Rainfall on UK’s wettest day on record could have more than filled Loch Ness

Saturday 3 October 2020 is now the wettest day on record since 1891 for UK-wide rainfall. It received the greatest rainfall in any single day averaged out across the UK, beating the previous record on the 25 August 1986.

UK rainfall map 3 October 2020

Saturday 3 October was the wettest day in the UK rainfall record stretching back to 1891.

Dr Mark McCarthy is the head of the Met Office National Climate Information Centre. He said: “In climate statistics, 2019 will be remembered for possessing the UK’s hottest day, whereas 2020 will be associated with rainfall records. Saturday 3 October – the day which followed Storm Alex – currently holds the record for the UK’s wettest day in a daily series stretching back to 1891 – that’s over 47,000 days. The rainfall was very widespread resulting in average rainfall across the entire UK of 31.7mm, or to put it another way, if expressed as the volume of rain that is more than the capacity of Loch Ness – the largest lake in the UK by volume at 7.4 cubic kilometres of water. It is exceptional to have 30 to 50mm or more of rain falling so extensively across the UK – from the south coast of England to the north coast of Scotland – in a single day”. The previous record was 29.8mm on 25 August 1986.

Loch Ness

At 7.4 cubic kilometres, Loch Ness is the largest lake in the United Kingdom by volume. Pic: Shutterstock.

 

 

Generally, the start to October (1-13th) has been very wet with the early provisional statistics showing the UK overall has seen 68% of its average rainfall for the month of October and England has been the wettest with 87% of its monthly average, in particular south east and central southern England already reaching 110%.

Commenting on 2020 Dr McCarthy added: “Remarkably, 2020 also has the UK’s third wettest day on 15th February with 27.2mm, from named storm Dennis during what then became the wettest February on record”.

More than 20 counties across the UK have already had 100% or more than their average October rainfall and many others are not far behind. Oxfordshire has been the wettest county compared to the 1981 – 2010 average with 148% average rainfall (107.1mm). Followed by Buckinghamshire reaching 139% (103.4mm) of its average rainfall, Berkshire with 138% (108.0mm) and Hertfordshire reaching 132% (96.9mm). Other counties already reaching 100% or above are Aberdeenshire, Angus, Banffshire, Bedfordshire, Berwickshire, Cheshire, City of London, City of Aberdeen, East Lothian, Essex, Gloucestershire, Greater London, Hampshire, Isle of Wight, Kincardineshire, Moray, Northamptonshire, Staffordshire, Surrey, Tyne and Wear, Warwickshire, Wiltshire and Worcestershire.

Wales, Scotland and Northern Ireland rainfall statistics remain at average numbers, and conversely Argyll and Bute has been significantly drier with only 29% of its average rainfall (70.7mm). The distribution of rainfall can be seen in the map below.

Average rainfall for October 2020

Already during October, many parts of the UK have recorded more than their monthly average rainfall for the month.

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Climate projections show extreme UK’s weather will become even more extreme

“The UK’s set of climate projections are the best window we have on how climate change is likely to affect us out to the end of the century,” said Professor Jason Lowe OBE*, the lead for UKCP – the UK’s climate projections.

The latest iteration of climate projections for the UK were released in 2018, updating the set from 2009. In the early days of climate projections, users were able to examine features such as the expected rise in average temperature for a given location at a particular time of year. “But users also need an understanding of what extremes of weather will be like: What will be the maximum temperature in summer? Or how much rain will fall in the heaviest rainfall events,” added Professor Lowe. Being able to interrogate the data in this way is exceedingly important for a whole range of user groups, from the rail industry to water companies and from town planners to the energy sector.

In 2019 there was a programme of additions , including a rollout of a new set of projections which examine climate extremes on a grid of 2.2km. This provides new capability to resolve the fine detail of weather extremes and predict events such as flash flooding, based on new capability to resolve the dynamics of thunderstorms.

