Theme: Climate of the United Kingdom

Northern Ireland
Northern Ireland is warmer than Scotland throughout the year. Maximum temperatures are milder than in Wales from December to April, and milder than in England from December to February, but Northern Ireland is cooler during the rest of the year. Sunshine totals in every month are more than those of Scotland, but less than those of the rest of Great Britain. Northern Ireland is drier and has fewer rainy days than Scotland throughout the year, except in May, when it rains on more days. Northern Ireland is also drier than Wales in every month, yet it rains on more days. The rainiest month is January, when 17.8 days have more than 1 mm (0.04 in) of rain on average.
Scotland
Scotland is generally cool compared to the rest of the UK, and the climate at altitude merges into Cfc on the Köppen system, with average minimum temperatures in January of −0.2 °C (31.6 °F). The Central Lowlands have higher temperatures during the summer than any other part of Scotland, and have also broken some records for the whole of the UK. Aviemore is considered one of the coldest inhabited places, with its inland location and an altitude of about 210 metres. The wettest month in Scotland is January; most months are wetter than other parts of the UK, except for the late spring to early autumn months.
Wales
Wales has warmer temperatures throughout the year than Northern Ireland and Scotland and has milder winter minima than England, but cooler winter maxima than Northern Ireland. Wales is wetter throughout the year than Northern Ireland and England, but has fewer rainy days than Northern Ireland; meaning that rainfall tends to be more intense. Wales is also drier than Scotland in every month apart from May, June and December, and there are fewer days with rain than in Scotland. Sunshine totals throughout the year are more than that of Scotland and Northern Ireland, but less than that of neighbouring England. May is the sunniest month, averaging 186.8 hours
Seasons
Spring
Spring is the period from March to May. Spring is generally a calm, cool season, particularly because the Atlantic has lost much of its heat throughout the autumn and winter. As the sun rises higher in the sky and the days get longer, temperatures slowly rise, but the solar effect is mitigated somewhat by the effect of the cool ocean waters and westerly winds that blow across them.
There is a fair chance of snow earlier in the season when temperatures are colder; often in March. Some of the country's heaviest snowfalls of recent years have happened in the first half of March, and snow showers can occur infrequently until mid-April. They have been known to develop as late as mid-May over some areas of the country, such as in 2013 when snow was recorded on 14 May over parts of Staffordshire, Herefordshire and Wales. Snow was also recorded at lower levels in early June 1975. More recently, there was a disruptive snow event between 26 and 29 April 2016 across much of Northern England and Scotland, which was unusually the only significant snow event of the winter 2015/16. Snow, frost and ice can be disruptive and damaging to flowering plants, particularly later in the spring.
Early spring can be quite cold, and occasionally the lowest temperature of the winter can occur in March, as it did at Heathrow Airport on 5 March 2001, 4 March 2006 and 8 March 2011. Temperatures below freezing are not unusual in March, even in the south of the UK. On the other hand, high temperatures above 30 °C (86 °F) are generally rare, but can occur on occasion; most recently on 25 May 2012. It was even hotter on 27 May 2005, when 31.9 °C (89.4 °F) was recorded in London. Rarely, the hottest day of the year can be in spring. As stated below, 27 May was the hottest day of the year in 2012 in most parts of the UK. In Aberdaron, the hottest day of 2011 was very early on in the year on 21 April. Temperatures in March seldom reach 20 °C (68 °F), as they did in 1990, 1993, 2012 and 2017, and this temperature is usually reached for the first time in April or May. Throughout spring, there can be large temperature swings between day and night. On 9 April 2017, night-time temperatures fell to just 3 °C (37 °F) at Northolt, but 25 °C (77 °F) was reached in the afternoon. Warmth in spring depends almost entirely on the strength of the sun, and can trigger thunderstorms and downpours.
