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The disruptive snowfalls and very low temperatures of late 2010

John Prior and Mike KendonMet Office, Exeter

From late November until Christmas 2010 the UK experienced two spells of severe winter weather, with very low temperatures and copious amounts of snow. Transport organisations, local authorities, utilities and emergency services were put under great pressure and everyday life and business were disrupted. There were echoes of the conditions experienced during the previous winter, from late December 2009 to mid-January 2010 (Prior and Kendon, 2011).

The first spell began on 24 November and lasted until 9 December, bringing the most widespread and significant snowfalls so early in the winter since 1965. The second spell lasted from 16 to 26 December, with the snowfalls and low temperatures the most significant in December since 1981. This article describes the weather and its impact during both spells, makes compari-sons with previous years and looks at the aftermath of this second consecutive winter with severe weather.

Late November to early December After a largely unremarkable autumn, dur-ing the last week of November 2010 north-easterly or easterly winds brought bitterly cold air from northern Europe and Siberia, heralding the early arrival of winter. Persistent snowfalls affected eastern Scotland and northeast England as the air-stream picked up moisture over the North Sea, and during the following two weeks all parts of the UK experienced hard frosts, with most also seeing significant snow.

On the evening of 23 November, showers in the north of Scotland turned to snow on high ground. Snow fell to low levels in Scotland on the 24th, spreading to north-east England during the 24th and 25th and, as the flow off the North Sea persisted, snow depths across eastern Scotland and north-east England steadily increased. Wintry showers also affected west Wales during the 25th, and outbreaks of snow spread

southeastwards across Wales and south-west England on the 26th.

Temperatures failed to rise above freezing in many inland areas from the 27th. There were hard overnight frosts, with tempera-tures dipping to − 10°C widely from Wales and the Midlands northwards early on the 28th. The minimum of −18.0°C at Llysdinam (Powys) on the 28th broke a long-standing November record for Wales and –11.9°C recorded at Mucker Broughderg (County Tyrone) approached the November record for Northern Ireland (see Table 1). The maxima of –5.6°C at Llysdinam and –1.6°C at Castlederg (County Tyrone) on the 28th also set new records for November.

With little melting, the snow continued to accumulate across high ground. By 0900 UTC on the 30th, there was 25cm of lying snow

across many eastern and central areas of Scotland, with 41cm at Cromdale (Highland), 44cm at Nunraw Abbey (East Lothian) and 58cm at Balmoral (Aberdeenshire). Similar depths had built up in parts of northeast England, away from the coast, with 40cm at Kielder Castle (Northumberland) and 30cm at Carlton-in-Cleveland (North Yorkshire). On the 30th, snow spread westwards across the north Midlands and southeast England, with accumulations of 15–20cm locally. The hourly snow depths measured at five stations dur-ing this period are shown in Figure 1.

By 0900 UTC on 1 December, snow lay over 15cm deep across much of eastern Scotland and eastern England from Lincolnshire northwards (and a few places elsewhere, such as Surrey and Staffordshire). Over 30cm had accumulated in some upland areas.

Table 1

Lowest daily minimum temperatures recorded in November 2010.

Country Temperature (°C)

Location Date November record (°C)

Location Date

England −13.5 Topcliffe (North Yorkshire )

28th −15.5 Wycliffe Hall (North Yorkshire)

24 Nov. 1993

Wales −18.0 Llysdinam (Powys)

28th −11.7 Welshpool (Powys)

9 Nov. 1921

Scotland −16.1 Altnaharra (Highland)

29th −23.3 Braemar (Aberdeenshire)

14 Nov. 1919

Northern Ireland

−11.9 Mucker Broughderg (County Tyrone)

28th −12.2 Lisburn (County Antrim)

15 Nov. 1919

Figure in bold denotes new record set.

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Figure 1. Time series of hourly snow depths in eastern Scotland and northeast England, 25 November to 12 December 2010. The locations are Aviemore (Highland) [ ], Dyce (Aberdeen) [ ], Gogarbank (Edinburgh) [ ], Redesdale Camp (Northumberland) [ ], and Albemarle (Northumberland) [ ].

