The climate of south-west England is classed as oceanic (Cfb) according to the Köppen climate classification. The oceanic climate is typified by frequent cloudy skies, cool winters with cool summers and precipitation all year round, with more experienced in winter. Annual rainfall is about and up to on higher ground. Exceptions include areas to the east of high ground (e.g. Exeter / parts of West Somerset that are subject to a rain shadow effect and annual rainfall is closer to 30 inches).
Summer maxima averages range from in the Scillies to in the east north-east of the region and winter minima averages range from in the north-east of the region to across the extreme south-west of Cornwall and the Scillies. Cold snaps are generally less intense or prolonged in the south west and rarely does the temperature fall below . Similarly, prolonged heat is fairly rare, however in recent years there have been more heatwave related conditions, albeit fairly short affairs but in July 2022 temperatures have hit in Bude and other parts of the region temperatures were between widely in more inland locations.
The south west is the second windiest area of the United Kingdom, the majority of winds coming from the south-west and north-West. Government organisations predict the area will experience a rise in temperature and become the hottest region in the United Kingdom.
Inland areas of low altitude experience the least amount of precipitation. They have the highest summer maxima temperatures, but winter minima are lower than those of the coast. Snowfalls are more frequent in comparison to the coast, but less so in comparison to higher ground. They experience the lowest wind speeds and the total sunshine hours are between those of the coast and the moors. This typical climate of inland areas is more noticeable the further north-east into the region.
In comparison to inland areas, the coast experiences high minimum temperatures, especially in winter, and slightly lower maximum temperatures during the summer. Rainfall is lowest at the coast and snowfall there is rarer than the rest of the region. Coastal areas are the windiest parts of the peninsula and they receive the most sunshine. The general coastal climate becomes more prevalent further south-west into the region.
The south-west has areas of moorland inland such as Bodmin Moor, Dartmoor and Exmoor. Because of their high altitude they experience lower temperatures and more precipitation than the rest of the south west (approximately twice as much rainfall as lowland areas). Both of these factors also result in the highest levels of snowfall and the lowest levels of sunshine. Exposed areas of the moors are windier than the lowlands and can be almost as windy as the coast.
Sunshine is highest on the coast as convective clouds tend to form slightly inland as the ground heats up faster. Annual amounts are around 1700-1800 hours for places like Torquay, Penzance, Newquay and Teignmouth, whilst inland areas such as Yeovil, Tiverton, Crediton and Exeter are cloudier, prone to fog and consequently 1450-1600 hours are more typical.
Definition Information in this article relates to the Met Office definition of south-west England, which covers Cornwall, Devon, Somerset, North Somerset, Bath and North East Somerset, South Gloucestershire, the City of Bristol and the Isles of Scilly. This is a smaller area than the UK Government's South West England region, which also covers Gloucestershire, Wiltshire and Dorset. The region is also sometimes loosely described as the West Country.
Temperature The south-west experiences a seasonal temperature variation, although it is less extreme than most of the United Kingdom. This is because the sea is in closer proximity to inland areas of the south-west than inland areas of most of the United Kingdom and the sea has less seasonal temperature variance. The sea is coldest between February and March; as a result Cornwall and Devon are coldest in February with daily minima ranging from in inland Devon to on the Isles of Scilly. The sea has less influence towards the north-east of the region, causing January to be the coldest month with mean minimum temperatures from or . In the months of July and August (the hottest part of the year) daily maxima range from about on the coast of Cornwall to across inland areas of the north-east (Somerset and North Somerset) and also Exeter due to being situated in the Eastern Lee of Dartmoor.
The sea surrounding the south-west peninsula has the highest annual mean temperature of any sea in the United Kingdom, with a temperature close to . Coastal areas of Cornwall and the Isles of Scilly experience annual mean temperatures similar to that of the sea as the prevailing wind is from the sea. Towards the north-east of the region, the annual mean temperature decreases and is closer to just over . The sea's influence on annual temperature range is highest in west Cornwall, where the range is approximately . In the north-east of the region, the range is approximately . Inland areas are affected by their altitude: the mean temperature decreases as altitude increases. Princetown on Dartmoor, with an altitude of , has a mean temperature of .
The sea's influence in the south-west usually prevents cold temperatures, however temperatures can plummet during periods of cold easterly air flow: all of which have been recorded in January. In 1987 the minimum temperature recorded at St Mawgan, Cornwall was and was noted on the Isles of Scilly. Inland areas have experienced even colder conditions with at Exeter International Airport, Devon in 1958 and at Bastreet, Cornwall in 1979. Further to the north-east of the region, temperatures reached in Yeovilton, Somerset in 1982.
Extremely high temperatures (heat waves) are rare in the south-west. Their occurrence is caused by a dry south-easterly air flow off Mainland Europe or the short-lived 'Spanish plume', (caused when low pressure sat to the south west of the UK and High pressure over the Low countries /southern North Sea creates a southerly airflow that sucks up hot air originating from Iberia, and as it crosses Bay of Biscay it picks up moisture and raises humidity levels to uncomfortable levels).