In addition to more local detail, information is needed on uncertainties associated with future extremes, in order to support assessments of risks at the city-scale, for example. Later this week the Met Office will be releasing a further update which will add new probabilistic projections on the hottest and wettest weather extremes. Dr Simon Brown, who led this extension, explains: “This work provides a range of plausible outcomes for rare events expected on average once every 20, 50 and 100 years, for a range of emissions scenarios. This will allow planners to weigh the risk of different outcomes against the costs of adaptation.”

Exeter temperature extremes

One -in-twenty year temperature extremes for Exeter. Black line is the median value.

Ahead of the release of the data for the whole of the UK, the Met Office has released information for Exeter which shows the impact that climate change could be expected to have on the city.

Currently, in Exeter there is around a one-in-twenty chance of the city recording daily maximum temperatures exceeding 33.0 C, in a given summer. However the figures show that even with a mid-range scenario of greenhouse gas emissions (RCP4.5), this value would be more likely than not to exceed 35.0 C by 2090, while maximum temperatures of over 40.0 C cannot be completely ruled out.

The figures for rainfall extremes are also higher in the future than now. Currently, there is a likelihood that in one winter out of twenty the city will see a single day with over 45mm of rainfall, but by 2090 the same figure is nearly 50mm; around a 10 per cent increase of rainfall on the heaviest day for rain in winter. The projections show that values of around 60mm cannot be ruled out completely.

Professor Jason Lowe

Professor Jason Lowe OBE

More information about UKCP is available on the Met Office’s Weather Snap podcast.

 

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How will La Nina affect our winter weather?

La Niña is now present in the tropical Pacific and forecasters are suggesting these conditions will continue throughout the winter months.  

La Niña is one of the three phases of the phenomenon known as the El Niño-Southern Oscillation, El Niño – the warm phase, La Niña – the cool phase and lastly the neutral phase. During La Niña strong trade winds blow warm water towards the west Pacific causing an upwelling of cool water from the ocean depths in the east Pacific leading to variations in global weather. 

These changes in the location of warm and cool ocean water lead to a shift in rainfall towards the western Pacific putting areas such as north-east Australia, and Indonesia at risk of heavier than normal rainfall. While areas on the other side of the tropical Pacific, such as California, could be at risk of drought. La Niña can even influence the Atlantic jet stream and our weather here in the UK.  

Prof. Adam Scaife, head of long range prediction at the Met Office said, “La Niña has a profound effect on weather across the globe with us even seeing impacts that extend across the UK.  

“In late autumn and early winter it historically promotes high pressure in the mid-Atlantic, which stops Atlantic weather systems from delivering mild air to the UK, and therefore can allow cold conditions to intensify. However, in late winter La Niña can drive a shift of the jet stream towards the Poles increasing storminess and heavy rainfall, while bringing milder conditions”.  

Other factors affecting our winter weather.  

The Quasi-Biennial oscillation, the variation in winds high above the equator, is in its westerly phase at present and this increases the chance of a mild, wet and stormy winter. 

Meanwhile, the sun is in a new solar weather cycle, solar cycle 25. This cycle started around 9 months ago and at this stage can be associated with colder winter weather.  

How will La Niña impact global temperatures? 

Globally 2020 remains on track to be one of the warmest on record. Although La Niña historically reduces global temperatures, it is not expected to be enough to counterbalance human-induced climate change, but it may be enough to just prevent 2020 from being a new record. 

This comes after 2019 was one of the three hottest years on record and all the years since 2013 have been warmer than any previous years since records began in the 1800s. 

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Weather Statistics for September

Looking back at September as a whole it turned out to be a fairly average month, although there were a few notable events. For the first time in 4 years we saw temperatures reach 30 degrees and a few long running observing sites recorded their highest September temperature on record, although the end of the month saw more unsettled weather and cooler air, including a record low September temperature for Northern Ireland.