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Snow showers continued in many eastern areas of Scotland and England during the 1st and 2nd, adding to the accumulations and expanding the snow cover, with over 20cm in parts of Surrey and Sussex. Even southern coastal areas were affected, with 13cm at Shanklin (Isle of Wight), and 9cm at Guernsey airport - the greatest depth there in early December for at least 50 years. There was even lying snow at Land’s End (Cornwall).

Daytime temperatures widely remained below freezing, and with winds gusting over 40kn (46mph) along much of the east coast of England there was significant wind-chill. In lighter winds, overnight temperatures in many northern and western areas fell below −10°C. On the 2nd, after falling to −21.3°C soon after 0900 UTC, the temperature at Altnaharra (Highland) rose no higher than a remarkable −14.0°C in the period 0900–2100 UTC (the ‘day-time maximum’). As the easterly winds finally eased, temperatures fell below −7°C widely early on the 3rd, with −20.0°C at Ravensworth (North Yorkshire), the lowest December tem-perature in England since 1981.

During the weekend of 4/5 December, temperatures in the south rose to around +3 to +5°C widely, allowing a slow thaw here; lying snow melted in most areas to the south of a line from south Wales to the Wash. North of this, however, the snow-fields were undiminished, depths widely being in excess of 20cm.

The night of 5th/6th saw the cold weather return, with a hard frost in all areas, and it was particularly cold in the north, with widespread minima below −10°C. On the 6th, temperatures again struggled to rise above freezing, especially across much of inland Wales and the Midlands, whilst in places freezing fog persisted for most of the day. Several long-established stations recorded their coldest December day, including maxima of −6.8°C at Church Fenton (North Yorkshire) and −4.5°C at Shobdon airfield (Herefordshire). It was the turn of central Scotland and Northern Ireland to see the heaviest snowfalls: during the morning of the 6th over the Central Belt depths increased to 15–20cm, with 30–40cm or more locally. At 0900 UTC on the 7th, a depth of 29cm was recorded at Gogarbank (Edinburgh) and 54cm at Nunraw Abbey (East Lothian).

The 7th and 8th saw widespread frost as well as freezing fog that was slow to clear in some southern areas. Temperatures on both nights fell well below −10°C across much of Scotland, Northern Ireland and northern England. Daytime maxima were also very low, being around −5°C in mid-Wales, Lincolnshire and central Scotland on the 7th (−8.8°C at Strathallan (Perthshire)) and in Cumbria on the 8th (−7.9°C at Carlisle). A cloudy, northwesterly flow on the 9th heralded a milder interlude and lying snow began to thaw.

Impacts of the first spellThe freezing temperatures and deep snow from this first spell caused serious disrup-tion, particularly across eastern Scotland and northeast England. Higher routes in Scotland were closed due to drifting snow and there was a spate of accidents. Motorists were stranded overnight 28/29 November on the A9 between Dunblane and Perth after several lorries jack-knifed. Electricity supplies were cut to 3000 homes, mostly in Perth and Tayside. By the 29th, more than 800 schools in Scotland, 400 in England and 100 in Northern Ireland were closed.

As the snow spread to other parts of east-ern and southern England on the 30th, so did the travel disruption. Four hundred lor-ries were trapped on the M25 in Surrey overnight 30th/1st, with difficult driving conditions and road closures elsewhere. For much of the 1st the A90 Forth Road Bridge was closed due to heavy snow, for the first time in its 46-year history. Gatwick and Edinburgh airports were closed on the 1st and 2nd, and rail services were delayed or cancelled. Three hundred rail passengers were stranded on a train in Sussex overnight 1st/2nd and more than 100 drivers spent two nights in their vehicles on the A57 in South Yorkshire. About 6500 schools were closed across the UK by the 3rd. Emergency hospital admissions rose markedly due to accidents and falls involving snow and ice, and in Cumbria two elderly people were found dead in their gardens.

