists on 1 December, there’s always a great deal of media and public speculation about what weather we might have in store.

To answer that question, we need to look beyond the UK. The worlds’ weather is interconnected, and there are certain large scale global drivers which we know have influences on UK weather at this time of year – so what are these doing at the moment?

El Niño, which sees unusually warm sea surface temperatures across the tropical Pacific and can increase the risk of cold winter conditions in the UK, has been much discussed after initial signs of development earlier this year.

Its progress has been slow, however, and while there remains a good chance of a weak event by the end of the year it is also possible that El Niño conditions will remain neutral. In any case, this factor is not expected to be strong enough to exert much influence on weather patterns in Europe during the next three months.

The North Atlantic Oscillation (NAO) describes differences in the usual pressure patterns over the North Atlantic – with positive and negative phases.

A positive phase is thought more likely than a negative one on average over the next three months. This is characterised by enhancement of the westerly winds across the Atlantic which, during winter, brings above-average temperatures and rainfall to Western Europe.

As we head later into winter, confidence about the heightened likelihood of positive NAO reduces – suggesting chances of drier and colder conditions return closer to normal.

The Quasi-Biennial Oscillation (QBO) sees high level (stratospheric) winds over the equator change from westerly to easterly phases – and it’s currently in the latter of the two.

In winter months this can lead to a greater incidence of high pressure blocking patterns over the northern hemisphere, which would increase the probability of colder and drier weather across Europe. Essentially this is providing an opposite signal to the NAO.

There are other factors to consider too. For example, Arctic sea ice extent is slightly below average but as yet it is not clear whether this might have an impact on weather patterns in the UK.

No single one of these drivers will determine the UK’s winter on its own – instead they all interact together to govern the weather trends we can expect over the coming months.

Disentangling these different influences remains a challenging area of science which the Met Office is improving all the time, but detailed and highly certain UK outlooks are not possible over these timescales.

The Met Office’s long-range outlooks give probabilities based on scenarios of being considerably wetter or drier, colder or milder than usual.

Currently the outlook for December 2014 to February 2015 suggests that milder and wetter than average winter conditions are slightly more likely than other outcomes. However, compared to day-to-day weather forecasts, the probabilities are much more finely balanced – for example, the outlook gives a 1 in 4 chance of the mildest scenario and a 1 in 10 chance of the coldest scenario. These numbers suggest it would be a mistake to interpret the outlook for a very mild outcome as ‘highly likely’; likewise very cold conditions cannot be ruled out.

The outlook gives similar probabilities for precipitation (rain, hail, sleet and snow), with the chances of the wettest scenario being 1 in 4 and the chances of the driest around 1 in 10.

These three month outlooks cover a whole three month period, taking into account both day and night, as well as the whole of the UK. This means that even in the event of, say, an overall mild winter we could still see spells of cold or very cold weather.

With this in mind, what exactly we’ll see for the winter ahead remains uncertain. In terms of strong winds, heavy rainfall, cold snaps or even snow, while longer-range outlooks can give us general tendencies, the details can only be predicted by our day-to-day weather forecasts.

The Met Office’s accuracy over all timescales is world-leading, however, so you can trust that we’ll keep everyone up-to-date with all the latest information on the weather whatever the winter has in store.





Wet wet wet this winter?

17 11 2014

Every year there’s a huge amount of media speculation about what weather we’ll see during winter, and this year is no different.

After a recent slew of stories claiming we’re in for the coldest winter on record (which weren’t based on information from the Met Office), there are now stories claiming we’re forecasting the wettest winter in 30 years.

That’s not the case and appears to be a misunderstanding of our three-month outlook for contingency planners.

First of all, last winter was the wettest in our digital records dating back to 1910, so if we were to have a wetter winter than that it would be the wettest in over a century – not just for 30 years.

But that’s not what our contingency planners outlook says. As we’ve pointed out here many times in the past, this product isn’t like our short range forecasts – it doesn’t tell you definitively what the weather is going to be and that’s why it’s not really that useful for the public.

What it does do is make an assessment of the likelihood of seeing wetter or drier than average, and milder or colder than average conditions for the whole of the UK for the whole three month period.

Recent outlooks have been signalling increased risk of milder and wetter conditions for the past couple of months, and indeed that’s what we have seen through October and the start of November. So the most likely predicted outcome is what actually happened for these months – but that won’t always be the case.

While the recent three month outlooks also highlighted the risk of more unsettled than average conditions, this does not give specific details or tell us whether any records will be broken.

For detailed weather forecasts, our five-day forecasts and weather outlooks to 30-days give the best and most up-to-date advice.





The Met Office’s outlook to the end of 2014

5 10 2014

There are some headlines in the media today which suggest the UK faces another mild, wet and stormy winter this year based on the latest Met Office three month outlook for contingency planners.

