Details available for: sunshine - rainfall - wind - temperature - snow - visibility

See also Scotland - England - Northern Ireland climates.

On the whole, Wales is cloudier than England, because of the hilly nature of the terrain and the proximity to the Atlantic. Even so, the south-western coastal strip of Dyfed manages an annual average total of over 1,700 hours of sunshine (also achieved by many places along the south coast of England). The dullest parts of Wales are the mountainous areas, with annual average totals of less than 1,100 hours.

Mean daily sunshine figures reach a maximum in May or June, and are at their lowest in December. The key factor is, of course, the variation in the length of the day through the year, but wind and cloud play their part as well.

Facts and Figures (bright sunshine)

Maximum duration in a month: 354.3 hours at Dale Fort (Dyfed) in July 1955.

Minimum duration in a month: 2.7 hours at Llwynon (Powys) in January 1962.

Sunshine Graph

Rainfall in Wales varies widely, with the highest average annual totals being recorded in the mountainous areas of Snowdonia and the Brecon Beacons, where the yearly fall is comparable with that in the English Lake District or the western Highlands of Scotland. In the east, close to the border with England, annual totals are similar to those over much of the English Midlands. Snowdonia is the wettest part of Wales with average annual totals exceeding 3,000 mm, but coastal areas and the east receive less than 1,000 mm a year.

Throughout Wales, the months from October to January are significantly wetter than those between February and September, unlike places in south-east Scotland or in the English Midlands where July and August are often the wettest months of the year. This is a reflection of the relatively low frequency of thunderstorms in Wales, compared with that in England. For example, at Cardiff, thunder occurs on an average of 11 days a year, compared with 15 to 20 at many places in England. In the west and north-west the frequency declines to around eight days per year.

Facts and Figures

Maximum in a day (09-09 UTC): 211 mm at Rhondda (Gwent) on 11 November 1929.

Rainfall Graph

There is a close relationship between surface isobars (lines joining points of equal air pressure) and wind speed and direction over open, level terrain. However, local topography also has a very significant effect, with winds tending to be aligned along well-defined valleys.

Over land, the roughness of the ground causes a decrease in the mean wind speed compared with that which occurs over the sea, with the size of the decrease depending on the nature of the terrain. In major towns and cities the overall mean speed is considerably reduced by the buildings but local funnelling may occur, and the wind may gust to about the same speed as in open country. It is this gustiness which causes much of the damage to buildings and trees during storms.

A day of gale is defined as a day on which the mean wind speed at the standard measuring height of 10 m above ground attains a value of 34 knots (39 miles per hour, 17.2 metres per second) or more over any period of 10 minutes during the 24 hours. The strongest winds in Britain are associated with the passage of deep depressions across or close to the country; these are most frequent during the winter, so that is when gales are most frequent. These depressions are usually at their most intense over the open Atlantic Ocean; thus at low altitudes in Wales, gales occur most frequently in the extreme south-west of Dyfed with about 30 days of gale on average. Other coastal areas have 15 days or more of gale with the number of days decreasing inland to five days or fewer.

In general, wind speed increases with height, with the strongest winds being observed over the summits of hills and mountains. There are no wind-recording stations at high altitudes in Wales so no data can be given; as an indication however, Snaefell on the nearby Isle of Man (at 615 metres) averages over 200 days of gale a year.

Facts and Figures

Highest gust recorded at a low-level site: 108 knots (124 mph) at Rhoose (South Glamorgan) on 28 October 1989.

Wind Graph

Over Wales the mean annual temperature at low altitudes varies from about 9.5 °C to 10.5 °C, with the higher values occurring around or near to the coasts. The mean annual temperature decreases by approximately 0.5 °C for each 100 m increase in height so that, for example, Bwlchgwyn in Clwyd (at 386 m) has an annual mean temperature of 7.3 °C. On this basis, Snowdon (at 1,085 m) would have an annual mean temperature of about 5 °C.

In winter, temperatures in the British Isles are influenced to a very large extent by those of the surface of the surrounding sea, which reach their lowest values in late February or early March. Around the coasts February is thus normally the coldest month, but inland there is little to choose between January and February as the coldest month.

The coldest nights are those on which there is little wind, skies are clear, and there is a covering of snow on the ground; the lowest temperatures occur away from the moderating influence of the sea, on the floors of inland valleys into which the cold air drains. It was under such conditions that the temperature fell to -23.3 °C, the lowest ever recorded in Wales, at Rhyader on 21 January 1940. Coastal areas do not experience such cold nights; as an example, the lowest temperature ever recorded at Brawdy in Dyfed is -10.7 °C on 13 January 1987. At the opposite extreme, some of the highest winter temperatures in the British Isles have been recorded in North Wales. These high winter temperatures (up to 18 °C on occasion) occur when a moist south to south-easterly airflow warms up downwind of Snowdonia after crossing the mountains, an effect known as the föhn after its more dramatic manifestations in the Alps.

July is normally the warmest month in Wales, and the highest temperatures of all have occurred furthest away from the cooling influence of the Atlantic. The highest temperature ever recorded in Wales is 35.2 °C at Hawarden Bridge in Clwyd, on 2 August 1990.

Facts and Figures

Air temperature (measured under standard conditions at 1.25 m above the ground).

Highest recorded 35.2°C at Hawarden Bridge (Clwyd) on 2 August 1990.

Lowest recorded -23.3°C at Rhayader (Powys) on 21 January 1940.

Snow is comparatively rare near sea level in Wales, but much more frequent over the hills. The average number of days each year when sleet or snow falls in Wales varies from about 10 or less in some south-western coastal areas to over 40 in Snowdonia. Snow rarely lies on the ground at sea level before December or after March, and the average number of days with snow lying in Wales varies from six or less around the coasts to over 30 in Snowdonia.

The number of days of snowfall and snow cover varies enormously from year to year. At many places in the last 50 years it has ranged from none at all in several winters to in excess of 30 days during the winters of 1946/47 and 1962/63. Even places near the coast experienced prolonged snow cover during these two winters.

In heavy snowfalls there can be quite extensive drifting of the snow in strong winds, especially over the higher ground, resulting in severe dislocation of transport. Fortunately such occasions are rare, but one of the worst snowstorms this century in South Wales occurred on 7 and 8 January 1982, when depths of one metre or more were commonplace, with severe drifting and power lines brought down.

Facts and Figures

Snow Graph

Given the distance of many parts of Wales from the industrial and populous areas of Britain and mainland Europe, much of Wales enjoys excellent visibility. The Principality's industrial areas are all close to the coast, and are thus relatively breezy and free of serious reductions of visibility by reason of smoke.

Inland and over high ground in Wales fog statistics are scarce, but given the mountainous nature of the country and its proximity to the sea, hill fog can be both extensive and frequent and is a potential hazard to be borne in mind by walkers in Snowdonia and the Brecon Beacons.