On Saturday 4th, rain showers in Wales falling on freezing surfaces resulted in wide-spread black ice, numerous accidents and cancelled bus services. The sporting sched-ule of the weekend 4th/5th, from football to horse racing, was hit hard by severe weather, especially in Scotland. The snow on the morning of Monday 6th brought further major transport problems to Scotland. In the Central Belt, motorways and trunk roads

including the M8, M74 and A9 were at a standstill with hundreds of drivers again stranded overnight. Train and bus services were delayed or suspended and Edinburgh and Glasgow airports were closed.

In parts of northwest England rain falling on to very cold road surfaces early on the 9th formed ice, leading to numerous accidents and the closure of some trunk roads and motorways.

Mid to late December The milder interlude lasted almost a week until very cold Arctic air spread southwards during the 16th, introducing the second spell of severe weather. Most of the UK again experienced snow, which lay until Christmas with no significant melting, accompanied once more by very low temperatures, excep-tionally so across Northern Ireland.

On the 17th, snow showers affected northern Scotland, Northern Ireland, north and west Wales and southwest England giv-ing accumulations of 10–20cm quite widely. On the 18th, an area of prolonged snow moved eastwards across central southern England to London with depths of 10cm typically, and 24cm at South Newington (Oxfordshire). This event is described in detail in this issue by Webb (2011). The 18th was exceptionally cold, with a maximum of −11.0°C1 at Castlederg in Northern Ireland. A bitterly cold night followed, the tempera-ture at Shawbury (Shropshire) falling to −19.6°C. Snow showers continued in the northeast and the far south on the 19th and another very cold night followed, with tem-peratures again well below −10°C widely and −18.0°C1 at Castlederg (Figure 2). Early on the 20th, heavy snow fell across southwest England, 10–15cm accumulating widely and around 25cm locally. The snow spread

Figure 2. Hourly air temperature at Castlederg, 49m amsl, from 24 November to 27 December 2010. Between 0500 UTC on 18 December and 2300 UTC on 25 December (187 hours) the air tempera-ture was continuously below −5°C (denoted by the blue arrow), falling below −15°C on 6 nights and briefly reaching −15°C again at 1900 UTC on the 25th. The record minimum of −18.7°C is also marked. Note the sudden thaw on Boxing Day, the temperature rising 18 degC in 18 hours.

1New Northern Ireland record, subsequently broken a few days later.

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complete snow cover, the exceptions includ-ing west Pembrokeshire, west Cornwall, the Isle of Wight, Lincolnshire (partially obscured) and parts of southern Ireland.

The last bitterly cold night was that of 25/26 December, with temperatures again widely falling below −10°C, and to −16.5°C at Exeter Airport. The cold weather relented during the last few days of December as milder Atlantic air moved in from the south-west; temperatures returned to near normal across most parts with a thaw of lying snow.

Impacts of the second spellThe very cold, snowy conditions across southern England caused widespread dis-ruption for travellers and Christmas shop-pers over the weekend 18/19 December. Hundreds of thousands of airline passengers were affected as Heathrow airport closed at its busiest time of the year, and there were flight delays or cancellations elsewhere. Many people spent one or more nights in airport terminals. The snowfalls in southwest England early on the 20th resulted in trunk-road closures in Devon and Somerset. Travel delays mounted elsewhere, with continuing cancellation of flights and train services, including Eurostar. The AA reported Monday 20 December as the busiest-ever day in its 105-year history, with some 28 000 breakdown calls.3 On the 21st, East Coast train services from London were suspended after overhead power lines came down near Huntingdon. Further snowfalls on the 22nd across north Wales and the Midlands caused difficult travelling conditions, but fortunately the situation then gradually improved.

any month (Table 2). Early on Christmas Day, the temperature at Exeter Airport (Devon) fell to −15.0°C, while the maximum of −7.8°C at Llysdinam set a new Welsh record for December. However, in most northern areas the temperature on Christmas Day rose above freezing, for the first time since 16 December in many inland parts of north-ern England and Scotland.