Every month the Met Office updates its three month outlook for contingency planners, which is available for anyone to view on our website.

However, it’s not like a normal weather forecast. It’s an experimental and complex outlook based on probabilities which is designed specifically for those who plan ahead for various contingencies based on possible likelihoods.

As we’ve discussed previously, the outlook assesses the likelihood of five different scenarios for both temperature and rainfall for the whole of the UK for the whole three months, based on the most probable prevailing weather patterns.

It’s a bit like the science-equivalent of factoring the odds on a horse race and like any horse race, it’s always possible the favourite won’t win.

This is why the outlook has to be used in the right context. So it’s useful for contingency planners, but not that useful for the public who want to know when we might see unsettled weather or which weekend looks good for an outdoor event.

What does the current outlook say?

Our latest three-month outlook suggests an increased risk of milder and wetter than average conditions for the period Oct-Nov-Dec based on our seasonal forecasts and those from other leading centres around the world.

However, there are still substantial probabilities that average or opposite (ie cool and/or dry) conditions may occur. This is because there are many competing factors that determine what our weather will be like in the coming months.

The outlook also highlights an increased risk of unsettled weather relative to what is usual for the time of year, but – again – there are still reasonable chances of other scenarios.

The increased risk of more unsettled than average conditions does not mean the late autumn and early winter will necessarily be like that of last year.

Some more context on the outlook

 

The outlook suggests that the risk of our weather coming in from the Atlantic, which brings unsettled conditions, increases from mid-October through November and December.

This is a fairly typical set up for the time of year, when we do expect unsettled weather, but the outlook does suggest the risk of more unsettled than normal conditions.

As the outlook covers the transition from autumn into the start of winter, there will be big changes in how UK weather is influenced by prevailing weather patterns during the period.

The current settled conditions bring us generally warm weather in early autumn, but the same weather pattern in winter would likely bring cold weather in from the rapidly cooling continent.





The Met Office’s outlook for UK winter 2013-14

21 02 2014

There are some headlines in the media today discussing the Met Office long range forecast for this winter.

Firstly it’s important to remember that it’s our short and medium term forecasts that are relied on by emergency responders to help them manage the impacts of severe weather.

The Met Office’s five-day forecasts and severe weather warnings have provided excellent guidance throughout the period of exceptionally stormy and wet weather we have experienced this winter. This advice has helped everyone from the emergency services, to government organisations and the public plan ahead for the conditions we’ve seen.

The news stories are based on information taken from our three month outlook for contingency planners, issued at the end of November 2013 so, what can our three month outlooks tell us?

These outlooks are not like our other forecasts because, as we have discussed previously, it’s not currently scientifically possible to provide a detailed forecast over these long timescales.

Instead, the outlook assesses the level of risk connected to five different scenarios for both temperature and rain/snowfall for the UK as a whole; they do not mention specific areas such as the West Country or the Somerset Levels. It’s a bit like the science-equivalent of factoring the odds on a horse race.

However, as with any horse race, it’s always possible that the favourite won’t win – so these probability scenarios have to be used in the right context. This is why they’re useful for contingency planners who plan ahead based on risk, but not that useful for the general public.





Winter so far – 18th February rainfall update

18 02 2014

As the UK heads into a period of more normal unsettled winter weather weather, the Met Office’s National Climate Information Centre has looked at statistics for this winter so far (from 1 December 2013 to 13 February 2014).

These add to previous facts and figures we put out earlier this month, and show a picture of continuing exceptional rainfall across many areas.

Looking at regions around the UK, these provisional figures show the region of central southern and southeast England has already exceeded its record winter rainfall in the series back to 1910. Rainfall here currently at 459.3mm*, 22mm above the previous record of 437.1mm set in 1915 with two weeks still to go to the end of the season. This winter also currently ranks as the 4th wettest winter (if there is no further rain) for southwest England and south Wales combined and the 3rd wettest for England South.

Both the UK as a whole and Wales are fairly close to exceeding their respective record wettest winter levels in the national series dating back to 1910 (see table below). Average rainfall for the rest of the month could see those records broken.

All countries across the UK have already exceeded their typical average rainfall for the whole winter (according to the 1981-2010 long-term averages). Normally at this stage of the season, you’d expect to have seen only around 80% of that whole season average.

All areas are also on target for a significantly wetter than average winter, with typically around 130-160% of normal rainfall if we get average rainfall for the rest of February.

All countries and areas are also on target for a warmer than average winter.