The first few days of September were rather unsettled, with frontal systems moving across from the west. Southern areas began to see less in the way of rain from the 9th onwards, whereas fronts continued to affect the north, with an especially wet period in western Scotland on the 12th/13th. Warm air moved into southern and eastern areas from the 14th, with a late-season hot spell bringing temperatures not far off 30°C on the 14th and peaking at 31.3°C on the 15th, and settled conditions continuing beyond that for another few days. However, around the 23rd the weather became more unsettled and decidedly cooler.

Rainfall

September rainfall was well below average for most regions of the UK, with only parts of western Scotland and East Anglia bucking this trend. Argyll and Bute received 203mm of rainfall, thanks mainly to heavy rain on the 12th while a slow-moving band of rain sat over much of the East Anglian coast on the 25th boosting rainfall levels here. Over the month Norfolk recorded 93.7mm of rain, 66% above its September average, with Houghton Hall receiving 45.2mm of rainfall on the 25th alone, while Cambridge weather station, around 55 miles inland, recorded no rainfall at all on that day.

Rainfall
Provisional September figuresActual rainfall% of the September average   
UK74.3mm77
England44.9mm65
Wales76.2mm65
Scotland121.8mm90
Northern Ireland58.1mm85

Temperature

For the first time since 2016 we saw temperatures reach 30 degrees in September. The 14th and 15th September were the warmest days this month. The 14th reached 29C and 6 weather stations recorded temperatures of 30C or above on the 15th.

Back in 2016 the hot weather was longer lasting and more wide-spread with temperatures reaching 34.4C at Gravesend in Kent on 13th September 2016.

Northern Ireland recorded its lowest minimum temperature on record for September on the 27th with a minimum of -3.7C. This beats the previous record of -3.6C which was again set at Katesbridge in 2018.

Maximum temperature  Minimum temperature 
Provisional September figuresActual °CDifference from Sept average °CActual °CDifference from Sept average °C
UK17.10.68.6-0.2
England18.60.79.3-0.2
Wales17.20.68.9-0.2
Scotland14.80.47.3-0.3
Northern Ireland16.50.48.6-0.1

Sunshine

September was a sunny month overall for many with most areas seeing above average sunshine hours.

Sunshine
Provisional September figuresActual sunshine in hours% of the September average   
UK145.3117
England166.2121
Wales153.7120
Scotland112.5107
Northern Ireland121.9107

You can get the most accurate and up to date forecast for your area using our forecast pages and by following us on Twitter and Facebook, as well as using our mobile app which is available for iPhone from the App store and for Android from the Google Play store. You can check the latest weather warnings on our severe weather warnings pages.

For the latest guidance to follow during the COVID-19 pandemic please visit the UK Government’s coronavirus advice page. Those living in ScotlandWales and Northern Ireland can access country-specific advice.

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Storm Alex, so why not Storm Aiden?

Many media outlets have been reporting that ‘Storm Aiden’ will batter Britain with strong winds and heavy rain this weekend. 

Over the last few days, weather forecasting computers – known as Numerical Weather Prediction (NWP) models – have been predicting a deep area of low pressure to develop close to the UK this weekend, bringing the potential for severe weather. Chief Meteorologists at the Met Office are closely monitoring developments.

Why do we name storms?

Since 2015 the Met Office, along with Met Éireann and KNMI, the national weather services in Ireland and the Netherlands, have been naming storms based on weather warnings in order to raise awareness of the potential impacts of severe weather.

Why do we name storms?

Latest NWP model output has moved the initial position of this weekend’s low-pressure system further south across France early on Friday. With very strong winds forecast, countries in the south-west Europe naming group – France, Spain, Portugal and Belgium – have named ‘Storm Alex’, which is the first name on their list for 2020-2021. The impacts further north were not considered strong enough for the Western European storm-naming group to name the system as ‘Storm Aiden’.

Later on Friday and over the weekend this system will move closer to the UK, bringing heavy rain and strong winds to many areas.