Mean temperatures in Spring are markedly influenced by latitude. Most of Scotland and the mountains of Wales and northern England are the coolest areas of the UK, with average temperatures ranging from −0.6 to 5.8 °C (30.9 to 42.4 °F). The southern half of England experiences the warmest spring temperatures of between 8.8 and 10.3 °C (47.8 and 50.5 °F).
Summer
Summer lasts from June to August and is the warmest and usually the sunniest season. There can be wide local variations in rainfall totals due to localised thundershowers. These thundershowers mainly occur in southern, eastern, and central England and are less frequent and severe in the north and west. Climatic differences at this time of year are more influenced by latitude and proximity to the ocean. Temperatures are the highest in southern and central areas and lowest in the north. Hot weather above 27 °C (81 °F) in most places and in most years occurs on multiple days per year, but more frequently in London and south-east England where temperatures can exceed 30 °C (86 °F) and less so in parts of Scotland. The record maximum is 38.7 °C (101.7 °F), recorded in Cambridge on 25 July 2019. Heatwaves and occasional droughts occur in Britain such as in the summers of 2003, 2006 and recently in 2018 when forest fires broke out in parts of England.

Autumn
Autumn in the United Kingdom lasts from September to November. The season may be a little more unsettled; as cool polar air moves southwards, it can meet warm air from the tropics and produce an area of disturbance along which the country lies. This can combine with the warm ocean due to heating throughout the spring and summer, to produce some unsettled weather. In addition, the land may become colder than the ocean, resulting in significant amounts of condensation and rain-bearing clouds.
Atlantic depressions at this time can become intense, and winds of hurricane force (greater than 119 km/h or 74 mph) can be recorded. Western areas, closest to the Atlantic, experience these severe conditions more often than eastern areas. Autumn, particularly the latter part, is often the stormiest time of the year. One particularly intense depression was the Great Storm of 1987. A very severe storm also affected the UK on 27 October 2002. At Mumbles Head near Swansea, a maximum sustained wind speed of over 123 km/h was recorded: equivalent to a Category 1 hurricane. The autumn of 2013 was also littered with severe storms, including the St. Jude's Storm on 28 October 2013.
Autumn can sometimes be a cold season - in recent years, very low temperatures and heavy snowfall have been recorded during November 1985, November 1993 and November 2010. There was a new record low of −18.0 °C (−0.4 °F) in Wales on 28 November 2010. At Northolt, in Greater London, the coldest temperature of the year 2016 was set on 30 November. Snow also fell rather widely across the UK on 28–29 October 2008, causing traffic problems where it settled on the M4. Even further south, low temperatures can be recorded, with temperatures well below freezing as far south as Heathrow Airport on 29–31 October 1997, with a lower temperature than any recorded at this station in March, November or December 1997 and even the following January 1998; only on 2 and 4 February 1998 were lower temperatures recorded here that winter. The first frost of the winter usually occurs between October and December; frost is quite unusual in September, when the surrounding ocean is at or near its warmest, except on high ground. It is not particularly unusual for September to be warmer than June, as it was in 1999.
However, the United Kingdom sometimes experiences an "Indian summer", when temperatures, particularly by night, can be very mild and rarely fall below 10 °C (50 °F). Such events are aided by the surrounding Atlantic Ocean and seas being at their warmest, keeping the country in warm air, despite the relatively weak sun. Examples of this were in 1985, 1999, 2005, 2006, 2011and 2016 when September saw above average temperatures which felt more like a continuation of summer than autumn. Autumns since 2000 have generally been very mild, with notable extremes of precipitation; the UK has seen some of its wettest and driest autumns since the millennium. 2011 and 2016 were notable as many areas of the country recorded their highest temperatures of the year in September and October (for example, 28.2 °C (82.8 °F) at Hawarden on 1 October, 26.3 °C (79.3 °F) at St. Athan on 2 October 2011 and the UK's highest temperature of 2016 on 13 September with 34.4 °C (93.9 °F) at Gravesend). On 13 October 2018, temperatures reached 26.5 °C (79.7 °F) at Donna Nook in Lincolnshire, the latest in the year such a high temperature had been recorded. Temperatures on the night of 12–13 October were also just under 20 °C (68 °F) in London.