The satellite image in Figure 4 captures the ‘White Christmas’2 experienced by most of the British Isles. This shows almost

further east during the day. Figure 3 shows the snow depths at 0900 UTC on the 20th, when accumulations in this second spell peaked across most of the UK.

Temperatures fell well below −10°C over-night 20th/21st across the northern half of the UK, even near the coast, with −11.9°C at Blackpool (Lancashire) and −10.5°C at Scar borough (North Yorkshire). Snow con-tinued in the Midlands and parts of Wales at times through the 21st and 22nd, with the intervening night seeing temperatures well below −12°C inland across the north. At Altnaharra, the 24-hour daily maximum of −13.8°C from 0900 UTC on 21 December to 0900 UTC on 22 December bears compari-son with the UK record of −15.9°C at Fyvie Castle (Aberdeenshire) on 29 December 1995. It was followed by a minimum of −20.8°C on the morning of the 22nd and a daytime maximum of −15.8°C, the lowest in the UK for the month. Hard frosts also extended to west Cornwall, with −5.4°C at Culdrose on the 22nd.

It remained very cold, but dry and bright, as high pressure became established in the run-up to Christmas. Early on the 23rd the temperature at Castlederg fell to −18.7°C, while Edenfel (County Tyrone) recorded a daily maximum of only −11.3°C, each set-ting new records for Northern Ireland for

Table 2

Lowest daily minimum temperatures recorded in December 2010.

Country Temperature (°C)

Location Date December record (°C)

Location Date

England −20.0 Ravensworth (North Yorkshire)

3rd −25.2 Shawbury (Shropshire)

13 Dec. 1981

Wales −17.5 Capel Curig (Conwy)

20th −22.7 Corwen (Denbighshire)

13 Dec. 1981

Scotland −21.3 Altnaharra (Highland)

3rd −27.2 Altnaharra (Highland)

30 Dec. 1995

Northern Ireland

−18.7 Castlederg (County Tyrone)

24th −16.1 Katesbridge (County Down)

28 Dec. 2000

Figure in bold denotes a new record.

Figure 3. Snow depths (cm) at 0900 UTC on 20 December 2010.

2A ‘White Christmas’ in the sense of snow cover rather than snow falling. About 20% of the official station network (mostly in the north) reported sleet/snow falling, whilst about 80% of the network had snow lying at 0900 UTC.3http://www.publications.parliament.uk/pa/cm201011/cmselect/cmtran/writev/weather/m6.htm Included in written evidence from the AA to the House of Commons Transport Committee.

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As temperatures rose to around normal after Christmas, lying snow became increas-ingly confined to higher ground. However, the thaw brought new problems as burst water pipes led to supply shortages in parts of Scotland and Wales. Worst affected was Northern Ireland, where a week of sub-zero temperatures – without precedent in over 100 years – resulted in numerous burst water mains and pipes. The subsequent rapid thaw soon led to serious shortages, resulting in interruptions to water supplies to some 215 000 properties.

Comparisons with previous years

Data sourcesComparisons with previous months have been made using monthly temperature series from 1910 for the UK, its constitu-ent countries and regions. These are based upon 5km grids, produced using the methods of Perry and Hollis (2005). The monthly Central England Temperature (CET) series from 1659 (Manley, 1974), daily CET series from 1772 (Parker et al, 1992) and historic station series provide longer-term perspectives. For snowfall, there are 5km grids of days with snow lying from 1961 (based upon 0900 utc station observations) and station records of snow depth at 0900 utc (mostly digi-tised from 1959). UK climate statistics are available at http://www.metoffice.gov.uk/weather/uk/ climate.html

Both of the two spells of severe winter weather were unusual in their own right and, because they were separated by only a week, December 2010 undoubtedly stands out in the UK climate record as one of the most remarkable months in the last 100 years. It was exceptionally cold, with the mean UK temperature 5 degC below the 1971–2000 average (Figure 5). Monthly mean minimum temperatures in parts of Northern Ireland, central Wales and Scotland were as much as 7 degC below normal. In the last 100 years it was easily the coldest December, the sixth-coldest calendar month, and the coldest month since February 1986 over the UK generally. In Northern Ireland it was the coldest month in the series, and for Scotland only February 1947 was colder (Table 3).

