Details available for: sunshine - rainfall - wind - temperature - snow - visibility
See also England - Wales - Northern
Generally, Scotland is more cloudy than England, due mainly to
the hilly nature of the terrain and the proximity of low-pressure
systems from the Atlantic. Even so, parts of Angus, Fife, the Lothians,
Ayrshire, and Dumfries and Galloway average over 1,400 hours of
sunshine per year. This compares favourably with the coastal areas
of Northern Ireland and the north of England, though not perhaps
with the annual totals of over 1,700 hours achieved along the south
coast of England. The dullest parts of Scotland are the more mountainous
areas, with an annual average of less than 1,100 hours of sunshine
over the mountains of the Highland region.
Mean daily sunshine figures reach a maximum in May or June, and
are at their lowest in December. Wind and cloud play their part,
but the key factor is, of course, the variation in the length of
the day through the year. The relatively high latitude of Scotland
means that although winter days are very short, this is amply compensated
by long summer days with an extended twilight. On the longest day
there is no complete darkness in the north of Scotland. Lerwick,
in Shetland, has about four hours more daylight (including twilight)
at midsummer than London.
Facts and Figures (bright sunshine)
Maximum duration in a month: 329 hours at Tiree (Argyll and Bute)
in May 1946 and May 1975.
Minimum duration in a month: 0.6 hours at Cape Wrath (Highland)
in January 1983.
There is a general misconception that the whole of Scotland experiences
high rainfall. In fact, rainfall in Scotland varies widely, with
a distribution closely related to the topography, ranging from over
3,000 mm per year in the western Highlands (comparable with rainfall
over the mountains of the English Lake District and Snowdonia in
Wales) to under 800 mm per year near the east coast (comparable
with the Midlands of England). (Note that rainfall also includes
snow, which is melted and measured as rainfall.)
Typically, measurable rainfall (an amount of 0.2 mm or more) occurs
on over 250 days per year over much of the Highlands, decreasing
to around 175 days per year on the Angus, Fife and East Lothian
coasts. In comparison, the driest part of Britain, along the Thames
Estuary in south-east England, averages around 150 days per year
with measurable rainfall.
The frequency of thunderstorms in Scotland, around three to nine
days per year, is relatively low compared with an average of nine
to 15 days over England. The number of thunderstorms can vary widely
from year to year, but in general the northern and eastern coasts
of Scotland average only three or four days with thunder per year,
whilst inland values range from nine in the south to six in the
Facts and Figures
Maximum in a day (09-09 UTC): 238 mm at Sloy Main Adit, Loch Lomond
on 17 January 1974.
The most common direction from which the wind blows in Scotland
is the south-west, but the wind direction often changes markedly
from day to day with the passage of weather systems. There is a
close relationship between surface isobars (lines joining points
of equal air pressure) and the wind speed and direction over open,
level terrain. However, in mountainous areas local topography also
has a significant effect, with winds tending to blow along well-defined
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
the gusts which cause much of the damage to buildings and trees
during major storms. In general, wind speed increases with height,
with the strongest winds being observed over the summits of hills
Since many of the major Atlantic depressions pass close to or over
Scotland, the frequency of strong winds and gales is higher than
in other parts of the United Kingdom. Over low ground, the windiest
areas are the Western Isles, the north-west coast and Orkney and
Shetland with over 30 days with gales per year in some places. 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.
Facts and Figures
Highest gust recorded at a low-level site: 123 knots (142 m.p.h.)
at Fraserburgh (Aberdeenshire) on 13 February 1989.
Highest gust recorded at a high-level site: 150 knots (173 m.p.h.)
at Cairngorm Automatic Weather Station (on the border of Highland
and Moray at an altitude of 1,245 m AMSL) on 20 March 1986.
Over Scotland the mean annual air temperature at low altitude ranges
from about 7 °C on Shetland, in the far north, to 9 °C on the coasts
of Ayrshire and Dumfries and Galloway in the south-west. Normally
temperature decreases by approximately 0.6 °C for each 100 m rise
in height so that over the high ground temperatures are generally
colder. For example, Braemar (at 339 m above mean sea level) has
an annual mean temperature of 6.4 °C, while the corresponding value
on Ben Nevis (at an altitude of 1,344 m) is -0.3 °C.