Coastal areas in the southern half of England have on average the warmest autumns, with mean temperatures of 10.7 to 13.0 °C (51.3 to 55.4 °F). Mountainous areas of Wales and northern England, and almost all of Scotland, experience mean temperatures between 1.7 and 7.5 °C (35.1 and 45.5 °F).

Hardiness zones in the British Isles. Based on the USDA system and used to indicate growing conditions for plants.
Winter
Winter in the UK is defined as lasting from December to February. The season is generally cool, wet, windy, and cloudy. Temperatures at night rarely drop below −10 °C (14 °F) and in the day rarely rise above 15 °C (59 °F). Precipitation can be plentiful throughout the season, though snow is relatively infrequent despite the country's high latitude: often the only areas with significant snowfall are the Scottish Highlands and the Pennines, where at higher elevations a colder climate determines the vegetation, mainly temperate coniferous forest, although deforestation has severely decreased the forest area. For a majority of the UK, snow is frequent in winter time yet is usually light and doesn't last long, apart from the higher altitudes, where snow can lie for 1–5 months or even beyond 6 months.
Towards the later part of the season the weather usually stabilises with less wind, less precipitation and lower temperatures. This change is particularly pronounced near the coasts, mainly because the Atlantic Ocean is often at its coldest at this time after being cooled throughout the autumn and the winter. The early part of winter however is often unsettled and stormy; often the wettest and windiest time of the year.

Snow cover on The Saddle in the Scottish Highlands
Snow falls intermittently and mainly affects northern and eastern areas, high ground in Wales and especially the mountains of Scotland, where there is often enough snow lying to permit skiing at some of the five Scottish ski resorts. These resorts usually operate between December and April, depending on the snowfall. Frequently in the mountains potent depressions may move in from the north in the form of "polar lows", introducing heavy snow and often blizzard-like conditions to parts of the United Kingdom, particularly Scotland. Blizzards have become rarer in the 21st century, although much of England was affected by one on 30 January 2003. During periods of light winds and high pressure, frost and fog can become a problem and can pose a major hazard to drivers.
Mean winter temperatures in the UK are most influenced by proximity to the sea. The coldest areas are the mountains of Wales and northern England, and inland areas of Scotland, averaging −3.6 to 2.3 °C (25.5 to 36.1 °F). Coastal areas, particularly those in the south and west, experience the mildest winters, on average 5 to 8.7 °C (41.0 to 47.7 °F). Hardiness zones in the UK are high, ranging from zone 7 in the Scottish Highlands, the Pennines and Snowdonia, to zone 10 on the Isles of Scilly. Most of the UK lies in zones 8 or 9. In zone 7, the average lowest temperature each year is between −17.7 and −12.3 °C (0.1 and 9.9 °F), and in zone 10, this figure is between −1.1 and 4.4 °C (30.0 and 39.9 °F).