The mean Central England temperature was −0.7°C and, in this 352-year series, only the December of 1890 was colder (−0.8°C). However, the two spells of severe weather did not coincide with the calendar month of December. To take this into account, the daily mean CET series from 1772 has been analysed in terms of 30-day rolling means. From 28 November to 27 December 2010 the mean CET was −1.5°C. Lower values

Figure 4. A satellite image of the British Isles on 24 December 2010 from the NERC Satellite Receiving Station, Dundee University, Scotland http://www.sat.dundee.ac.uk/. Although it is unusual for the UK to be both cloud-free and almost entirely covered by lying snow, similar images are also available for 2 December 2010 and 11 months earlier on 7 January 2010.

Figure 5. Mean temperature in December 2010, anomaly expressed in terms of the 1971–2000 average. By some margin, these are the greatest negative anomalies for December in the last 100 years.

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have occurred during only 12 winters, all for periods beginning later – in December, January or February – and only two of these winters (1946/1947 and 1962/1963) were since 1900.

The records at Armagh Observatory have been digitised from 1865 and thus provide a longer record than the Northern Ireland areal series from 1910. The mean tempera-ture of −0.4°C made it the coldest December since 1878 and the equal third-coldest month in this series, with only January 1881 and February 1895 colder. The daily maxi-mum temperature was 0°C or below for 7 consecutive days from 18 to 24 December, the longest such spell since one of 13 days in January 1881. The daily maximum of

−8.0°C on 21 December 2010 was the lowest in this 146-year record.4

At Castlederg, the remarkable 187 hours below −5°C shown in Figure 2 was easily the longest such spell in digitised data for all stations in Northern Ireland. At Aldergrove (County Antrim), the temperature was 0°C or below for 155 hours between 1600 UTC on 19 December and 0300 UTC on 26th, the longest such spell in hourly data for this location from 1949: the previous record was 101 hours in January 1958.

Across much of the UK there was lying snow on over 20 mornings (Figure 6), typically at least 15 more than the 1971–2000 average for December. The snowfalls were the most pro-longed and widespread in December since 1981, when more than 10cm lay across much of Scotland, northern England, the Midlands and East Anglia from the 8th until New Year (the temperature fell to −25.2°C at Shawbury

Table 3

Rankings for the mean temperature in December 2010, compared to all months in series from January 1910.

Mean temperature Dec. 2010 (°C)

1971–2000 anomaly (degC)

Rank (nth coldest of all months

from 1910)

Coldest month since

Coldest month in series and mean temp (°C)

Previous coldest December in series and

mean temp (°C)

UK −0.9 −5.0 6th Feb. 1986 Feb. 1947, −2.0 Dec. 1981, 0.1England −0.4 −5.1 = 7th Feb. 1986 Jan. 1963, −2.3 Dec. 1981, 0.2Wales −0.5 −5.3 6th Feb. 1986 Jan. 1963, −2.5 Dec. 1981, 0.8Scotland −1.8 −4.8 2nd Feb. 1947 Feb. 1947, −2.4 Dec. 1981, −0.7N Ireland −0.7 −5.4 1st — Dec. 2010, −0.7 Dec. 1950, 1.4

Figure 6. Number of days in December 2010 with snow lying at 0900 UTC.

(Shropshire) on 13 December 1981). Figure 7 shows that, in terms of the number of days with snow lying, December was the snowiest month across England and Scotland since January 1979, and over Wales since January/February 1963. In Northern Ireland it was the snowiest month for more than 50 years. Further details of winters 2009/2010, 1978/1979, 1962/1963 and 1946/1947 are given in Prior and Kendon (2011).

