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.





Severe weather to affect western France

12 08 2014

A spell of severe weather is expected to affect parts of France overnight and through Wednesday morning as an area of low pressure makes its way in from the Bay of Biscay.

The  area of low pressure highlighted in the satellite image above is expected to deepen and develop before affecting parts of France this evening and overnight.

Pressure chart for 1 am Wednesday 13 August

Pressure chart for 1 am Wednesday 13 August

Forecast rainfall for 1 am Wednesday 13 August

Forecast rainfall for 1 am Wednesday 13 August

 

 

 

This brings the risk of severe thunderstorms across western, then southern France overnight and during Wednesday morning. This will bring the potential for flash flooding and will give squally winds, with disruption to local infrastructure and to holiday makers in the region. Very strong winds and high seas are also likely for a time overnight along the western coastline of France. Meteo France currently has severe weather warnings in force.

 

This area of wind and rain should then move quickly across Switzerland and southern Germany during Wednesday afternoon.





Rain over the Bank Holiday Weekend, with more to come

27 05 2014

The Bank Holiday weekend saw a good deal of dry and bright weather in places, but there was also heavy rainfall in some spots over the three days with some significant rainfall totals.

Much of England and Wales had a wet Saturday as rain pushed northwestwards with heavy, and thundery showers following.

Sunday brought heavy showery rain to western and northern parts of the UK, with 25 mm of rain falling in three hours around the Edinburgh area.

Heavy rain pushed in from the southeast on Bank Holiday Monday, whilst to the west and north of this there was some sunny weather, but also heavy and thundery showers for Cornwall, Northern Ireland and Scotland.

Here are the highest UK rainfall totals for each of the three days of the Bank Holiday:

 

Rainfall totals from 0900 Saturday 24 May – 0900 Sunday 25 May
Site Area Amount (mm)
Liscombe Somerset 32.2
Usk Monmouthshire 29.0
Tredegar Gwent 23.4
Okehampton Devon 22.5
Waddington Lincolnshire 22.0
Sheffield South Yorkshire 22.0

 

Rainfall totals from 0900 Sunday 25 May – 0900 Monday 26 May
Site Area Amount (mm)
Edinburgh, Gogarbank Midlothian 26.2
Cardinham Cornwall 17.8
Edinburgh, Royal Botanic Garden Midlothian 17.4
Tyndrum Perthshire 17.2
Camborne Cornwall 14.2

 

Rainfall totals from 0900 Monday 26 May – 0900 Tuesday 27 May
Site Area Amount (mm)
Wattisham Suffolk 31.2
Brooms Barn Suffolk 25.4
Cavendish Suffolk 21.8
Charsfield Suffolk 19.2
Cambridge Cambridgeshire 17.0

 

Looking ahead through the rest of this week there is more rain to come, particularly for eastern and northeastern England, while Scotland (especially the north) has the best of the warm, sunny weather.

Suffolk has already seen heavy rainfall through Tuesday morning with over 30 mm of rainfall at Wattisham through the first 9 hours of the day.

This is going to push northwards through Tuesday into Norfolk and Lincolnshire. A Met Office yellow warning has been issued to warn of rainfall amounts reaching around 30mm in some spots which could lead to some localised flooding.

There are also going to be some heavy showers over southern parts of Wales and parts of the West Country.

Wednesday will again be wet for many, especially around northeast England with parts of Yorkshire at risk of over 30 mm, for which another yellow rainfall warning has been issued. With strengthening winds this will make it feel quite unpleasant at times.

More showers or longer spells of rain are expected for Thursday, before things should turn generally drier, brighter and warmer by the weekend.





Spring has sprung

5 03 2014

Warmer, drier weather is on the way for parts of the country.  As we move through the week a north–south divide develops across the UK with Scotland, Northern Ireland, northern England and parts of Wales being changeable and windy. However in the south high pressure will dominate  bringing dry weather for the weekend, with the best of the weather in the Southeast.

Temperatures are expected to reach mid to high teens in the South this weekend (8th – 9th March), while northwest England and Scotland are likely to see spells of strong winds and rain and there is a risk of overnight frosts.

This is in sharp contrast to the record breaking winter we have just experienced.  It was the wettest winter for the UK, England, Wales and Scotland, and the second wettest winter for Northern Ireland in the record series dating from 1910. It was the stormiest UK weather for 20 years with at least 12 major winter storms affecting the UK in two spells from mid-December to early January, and again from late January to mid-February.

For a time early next week the temperatures are expected to return to nearer normal, or slightly above, the average for the time of year (9 °C).  High pressure is again expected to dominate through next week leaving largely settled conditions it should continue to feel “spring like” with some sunshine around and light winds.

When does Spring start?

Meteorologically speaking spring stretches from 1 March to the end of May. Astronomically, spring typically starts on the day of spring equinox, around the 20 March in the Northern Hemisphere.

Weather in spring is often calm and dry with temperatures rising in the day but staying cool at night.





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.





Major Atlantic storm – wind speeds and rainfall totals

28 10 2013

The Atlantic storm which has caused disruption across parts of England and Wales this morning has now moved off into the North Sea.

We expect the most powerful winds and heavy rain associated with the storm to clear eastern areas in the next few hours, after which most parts of the UK will see a bright and breezy day with occasionally heavy, blustery showers.

The storm developed as expected just off to the south west of the UK last night, before tracking up into the Bristol Channel in the early hours of the morning.

It then tracked across the Midlands, moving off into the North Sea just to the north of East Anglia later in the morning. As the storm moved across, it brought exceptionally strong winds and heavy rain with it – causing widespread impacts.