Snow falls in the UK almost every year, but in small quantities. The UK can suffer extreme winters like 1684, 1740, 1795 (when London had its record lowest temperature of −21.1 °C (−6.0 °F), 1947 and 1963. In 1962 it snowed on Boxing Day, and snow lasted in most areas until 6 March, with blizzards through February, which had significant and documented effects on the FA Cup - Wrexham were forced to play on sand for one tie. In recent times snow has generally become rarer, but the UK can still get heavy falls, such as in 1978-79, 1981–82, 1986-87 and 1990-91. The winter of 2008/09 produced the heaviest snowfall since 1991 between 1 and 3 February, and the winter of 2009-10 was even more severe, with many parts of the United Kingdom having the coldest and snowiest winters since 1978/79; temperatures plummeted to −22.3 °C (−8.1 °F) at Altnaharra, Sutherland – close to the −22.9 °C (−9.2 °F) recorded in Antarctica in the same period. The lowest temperature ever recorded in the UK was −27.2 °C (−17.0 °F), on 10 January 1982 and 11 February 1895 in Braemar, Scotland and on 30 December 1995 in Altnaharra. December 2010 was the coldest December in 120 years; the CET (Central England Temperature) was −0.7 °C (30.7 °F); it was the coldest month since February 1986, and the coldest December since 1890. Many places had heavy snowfall and extreme cold, temperatures regularly fell below −10.0 °C (14.0 °F) across many areas. However, the cold subsided after Christmas Day, 2010. November 2010 saw an extremely severe cold snap, with lows of −18.0 °C (−0.4 °F) in Llysdinam on 28 November. The month saw temperatures below average, despite what was actually a very mild first half. Spring 2013 was also cold: March 2013 was the coldest month of the winter (and indeed 2013 as a whole), which is quite striking given that December 2012, January and February 2013 were all also below average in terms of temperature. The following winter was the opposite: in many places, only on 11 and 12 January was any snow recorded (some places having no snow at all), and the entire country was battered by a series of severe depressions and storms. The St Jude's Day storm first affected the UK on 26 October 2013, and many places saw no respite until a high swept across the country on 2 March 2014. Some places in the Somerset Levels remained under water for most of the winter and well into spring. Record-equalling gusts of 142 mph were recorded off the north coast of Scotland on 5 December 2013, with notably severe storms also recorded on 2 November 2013, 24 December 2013, 3 January 2014 and 14 February 2014.
In the 1990s and 2000s, most of the winters were milder and usually wetter than average, with below-freezing daytime temperatures a rare occurrence. In fact, the winter of 1995/1996 was the only one which was defined as below average in terms of the UK as a whole, although February 1991 saw heavy snowfall and January 1997 was cold in the South. The winters of 2008/09, 2009/10 and 2010/11, however, had below or well below average temperatures, with large snowfall amounts widespread and very low temperatures; this was the first series of three consecutive cold winters in the UK since the 1960s. The winter of 2012/13 was very cold too, although the peak of the cold was in March. The winter of 2014/2015 was an oddity: it was generally quiet and sunny. December 2014 and January 2015 were a little milder than the average; February 2015 was close to normal. The winter of 2016/17 was very nearly a very cold winter owing to the presence and position of high pressure, although ultimately only November 2016 was cold widely as a whole. Early December 2016 was cool and January 2017 was cold in the south-east, with much of the rest of England and Wales near the 1961-1990 average. At Northolt, the average daily minimum for January 2017 was below freezing for the first time since December 2010. The winter of 2017/18 was then much colder than average too. However, mild temperatures prevailed during winter 2018/19.
December 2015 was the wettest calendar month ever recorded in the United Kingdom, and January 2016 the second wettest. In these months, some northern and western parts had 2 to 4 times as much rainfall as normal. December 2015 was also the warmest December averaged over the whole UK, and the CET had the warmest December on record. (CET was 9.7 °C (49.5 °F), this is warmer than even any March). Most areas of southern England had average monthly temperatures 5-6 deg. C above normal. Some plants flowered that would normally do so in the spring. Hardly any stations in Wales and Southern England recorded any air frosts, and temperatures were often comparable to those of April or May. The maximum recorded temperature was 17.2 °C (63.0 °F) at Teignmouth in Devon and Plockton and Achnagart in the Highlands of Scotland on the 16th. The lowest daily mean temperature during December 2015 at Heathrow Airport was 8.2 °C (46.8 °F) (on 9 December), comparable to the average daily high for the calendar month. However, December 2015 did not break any national records for high temperatures, just failing to reach the maximum England temperature of 17.7 °C (63.9 °F) recorded on 2 December 1985 in Chivenor, Devon and on 11 December 1994 in Penkridge, Staffordshire. Despite the warmth, it was the dullest December since 1989.