With northeasterly or easterly winds and an absence of Atlantic fronts, less than a third of the average precipitation was recorded across most of Wales, western England and western Scotland, and this was the driest December in the UK since 1963.5 December was also a very sunny month in the west – where it was among the sunniest Decembers in the series which goes back to 1929. However, parts of southern England were very dull, with around 20 hours of sunshine, or less, for the whole month in the London area.

In terms of depth, persistence and area affected, the late November snowfalls were the most significant so early in the winter since 1965. During the second half of November 1965, snow was widespread and heavy at times across Scotland and the northern half of England and towards month-end it lay 30cm deep across Northumberland and County Durham (Meteorological Office, 1966). Despite a generally mild first half, November 2010 ranks about 10th coldest in mean tempera-ture series from 1910, and in Scotland and Northern Ireland it was the coldest November since 1985.

The very cold spells in November and December, together with similar conditions at the start of the year and a cool late summer, helped to make 2010 the coldest year in the UK since 1986 and the 12th coldest in the last 100 years. This is in marked contrast to other recent years, with 2002–2007 ranked as the warmest six in the last 100. The cold year of 2010 in the UK is probably linked to the negative phase of the North Atlantic Oscillation (Scaife et al., 2008). However, globally, 2010

4The previous lowest daily maximum tempera-ture was −5.6°C on 4 January 1867.

5Note – this is winter 1963/1964, not winter 1962/1963! Since rain-gauges may not capture precipitation fallen as snow, caution is needed with the December 2010 precipitation figures.

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was observed to be the warmest year on record – a fact that was predicted as ‘more likely than not’ by the Met Office in December 2009.7

The aftermath During January the weather gradually reverted to a milder Atlantic type, espe-cially across the southern half of the UK, although the cold air was reluctant to loosen its grip further north. By February, all parts were generally mild and frost–free; in contrast to December this was the mild-est February since 2002, with a marked absence of frost. Britain took stock of the disruption and damage that had occurred, and various government and industry enquiries took place. Coming so soon after disruption during the severe weather of winter 2009/2010, inevitably these raised questions about preparedness and led to a resolve to improve this.

The outcomes included:

• The British Airports Authority announced a £50m Heathrow investment plan, fol-lowing the report of the Heathrow Winter Resilience Enquiry. This plan included new snow-clearing and de-icing equip-ment, increased resources and improved passenger information systems (British Airports Authority, 2011).

• The House of Commons Transport Committee made various recommenda-tions about road, rail and air transport. These concentrated on improving

resilience to severe winter weather, information provision for road users and the welfare of air and rail passengers. They included assessment of how the electrified rail network south of the Thames could be made more resilient, with the setting up of a working group involving Network Rail, the train opera-tors and other interested parties. An investment of £10m in Met Office com-puting power for production of seasonal forecasts was also recommended (House of Commons, 2011).

• After the water supply problems in Northern Ireland, an investigation by the Utility Regulator found flaws in the execution of emergency plans, espe-cially in relation to communication with customers (Utility Regulator, 2011). Northern Ireland Water accepted the recommendations of this report in early March.

• The UK economy suffered as businesses were disrupted by transport problems and the construction industry experi-enced delays, with an estimate that transport disruption alone cost some £280m per day. The severe weather was blamed for a contraction in the UK econ-omy in the last quarter of 2010, after four quarters of growth (Office for National Statistics, 2011).

• The farming industry was left to count the cost of damaged crops, collapsed livestock buildings and burst pipes. In eastern Scotland and northeast England, the roofs of hundreds of farm buildings collapsed under the weight

of 50cm of snow. In parts of eastern England, such as Lincolnshire, brassica crops were badly affected with reports of up to 80% of the cauliflower crop lost. The total industry loss was esti-mated as over £100m (Farmers Weekly, 2011).

The effects of the severe conditions on the natural environment were mixed:

• In parks and gardens, many less hardy plants and trees were badly damaged by the snow and severe frost. Even the famous palm trees of the English Riviera, along the south Devon coast, suffered quite badly after the temperature fell to around −5°C on several nights towards and over Christmas.