Current record wettest winters:

Country Year Rainfall Winter 2014 to date*
UK 1995 485.1mm 452.6mm
ENGLAND 1915 392.7mm 345.6mm
WALES 1995 684.1mm 645.1mm
SCOTLAND 1995 649.5mm 590.4mm
NORTHERN IRELAND 1994 489.7mm 386.2mm

*These are provisional figures from 1 December 2013 to 13 February 2014 and could change after final quality control checks on data.





Statistics for winter so far

11 02 2014

As the unsettled UK weather continues this week, the Met Office’s National Climate Information Centre have looked at statistics for this winter so far (from 1 December to 10 February).

These add to previous facts and figures we put out earlier this week, and show a picture of continuing exceptional rainfall across many areas.

Looking at regions around the UK, these provisional figures suggest the region of SE and Central S England has already exceeded its record winter rainfall in the series back to 1910. It is currently at 439.2mm*, less than 2mm above the previous record set in 1915 with 437.1mm of rain.

For the UK as a whole, and also for Wales, both are fairly close to their respective record wettest winter levels in the national series dating back to 1910. Average rainfall for the rest of the month would likely see those records broken.

All countries across the UK have already exceeded their typical average rainfall for the whole winter (according to the 1981-2010 long-term averages). Normally at this stage of the season, you’d expect to have seen only around 80% of that whole season average.

All areas are also on target for a significantly wetter than average winter, with typically around 130-160% of normal rainfall if we get average rainfall for the rest of February.

All countries and areas are also on target for a warmer than average winter.

Current record wettest winters:

Country Year Rainfall Winter 2014 to date*
UK 1995 485.1mm 429.2mm
ENGLAND 1915 392.7mm 328.0mm
WALES 1995 684.1mm 618.7mm
SCOTLAND 1995 649.5mm 558.5mm
NORTHERN IRELAND 1994 489.7mm 360.0mm

 

*These are provisional figures from 1 December 2013 to 10 February 2014 and could change after final quality control checks on data.





Mild wet winter continues in early January figures

16 01 2014

Provisional half-month statistics up to the 15th of January show a continuation of the generally mild and wet theme of the UK’s winter thus far.

The mean UK temperature up to the 15th of January is 5.1 °C, which is 1.5 °C above the long-term (1981-2010) average.

The mild January so far follows on from a mild UK December, which had a mean temperature of 5.7 °C, which is 1.8 °C above the long-term average – making it the eighth mildest December in records dating back to 1910, and the mildest since 1988.

It’s a similar story with UK rainfall. We’d normally expect about 48% of the January average rainfall by the 15th of the month, but the UK has seen 87.9mm so far – which equates to 72% of the January average.

As usual, there are regional varations. England has been particularly wet so far this month, having already seen close to its full-month average, and Wales is not too far behind. Scotland and Northern Ireland, however, are closer to the ‘normal’ amount of rain we’d expect at this stage.

The wet January so far once again follows the theme set in December, which saw 184.7mm of rain – which is 154% of the average for the month.

While this means January, and winter, so far have been mild and wet, it doesn’t mean they will finish that way. We often see half-month or half-season figures which then change dramatically by the end of the period. So the message is, it’s too early to judge how January 2014 or winter 2013/4 will finish up.

The main reason for the mild and wet weather so far is that we have seen a predominance of west and south-west winds, bringing in mild air from the Atlantic – as well as generally unsettled conditions.

The table below shows provisional figures from 1-15 of January, with actual figures so far compared to full-month averages. We would normally expect rainfall and sunshine to be about 48% of the full-month average at this stage.

Mean Temperature Sunshine hours Rainfall  
January 1-15
Actual Diff from Avg Actual % of Avg Actual % of Avg
  degC degC hours % mm %
UK 5.1 1.5 26.1 55 87.9 72
England 6.0 1.9 34.7 64 80.4 97
Wales 5.8 1.7 20.6 42 137.7 88
Scotland 3.6 1.0 15.4 43 91.2 51
N Ireland 4.4 0.2 14.6 33 62.8 54




UPDATED: Wind and rainfall data 4 to 5 December 2013

5 12 2013

UPDATED TO INCLUDE LATEST WIND SPEEDS AS AT 3PM, 5 DECEMBER 2013

As forecast, there have been severe gales with widespread gusts of between 60 and 80mph across Scotland and northern parts of England. Some very high level mountain sites have reported speeds of over 140mph, but these are in very exposed areas and not representative of the winds most people have experienced.