Combined with strong summer sunshine, the temperature rockets: The hottest recorded temperature in the south west is , on 17 July 2022 at Bude Cornwall. Overnight lows can be uncomfortable, not dropping below , 20 °C being classified as a ‘tropical night’.
Sunshine
Average annual sunshine totals rise above 1,600 hours along the coast—higher totals are recorded on the region's southern coast at the English Channel than on its northern coast along the Bristol Channel. 1,400–1,600 hours of annual sunshine are to be expected in inland areas of the south west. In June 1925, the highest monthly sunshine totals were recorded: 381.7 hours at Pendennis Point, Cornwall and 334.8 hours at Long Ashton, Somerset. During the winter months, which are the dullest, less than 20 hours of monthly sunshine have occasionally been recorded. In December 1998 there were 20 days without sun recorded at Yeovilton.
In general, June is the sunniest month, because the days are at their longest, and December is the dullest. The Azores High affects the south-west of England as it extends north-eastwards towards the British Isles. The Azores is more influential in summer. The high pressure reduces cloud cover through the process of subsidence. In spring and summer, the sea is cool compared to the air temperature, causing less convective cloud cover. The convective cloud forms more frequently inland, especially on higher ground such as Dartmoor, Exmoor and Bodmin Moor, thus reducing the amount of sunshine. Coastal areas of the south-west have more hours of sunshine.
Rainfall Most of the rainfall in the south-west is caused by Atlantic depressions or by convection. Most of the rainfall in autumn and winter is caused by the Atlantic depressions, which is when they are most active. In summer, a large proportion of the rainfall is caused by sun heating the ground leading to convection and to showers and thunderstorms.
The Isles of Scilly have annual rainfall totals of about . Coastal areas of Cornwall and Devon typically receive of rainfall annually. The altitude increases the amount of rainfall. Highland areas are cooler, causing moist air to cool below the dew point as it rises over high ground forming clouds and then rain. Princetown is from Plymouth and higher, and has double the rainfall. Areas that fall in the rain shadows (lees) of higher ground have lower levels of rainfall: near Exeter (east of Dartmoor) and in parts of central Somerset (east of Exmoor). The Mendip Hills, to the north-east of the region, receive over per year and the Bath–Bristol area receives around .
The sea reaches its highest temperature in late summer/autumn and its lowest in late winter/spring. As a result, the highest rainfall can be expected in autumn and lowest in spring. The months with the most rainfall are in autumn and winter. Monthly rainfall can be variable. On the coast, most months have recorded less than and, some months, less than at some point. The wettest station of the region, Princetown, has recorded of rain during May.
The number of days with at least of rainfall correlates to the pattern of quantity of rainfall. In late spring/summer, 9–10 days per month recorded rain in coastal areas, 7–9 days in the north-east and 12–13 days at high altitude (Princetown). In winter these values increase to 15–16 on the coast, 12–13 in the north-east and over 18 days in high altitude.
Very heavy rainfall, spanning 5–15 hours, is rare in the south-west. Instances include the Lynmouth disaster of 15 August 1952, caused by of rainfall falling locally on Exmoor over 12 hours. Also, on 8 June 1957, fell at Camelford, Cornwall and in June 1917, fell in 13 hours in Bruton, Somerset. The north-Cornish village of Boscastle was flooded on 16 August 2004; a peak hourly rainfall of was recorded. Approximately 100 people had to be rescued by helicopter and 116 cars were swept out to sea.
From December 2013 onwards the Somerset Levels suffered severe flooding as part of the wider winter storms of 2013–14 in the United Kingdom. The Levels are a low-lying area around above mean sea level (O.D.) which have been prone to flooding from fresh water and occasional salt water inundations. People have attempted to drain the area for hundreds of years. During December 2013 and January 2014 heavy rainfall led to extensive flooding with over 600 houses and of agricultural land, including North Moor, Curry and Hay Moors and Greylake, affected. The village of Thorney was abandoned and Muchelney cut off.
Snowfall
Snowfall normally occurs between November and April and short snowfalls can occur between October and May on higher ground. The snow usually only settles between the months of December and March. Snow rarely falls when temperatures are greater than and for snow to settle temperatures must normally be lower than .
In the south-west the number of days of snowfall increases with altitude: per approximately every increase in altitude, the number of days of snow falling increases by five days. From 1979 to 2000, on average there were fewer than 10 days per winter in which snow fell in the islands of the south-west and the coastal areas of Devon and Cornwall, and slightly more than 10 days on average near to the Severn Estuary. Inland areas received between 8–15 days of snow falling; more days of snow fall were noted particularly to the north-east. Some upland areas received, on average, over 25 days per year of snow falling.