To a large extent, winter temperature in the British Isles is influenced
by the surface temperature of the surrounding sea, and as the North
Sea is cooler than the waters off the west coast, the east coast
is generally slightly cooler in winter than the west coast.
In general, January and February are the coldest months. The daytime
maximum temperatures over low ground in Scotland in January and
February average around 5 to 7 °C, but on rare occasions in the
lee of high ground, temperatures can reach up to around 15 °C when
a moist south or south-westerly airflow warms up after crossing
the mountains, an effect known as the föhn after its more dramatic
manifestations in the Alps.
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 inland, away from the moderating influence of
the sea, in valleys into which the cold air drains. It was under
such conditions that the temperature fell to -27 °C, the lowest
recorded in Britain, at Braemar in Aberdeenshire on 10 January 1982
and also more recently at Altnaharra in Highland Region on 30 December
1995. Coastal areas do not experience such cold nights; as an example
the lowest temperature recorded at Lerwick on Shetland in the thirty
years 1961 to 1990 is only -8 °C.
In summer, the effect of latitude on the amount of heat received
from the sun plays a major role in determining the temperature.
Thus, temperatures in Scotland are generally a few degrees cooler
than in England. For example, the average daily maximum temperature
at Glasgow in July is 19 °C compared with 22 °C in London.
July and August are normally the warmest months in Scotland. The
highest temperatures normally occur inland, away from the moderating
influence of the cooler sea. The highest air temperature recorded
in Scotland was 32.9 °C at Greycrook (Scottish Borders) on
9 August 2003.
Facts and Figures
Air temperature (measured under standard conditions at 1.25 m above
Highest recorded 32.9 °C at Greycrook (Scottish Borders)
on 9 August 2003.
Lowest recorded -27.2 °C at Braemar (Aberdeenshire) on 11
February 1895 and 10 January 1982. Minus 27 °C was also recorded
at Altnaharra (Highland) on 30 December 1995.
As temperature generally decreases with height, precipitation which
reaches the ground as rain at low-level sites may fall as snow over
higher ground. Consequently, there is a marked increase with altitude
in the number of days with snow falling and also the number of days
with snow lying on the ground. The average number of days with sleet
or snow falling in Scotland ranges from around 20 or less near the
west coast to over 100 days in the Cairngorm Mountains and some
other high peaks.
Snow rarely lies on the ground at sea level before November or
after April. On low ground in the Western Isles and in most coastal
areas of Scotland, snow lies on average for less than 10 days a
year, although this increases to around 15 to 25 days for coasts
in the north and north-east. However, over the mountains snow typically
lies for more than 50 days a year. Serious difficulties with roads
blocked by snow are, fortunately, not common on low ground, but
some higher roads in Scotland are regularly affected each year.
In heavy snow there can be quite extensive drifting of the snow,
especially over the higher ground. Snow is deposited on leeward
slopes with exposed areas often left relatively bare. Snow deposited
in natural hollows, such as high-level corries, can persist for
some considerable time (an effect utilised to good effect by the
development of the skiing industry in Scotland) and a few of these
high-level, north-facing, localised snow beds are semi-permanent,
only disappearing in very occasional summers. On the highest summits,
such as Ben Nevis, snow cover typically persists for around six
or seven months of the year.
Facts and Figures
Scotland often enjoys excellent visibility, since the greater part
of the country is remote from the industrial and populous areas
of Britain and mainland Europe. Even in the industrial areas of
central Scotland the move away from coal fires for domestic heating
and the decline in traditional heavy industry has reduced the incidence
of smoke haze caused by local air pollution. Frequently, however,
cloud with a very low base can shroud high ground with hill fog.
Extensive hill fog often results, especially in the west, when a
moisture-laden south-westerly airstream covers the country. The
resulting low visibility, especially if further reduced by drizzle,
can pose a hazard for hill walkers and motorists.
Radiation fog may form overnight in low-lying inland areas on clear,
calm nights, particularly in winter. Sea fog from the North Sea,
known locally as 'haar', sometimes ruins what would otherwise be
a fine day on or near the east coast, or in the Northern Isles,
between April and September. Both these types of fog tend to break
up and disperse during daytime, although inland, particularly in
winter, mist and fog does sometimes persist. At Edinburgh, the midday
visibility is less than 1,000 m on 3% of December days.