UK MAX HOURLY GUST SPEED 4 DEC 1800HRS – 5 DEC 0600HRS
SITE NAME AREA ELEVATION MAX GUST SPEED (MPH)
ALTNAHARRA SUTHERLAND 81 93
LOCH GLASCARNOCH ROSS & CROMARTY 269 92
DRUMALBIN LANARKSHIRE 245 90
SOUTH UIST RANGE WESTERN ISLES 4 89
HIGH BRADFIELD SOUTH YORKSHIRE 395 87
EMLEY MOOR WEST YORKSHIRE 267 86
STORNOWAY AIRPORT WESTERN ISLES 15 85
ORLOCK HEAD DOWN 35 84
KINLOSS MORAY 5 83
SPADEADAM CUMBRIA 285 83
ESKDALEMUIR DUMFRIESSHIRE 236 83
SKYE: LUSA WESTERN ISLES 18 83
TIREE ARGYLL 9 82
DUNSTAFFNAGE ARGYLL 3 82
 MOUNTAIN SITES MAX GUST SPEED 4 DEC 1800HRS – 5 DEC 0600HRS
SITE NAME AREA ELEVATION MAX GUST SPEED (MPH)
AONACH MOR INVERNESS-SHIRE 1130 142
CAIRNWELL ABERDEENSHIRE 928 137
BEALACH NA BA ROSS & CROMARTY 773 116
GREAT DUN FELL CUMBRIA 847 113
GLEN OGLE PERTHSHIRE 564 106

It has been very wet in some areas overnight as well with 50.8mm of rain being recorded at Tyndrum, Perthshire and 42.4mm at Cluanie Inn, Ross & Cromarty.





The Met Office’s outlook for UK winter

29 11 2013

There are some headlines in the media today which suggest the Met Office is warning of exceptionally cold weather for three months.

However, the Met Office hasn’t issued a warning along these lines and we have not highlighted months of ‘exceptionally cold’ weather ahead. If there is any sign of significantly cold weather or disruptive snow in the forecast, we will keep the country up to date through our forecasts and warnings.

The news stories are based on information taken from our three month outlook for contingency planners, so let’s take a closer look at that.

What does our three month outlook say?

This outlook is not like our other forecasts because, as we have discussed previously, it’s not currently scientifically possible to provide a detailed forecast over these long timescales.

Instead, the outlook assesses the level of risk connected to five different scenarios for both temperature and rain/snowfall. It’s a bit like the science-equivalent of factoring the odds on a horse race.

The current outlook for December-January-February says the chance of the coldest scenario happening is between 20 and 25% and the chances that the period will fall into the warmest scenario is between 10 and 15%.

So while uncertainty is quite large, below average temperatures are more likely than above average (for note, average maximum temperatures for the UK in winter are about 6.6C and average minimum temps are about 0.9C).

However, as with any horse race, it’s always possible that the favourite won’t win – so these probability scenarios have to be used in the right context. This is why they’re useful for contingency planners who plan ahead based on risk, but not that useful for the general public.

So what will winter be like?

Obviously there’s always a lot of interest to know what winter will be like – how cold will it be, how much snow will we get and where and when will it fall?

The Met Office is working with research partners around the world to improve longer range forecasting, but it’s not currently possible to forecast snow or exact temperatures three months ahead.

However, our 30-day outlook (under the text forecast tab) provides a look ahead to the general type of weather we’re likely to see in the UK.

Currently it says that after today, we’ll see settled weather and fairly normal temperatures into the first week of December before the chance of some colder, more changeable weather towards the end of next week. This may last a few days before giving way to milder and unsettled weather.

For the mid to latter part of December, there are indications that temperatures are likely to remain near or slightly below average for the time of year, but otherwise fairly normal conditions for early winter are most likely.

With regards to forecasting snow, because there are so many factors involved, generally that can only be discussed in any detail in our five day forecasts.

If there is any sign of significantly cold weather or disruptive snow in the forecast, we will keep the country up to date through our forecasts and warnings.





Winter Forecasting – Responding to the headlines

12 10 2013

Once again it is the season for speculation and big headlines regarding what the weather will do over the winter period. The front page of the Daily Express today claims: ‘Worst winter for decades: Record-breaking snow predicted for November’.

We saw similar headlines last year and instead winter 12/13 ended up being only the 43rd coldest on record with an average temperature of 3.3C and flooding until the turn of the year.

What the Daily Express has failed to explain to its readers is that there is absolutely no certainty about what weather the UK will see over the winter period. The science simply does not exist to make detailed, long-term forecasts for temperature and snowfall even for the end of November, let alone for the winter period, which does not officially start until 1 December.

While we have seen a return to more normal, cooler temperatures for this time of year, this is no indication of what we can expect over the next four months with regards to temperatures and when we might see snow. It is far too early to tell.

Ultimately, we’re heading into winter and it is perfectly possible that we will see the whole range of weather that we get in winter at some point over the coming months, including snow and freezing temperatures, but also heavy rain, windy weather and mild conditions too.

Our five day forecasts and warnings will provide you with the best possible guidance on any periods of cold weather, frost or the likelihood of snow, giving detailed local information across the UK to help you make the most of the weather over the coming months.








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