• Fears about the UK’s bird population fortunately appeared largely unfounded. A survey of garden birds by the Royal Society for the Protection of Birds in late January 2011 showed that the popula-tion of some smaller birds such as gold-crests, long-tailed tits and coal tits actually made a significant come-back following a dramatic decline during the previous hard winter of 2009/2010.8 However, other species struggled to survive, including the rare Dartford war-bler as the snow enveloped its habitat on the lowland heaths of southern England.

PhotographsThe front cover of this issue shows Budleigh Salterton (Devon) on Christmas morning, some five days after snow fell – a remark-able survival for a south-facing beach in southwest England. The photograph on the inside front cover shows the ice on the nor-mally free-flowing lower section of the River Exe that had formed after about four days of very cold weather, making conditions dif-ficult for water birds such as swans. Figure 8 is a reminder of the difficulty of making weather observations during severe winter conditions. Climbing a frozen waterfall such as that shown in Figure 9 is only pos-sible after a prolonged period of freezing temperatures.

AcknowledgementsThe authors acknowledge, with thanks, the care and dedication of observers at co-operating climate stations and Met Office sites in recording severe weather, enabling studies such as this to be made. Also, the help of Kevin Rowlands, Matthew Clark, Francois Bocquet and Glen Harris of the Met Office with the sourcing of photographs is much appreciated.

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Figure 7. Number of days with snow lying6 for England, Wales, Scotland and Northern Ireland for the snowiest months since 1961. December 2010 is shown in bold, with bars coloured according to month. The 1971–2000 averages for December are: England 1.9 days, Wales 2.3, Scotland 5.2, Northern Ireland 1.6.6Based on station observations of snow covering at least half the ground at 0900 UTC, gridded at 5km resolution then averaged over each country.

8Results of the RSPB Big Garden Birdwatch can be seen at http://www.rspb.org.uk/birdwatch/.

7See http://www.metoffice.wgov.uk/news/releases/archive/2010/record-temperatures.

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Figure 8. Hoar frost at RAF Shawbury (Shropshire) at 1030 UTC on 7 December 2010. The air temperature was −7.7°C with a minimum that morning of −10.0°C. The instruments are (back) a Kipp & Zonen sunshine recorder which is heated, (middle) a disused Campbell-Stokes sunshine recorder and (front) a Kipp & Zonen solar radiation sensor. (Copyright Kevin Rowlands, Met Office.)

Figure 9. The frozen Torpentau Waterfall in the Brecon Beacons, south Wales on 5 December 2010. The fall is east-facing at 650m asl. Climber Francois Bocquet, Met Office. (Copyright Francois Bocquet, Met Office.)

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Correspondence to: Mike Kendonmichael.kendon@metoffice.gov.uk

© British Crown copyright, the Met Office, 2011 published with the permission of the Controller of HMSO and the Queen’s Printer for Scotland

DOI: 10.1002/wea.874

The heavy snowfall of 18 December 2010 across

the English south MidlandsJonathan D. C. WebbTornado and Storm Research Organisation (TORRO), Oxford

IntroductionThe protracted early winter cold of late 2010 was attributable to two surges of intensely cold Arctic air across these islands (Prior and Kendon, 2011). The first, in late November, was from the northeast and out-standing for the heavy convective snowfalls originating over the still-warm seas, with

some associated convective streamers extending inland downwind of coastal inlets. However, the sheltered south Midlands1 had relatively trivial amounts of snow. In contrast, during the second cold wave (from the north), a small cyclonic development resulted in a significant,

indeed locally very heavy, snow event across this region on 18 December.

Synoptic background By 0000  UTC2 on the 18th a complex area of low pressure had settled across Britain, Ireland and adjacent seas in particularly deep cold air. The 1000–500mbar thickness chart for 0000h showed that much of Great Britain was under sub-516dam air, and over the entire UK and all but the southwest tip of

2All times refer to UTC.

1For the purpose of this article, the south Midlands comprises the counties of Gloucestershire, Herefordshire, Worcestershire, Warwickshire, Oxfordshire, Northamptonshire, Buckinghamshire, Bedfordshire and Hertfordshire.