European Storm naming groups

When a storm is named by another weather service in Europe (see European storm naming groups image above) it is agreed that the same name will be used by all weather services in order to retain a consistent message.  Similarly, if a weather system impacting the UK were the remnants of a Hurricane that has moved across the Atlantic, we will use the same name, for example ex-Hurricane Ophelia in 2017.

This weekend, it will be wet and windy for many of us.  Keep an eye on the latest Met Office weather forecast and severe weather warnings where you are using our forecast pages and by following us on Twitter and Facebook, as well as using our mobile app.

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Climate Change: The perfect fuel for wildfires? 

As wildfires continue to rage in North and South America, Met Office Chief Scientist Professor Stephen Belcher examines what has led to the potentially record-breaking scale of fires and what science is needed to contain the risks

California wildfires

California firefighters tackling one of many wildfires which have raged across the eastern United States during 2020. Pic: Shutterstock.

Last year wildfires ravaged Australia. This year has seen reports of extensive fires in the Amazon, in California, and earlier this year during the hot spell, also in the UK. Even the area within the Arctic Circle is experiencing an extraordinary fire season, with thawing permafrost exposing large areas of carbon-rich peatlands, acting as additional fuel and a huge new source of greenhouse gas emissions. And it’s not just that we are seeing more in the news about wildfires, data shows the number of fires is increasing. By May this year, the number of wildfires recorded in South America was already higher than in any previous year since systematic monitoring began in 1998. And since the early 1970s, California’s annual wildfire extent has increased fivefold.

Wildfires are more severe during extended periods of hot dry weather, because higher temperatures cause more evaporation and that dries the vegetation, creating fuel for the fires. For example, last year, Australia saw very hot, dry, conditions caused by a pattern of temperatures in the Indian Ocean, known as the in Indian Ocean Dipole. The Indian Ocean Dipole is a natural fluctuation in the climate that affects the weather patterns around the world including in Australia, but now this fluctuation is adding onto a world that is warmer because of climate change.

So now that the globally-averaged temperature has risen to more than 1.0°C warmer than in the pre-industrial world, it is not surprising that we are seeing more wildfires around the world. Importantly though, higher temperatures alone will not necessarily lead to more fires. Fuel must be available and there needs to be an ignition source, either by human influence or lightning strikes. Climate change may also lead to wetter conditions in some places, as warmer air can hold more moisture, which can affect fuel availability and flammability.

In January this year, an international group of scientists, including from the Met Office, got together to survey the published scientific evidence and concluded  there is consistent evidence that hot dry weather conditions promoting wildfires are becoming more severe and widespread due to climate change.

So, we are going to continue to experience more wildfires as the climate changes. This is driving a need to provide forecasts that trigger fire prevention to limit accidental fires. At the Met Office we now produce forecasts of a ‘fire severity index’ for England and Wales. And earlier this year, scientists from the Met Office and from CEMADEN and INPE in Brazil, developed a technique to assess the likelihood of high fire conditions across South America during the riskier months of August to October. This is part of a broader move from traditional forecasting of weather into forecasting the impacts of weather.

Map of South America showing status of fire alert within protected areas

Map of South America showing status of fire alert within protected areas

Chantelle Burton a Climate Scientist at the Met Office who specialises in wildfire research, said: “By using computer simulations of the climate now, with the present-day levels of carbon dioxide, and comparing with computer simulations of the climate with pre-industrial levels of carbon dioxide, we can calculate how climate change has increased the chances of hot weather spells. These techniques are now being extended to calculate the role of climate change in increasing the chances of wildfires.”

Wildfires also pump additional carbon dioxide into the atmosphere, so can act as a ‘positive feedback’.  So, as the world warms, we expect more wildfires, that will further warm the climate. Putting numbers on this is a difficult task. Pioneering recent research at the Met Office has combined outputs from vegetation and climate models, paving the way for future climate projections to include wildfires.