Now the storm has cleared through, we are expecting typically unsettled autumn weather over the next couple of days – with some bright spells, mixed in with showers or longer periods of rain and breezy conditions.

This video shows the storm as it crossed the UK:

Below are some of the strongest recorded winds and heaviest total rainfall amounts:

Maximum gusts during the storm:

STATION NAME AREA MAX GUST (MPH)
WIGHT: NEEDLES ISLE OF WIGHT 99
LANGDON BAY KENT 82
ISLE OF PORTLAND DORSET 81
ANDREWSFIELD ESSEX 79
ODIHAM HAMPSHIRE 78
THORNEY ISLAND WEST SUSSEX 76
SOLENT HAMPSHIRE 75
WIGHT: ST CATHERINES POINT ISLE OF WIGHT 75
YEOVILTON SOMERSET 75
LYNEHAM WILTSHIRE 75
HURN DORSET 74
MANSTON KENT 70
HEATHROW GREATER LONDON 69

Highest rainfall totals from 6pm on 27 October 2013 to 8am on 28 October 2013:

STATION NAME AREA RAINFALL TOTAL (MM)
OTTERBOURNE W WKS HAMPSHIRE 50
WYCH CROSS EAST SUSSEX 45.4
CARDIFF, BUTE PARK SOUTH GLAMORGAN 44.8
HURN DORSET 42
WIGGONHOLT WEST SUSSEX 37.2
ST ATHAN SOUTH GLAMORGAN 37
ODIHAM HAMPSHIRE 35
WELLESBOURNE WARWICKSHIRE 34.8
ALICE HOLT LODGE HAMPSHIRE 34.4
LISCOMBE SOMERSET 34.4




Cyclones set to strike India and the Philippines

11 10 2013

While the tropical storm and cyclone season for the northern hemisphere has been relatively quiet this year, the last few weeks has seen a spike in activity with three tropical cyclones currently active.

The north Indian Ocean sees tropical storms develop during two periods of the year – April to June and October to December.

Cyclone Phailin at 0455 UTC 11 October 2013. Image from the NASA Terra satellite.

Cyclone Phailin at 0455 UTC 11 October 2013. Image from the NASA Terra satellite.

Cyclone Phailin formed in the Bay of Bengal earlier this week and has become the most intense cyclone in this region since Cyclone Sidr in 2007. At the time of writing it has 1-minute average sustained winds of near 155 mph.

Phailin, which is a Thai word for ‘sapphire’, is expected to make landfall over the Odisha state of India on Saturday night and bring destruction from its strong winds, heavy rain and storm surge.

It is likely to be the strongest cyclone to hit India since the devastating ‘Odisha Cyclone’ of 1999, and it is possible it could be even stronger.

Meanwhile Typhoon Nari is continuing a busy spell for tropical storms in the last few weeks in the west Pacific Ocean.

With winds near 100 mph, Nari is making landfall over the northern Philippines today before moving into the South China Sea where it could continue towards a second landfall in China or Vietnam.

Behind Nari, another storm is developing called Wipha. This is set to strengthen into a typhoon and move northwards in the direction of Japan.

Landfall over Japan is possible, but at this stage a glancing blow to southern coastal regions of the country in the middle of next week is the most likely outcome.

Official warnings of west Pacific tropical storms are produced by the Japanese Meteological Agency (JMA). Official forecasts of Indian Ocean tropical storms are provided by the Indian Meteorological Department.

For more information on tropical cyclones worldwide, visit our web pages or follow @metofficestorms on Twitter.





Forecasting challenges this weekend

14 06 2013

Nick Grahame, Chief Forecaster at the Met Office, talks us through the forecasting challenges this weekend.

Sometimes the atmosphere can provide a real challenge for forecasters even in the shorter range. Take for example this weekend – there’s a low pressure system over the west Atlantic and, on the face of it, appears to be heading our way. However, as it approaches our shores on Saturday night, forecast models are suggesting a large degree of uncertainty in terms of where it goes next. Some continue to bring it towards the southwest on Sunday, which would result in a rather miserable day for many southern areas. The other scenario though is for the low pressure system to stall and stay well away from us. If that happened then southern areas would stay fine and bright. In these situations, it is really important for forecasters and broadcasters to find a meaningful way to talk about the most likely outcome but then to also express the uncertainty. This is important for those who are planning events etc (it is Fathers Day on Sunday of course).

So why is there so much uncertainty?

Over the weekend, we are going to see some very complex patterns developing over the Atlantic which will ultimately determine where the low will track. For those who like technical speak, it’s called a trough disruption and forecasting this phenomenon continues to be a major challenge to both computer models and humans alike. So the best thing to do is keep up to date with the forecast to get the latest on how things are expected to develop over this weekend.





Never mind the stories, summer is not over yet

13 06 2013

After a fortnight of settled and fine weather for most parts of the UK, we’re now seeing more changeable conditions which have led to stories claiming summer is ‘over before it even began’.

They point to our 30-day outlook, which it’s fair to say does make reference to changeable conditions being likely to persist through into the start of July.

However, before we all write off summer, it’s important to emphasise a couple of points.

Firstly, changeable weather isn’t all bad. In this case it means we’re likely to see mainly westerly winds which will allow weather systems to push in from the Atlantic, bringing spells of rain at times. But we’ll also see some dry and bright or sunny spells at times too. So it’s what you’d term as typically British weather and far from a ‘wash out’.

Secondly, we’re not even half way through June. Now, for us meteorologists, the summer runs until the end of August. That means even the 30 day outlook does not get us to half way through the season – so there is still plenty to play for in the forecast for summer 2013.

It’s also worth pointing out that so far, summer has been pretty good – since it began on 1 June, somewhere in the UK has seen a temperature of 20C or above every day.








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