If we are to meet the ambitious Paris Climate Agreement to keep global warming to below 2.0°C degrees above pre-industrial levels, then we must cap our atmospheric carbon dioxide levels. Additional release of carbon dioxide from wildfires reduces yet further the volume of fossil fuels that can be burnt whilst keeping global warming in line with the Paris Agreement. There are other natural processes that are likely to emit additional greenhouse gases into the atmosphere as the climate warms, for example permafrost melting in Siberia. But it’s all about numbers now. A high priority for climate science is to put numbers on these positive feedbacks through better measurements and improved computer models of the climate system so that we can plan for a future that keeps global warming to within the lowest possible limits.

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Atlantic tropical storms forming at a record pace

Author: Julian Heming, Met Office Tropical Prediction Scientist.

Update 21 Sept 2020

Shortly after publishing the blog below two more storms were named. A low pressure system near Portugal was named Subtropical Storm Alpha, which made landfall later on Friday 18th September. Then the  evening of the 18th Tropical Storm Beta formed, this storm is expected to come ashore over Texas soon.

There have now been a total of 23 named storms so far this season and this is the first time Greek names have had to be used in 15 years.

Original blog

The Atlantic region is currently setting a record-breaking pace for the formation of tropical cyclones. As of 18 September 2020, a total of 21 storms had formed – more than any other year on record at this stage in the June to November season. Only once have more storms been recorded in a season, that was 2005 when there were 28. There are 21 names on the Atlantic storm naming list, when these have been allocated letters from the Greek alphabet are used.  Therefore the next storm to be named will be Tropical Storm Alpha. However, that only paints part of the picture of what has been happening in the Atlantic and other parts of the northern hemisphere this year.

Active Atlantic

A combination of several climate factors is driving the active Atlantic storm season this year. A main driver is the development of La Niña conditions in the eastern Pacific, which acts to reduce wind shear over the Atlantic allowing storms to form more readily. High wind shear prevents or slows tropical storm formation. The sea-surface temperatures over large parts of the Atlantic have been higher than average and the west African monsoon has also been strong meaning the easterly waves which cross west Africa and produce Atlantic storms have been potent.

Although there has been a record number of Atlantic storm formations, eight have become hurricanes (winds 74 mph or greater) and just two have become a ‘major’ hurricane (winds 111 mph or greater). This is a lower proportion of hurricanes and major hurricanes than would be expected from a total of 21 tropical storms based on past climate figures. Also, several of this season’s storms were quite short lived, particularly early in the season. Thus, by some measures other than the number of storms, this season has had lower levels of activity than some previous seasons to date.

One feature of the current storm season is the high number of storms reaching landfall over the USA. Tropical Storms Bertha, Cristobal, Fay and Marco and Hurricanes Hanna, Isaias, Laura and Sally have all come ashore over the USA.

Hurricane Laura at landfall over Louisiana, USA seen on 27 August 2020.
Picture: RAMMB/CIRA.

Hurricane Laura was the strongest of these bringing wind gusts of over 130 mph and a storm surge of near 15 feet at its peak. Although weaker than Laura as measured by wind speed, Hurricane Sally became slow moving at landfall and dropped as much as 30” (750 mm) of rainfall over some parts of southern USA. In addition, Hurricane Paulette made landfall directly over Bermuda in the Atlantic Ocean. This is fourth hurricane landfall over this small Atlantic territory in the last six years.

Hurricane Paulette seen on 14 September 2020.
Bermuda can be seen in the eye of the hurricane. Picture: RAMMB/CIRA.

Meanwhile another tropical depression has formed in the Gulf of Mexico and is expected to become a hurricane over the next few days.

Atlantic tropical cyclones (ranging from tropical depression to hurricane)
seen on 14 September 2020. Picture: RAMMB/CIRA.

Elsewhere in the Globe

So have other parts of the globe seen similar levels of activity? In short, the answer is ‘no’. Both the eastern and western Pacific have seen tropical cyclone activity well below average to this point in the season. By one measure, the western Pacific has had only 40% of usual activity. However, some parts of this basin have still been hit hard. Two tropical storms (Hagupit and Jangmi) and three typhoons (Bavi, Maysak and Haishen) have all impacted the Korean Peninsula.

The North Indian Ocean has a split cyclone season and in the first half there were two cyclones. The strongest of these was Amphan which struck the India/Bangladesh border region and to date is the strongest tropical cyclone of the northern hemisphere season.

The Mediterranean Sea occasionally sees storms which have some characteristics of tropical cyclones – sometimes referred to as ‘medicanes’. In 2018 a particularly strong one, known locally as Zorbas, hit southern Greece causing some impacts. A medicane named Ianos, came ashore over the Greek island of Kefalonia overnight 17th to 18th September causing coastal flooding, downing trees and damaging buildings.

Mediterranean storm Ianos seen on 17 September 2020. Picture: Met Office/EUMETSAT.

Is climate change affecting tropical storm intensity and frequency?

The effects of climate change on tropical cyclone activity remains complex.  It is not possible to conclusively state the extent to which climate change may have influenced the frequency or intensity of this year’s North Atlantic Hurricane season. More research is needed to understand the relationships and relative contributions of the various physical processes at play and the way in which climate change is influencing them.

The Met Office’s latest summary of expected changes can be found here and is based largely on the IPCC Fifth Assessment Report.

Further Information

Follow our Twitter feed @metofficestorms for regular information on tropical cyclones currently active worldwide.

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A dull and damp August brings Summer to a close

Despite several notable weather events, neither the month of August nor the summer as a whole for 2020 will be remembered for being particularly prominent from a climatological point of view.

Although there was a major summer heatwave in the middle of the month of August for England and Wales, with temperatures reaching 36.4°C at Heathrow and Kew Gardens on 7th, more unsettled and cooler conditions at the start and end of the month balanced the month out. Much of the UK was above average for mean temperature in August, with East Anglia and the south east of England the highest over the long-term average. Suffolk, Kent and East Sussex were the counties with the highest mean temperatures compared to average (2.5°C above).

monthly_meantemp_2020-08_anomaly_1981-2010

It was a wetter than average month for most except for the south east of England and north west Scotland, where Sutherland only recorded 30% of its average monthly rainfall (31.5mm). Some regions recorded more than twice normal August rainfall, Herefordshire recorded 226% of its average for the month and Midlothian 228%. The hot spell of weather triggered some torrential downpours that saw 30-60mm falling in just a few hours, making up considerable proportions of monthly totals in single rain events.

monthly_rainfall_2020-08_anomaly_1981-2010

The only region to experience a sunnier than average August was north Scotland, with 119% of its average sunshine hours (139.7 hours). The UK as a whole only saw 88% of its average sunshine hours (142.6 hours).

monthly_sunshine_2020-08_anomaly_1981-2010

There were two named storms in August in quick succession that brought strong winds and heavy rain to parts of the UK. A turbulent spell of weather late in the month saw a strong jet stream bringing deep areas of low pressure towards the UK. Storms Ellen (19th to 21st) and Francis (25th) brought wind gusts of 46 to 58mph across inland areas and 58 to 70mph across exposed coastal locations. Wind speeds reached 79mph at Capel Curig, Conwy during storm Ellen and 81mph at Needles Old Battery (Isle of Wight) from storm Francis. These were two of the most notable August storms in the UK in the last 50 years but were not unprecedented.

Provisional August 2020  data Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 15.9 1.0 142.6 88 120.0 135
England 17.4 1.3 157.6 86 109.4 158
Wales 16.1 1.1 125.0 74 175.5 163
Scotland 13.5 0.5 128.4 96 116.6 100
N Ireland 15.0 0.6 108.3 80 156.2 161

Summer

For the season as a whole, the UK has been warmer than average (by 0.38°C), with the focus of above average mean temperatures in the south east of the UK. Warmer conditions in June and August have been partly offset by a cooler than average July. Suffolk had the highest mean temperature compared to average (+1.06°C)., County Fermanagh (-0.03°C), Kincardineshire (-0.22°C) and the City of Aberdeen (-0.13°C) were among only five UK counties to be below average for mean temperature through summer 2020.

seasonal_meantemp_2020-summer_anomaly_1981-2010

All three summer months have been wetter than average for the UK, although south east England and north west Scotland are the exceptions when looking at a more local level. Kent was the driest individual county compared to average, with 76% of the average summer rainfall (111.3mm). North west England, south west Scotland and Northern Ireland saw the wettest summer relative to average, with around 150% or more of average rainfall. This year joins a small cluster of years that have experienced a warm-wet summer, where more typically we might expect warm-dry or cool-wet.

seasonal_rainfall_2020-summer_anomaly_1981-2010

Sunshine has been below average in total duration, most notably so for Northern Ireland and Wales. The UK as a whole only had 89% (449.3 hours) of its average summer sunshine, with Northern Ireland only recording 73% (313.9 hours). Only a handful of counties in the south east of England and north Scotland recorded above average sunshine hours for summer 2020.

seasonal_sunshine_2020-summer_anomaly_1981-2010

Provisional Summer 2020  data Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 14.75 0.38 449.3 89 321.0 134
England 16.02 0.53 508.0 91 262.9 136
Wales 14.79 0.34 421.6 81 427.6 150
Scotland 12.78 0.21 383.0 90 374.5 123
N Ireland 14.01 0.11 313.9 73 399.3 157

 

 

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A cool July ends with notable heat

July 2020 was looking to be a fairly unremarkable month in terms of climate statistics for the UK, until hot conditions closed the month on the 31st.

Overall it was a cool month, with most days having temperatures below average. Successive low pressure systems brought cloud, rain and predominantly westerly winds across parts of the UK, keeping temperatures down. The UK as a whole was -0.8°C below the long-term (1981-2010) average for the month. As the anomaly map indicates, the south-east of the UK was the only region to get close to average temperatures for July.

One outlier of the July statistics is the maximum temperatures recorded on Friday 31st July. Tim Legg from the Met Office’s National Climate Information Centre, said: “An area of low pressure in the Atlantic acted to draw warm air up from the continent, bringing a day of heat to much of the UK with a particular focus on the south-east. The top temperature recorded was 37.8°C at Heathrow, with Kew Gardens in London close behind with 37.3 °C. This made it the hottest day of the year so far by some margin, and it also measures as the third hottest day on record in the UK.”

The only two hotter days than 31st July were 25th July 2019 when 38.7°C was recorded at Cambridge Botanic Gardens and 10th August 2003 when 38.5°C was recorded at Faversham in Kent.

The heat was short-lived with a cold front moving in from the west making some places 10°C lower the following day. Only Wisley, in Surrey, and Holbeach, in Lincolnshire, reached heatwave criteria, with Thursday, Friday and Saturday just reaching the temperatures required under the definition.

monthly_meantemp_2020-07_anomaly_1981-2010

tmean

Rainfall was above average across parts of Wales, north-west England and Scotland through the month with some locations in south-west Scotland and north-west England recording more than double the average July rainfall. This is also linked to the successive low pressure systems through the month, a product of the jet stream following a more southerly track than usual for the time of year. In contrast the south coast of England has been somewhat drier than average. West Sussex was the driest county compared to average, with just 52% (27.5mm) of its average rainfall for the month.

monthly_rainfall_2020-07_anomaly_1981-2010

rain

Sunshine has been below average at 83% (142.4 hours) overall for the UK. The east of Scotland and south of England saw close to average sunshine. It was particularly dull for Northern Ireland with just 59% (83 hours) of the average sunshine hours. Further evidence of areas of low pressure influencing the UK, especially in the west. The exception has been Shetland which has seen above average sunshine for the month with 136% (172.1 hours) of the long-term average (1981-2010) sunshine.

monthly_sunshine_2020-07_anomaly_1981-2010

sun

Provisional July 2020  data Mean temp (°C) Sunshine (hours) Rainfall (mm)
Actual  Diff from avg (°C) Actual % of avg Actual % of avg
UK 14.3 -0.8 142.4 83 95.2 122
England 15.6 -0.6 163.9 85 65.1 104
Wales 14.2 -0.9 140.7 79 115.0 124
Scotland 12.2 -1.1 118.0 84 135.4 137
N Ireland 13.6 -1.0 83.0 59 118.8 147

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Helping to forecast water demand during Covid-19

Lockdown during the Covid-19 pandemic has brought many changes and challenges to life in the UK.  Government guidance aimed to contain and reduce virus transmission has reshaped our day-to-day lives, from how much electricity we use, to the way we consume water.

Over the last few months, teams at the Met Office have been working with water companies to help identify the changes and trends in water use brought about during lockdown.

Before and after lockdown

Our teams compared water use before lockdown (February to early March) and at the beginning of lockdown (late March to early April).  As can be seen in Figure 1 below, most water companies have seen an increase in average water consumption during lockdown, with companies covering predominantly suburban areas (G and H) seeing the most noticeable increase, whereas companies operating in city areas see a reduction in water use (A).  The data also showed differences between weekday and weekend water consumption largely disappeared.

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Figure 1) Percentage change in daily average base water consumption for ten water companies in early lockdown (late March-early April) compared to before lockdown (February-early March)

Lockdown during March and May coincided with a prolonged spell of sunny, warm and very dry weather, which introduced a ‘fine spring weekend’ effect to every day.  The data suggests water use during this period is more sensitive to weather compared to pre-lockdown, with weather the main driver of day-to-day variations.  For example, an increase in temperature appears to cause a higher rise in water demand than it would pre-lockdown.  Figure 2 below shows an inexorable rise in water use to around 30% above base usage by late May, similar to the peak levels seen during the hot summer of July 2018.

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Figure 2) Percentage change in daily water consumption from average during lockdown. 

 

“Lots of us are spending more time at home and along with warm weather we’ve seen customers using water differently”, said David Hinton, Chief Executive at South East Water.  “Increased demand for tap water in our area is more akin to patterns we see in an exceptionally hot summer.  More water is being used on DIY projects and gardening which is contributing to the additional 25% of water we’re treating and pumping through our water distribution system.”

Working together to help keep taps flowing

Water demand models do not currently take into account these new water use patterns observed during lockdown.   This has created new operational challenges for water companies, who despite having sufficient water supply in their reservoirs, are unable to treat and pump water fast enough to meet the unexpectedly high demand at peak times.

“By working together with water companies and sharing experiences, we can more accurately analyse the effect of lockdown on water use”, said Nick Law, Senior Account Manager at the Met Office.  “From this the Met Office has produced a ‘COVID’ sensitive model that our colleagues in the water companies involved in this research can use to adjust their demand planning and better anticipate water usage as this new way of life continues.”

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What can be done to better prepare for the future?

This year’s summer months may bring particular challenges to water companies, as normal population movements during summer holidays are impacted by Covid-19 restrictions.  Water companies that normally experience a noticeable drop in water use during holidays could experience an increase in water demand, due to a combination of lockdown and spells of warm summer weather.

The challenge now is to understand how peak Summer demand levels can be forecast and managed, to ensure supplies can be maintained” said Ian Savage, Strategic Control Manager at Thames Water. 

Based on modelling during lockdown so far, the Met Office can perform scenario planning for an extended period of lockdown for different weather types in July and August. This will allow the water industry to better anticipate water demand during periods of lockdown restrictions and plan for different weather scenarios, as this new way of life continues.

 Want to find out more? 

If you’re interested in learning more about how we’re helping the water industry forecast and manage water demand, check out our recent article published in Utility Week. 

 

Posted in Met Office News