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Immortalised in the shipping news, Fair Isle’s weather is famous to many radio listeners. In earlier centuries the weather ruled the life of the island. A change in climate meant the difference between an acceptable harvest and a failed harvest; the difference between a successful fishing trip or disaster.
In more recent years, it meant a full larder or making supplies last until the weather relented enough to allow the island’s mailboat, the Good Shepherd, to risk a trip across to Shetland for supplies and mail.
Even today, with a 5/6-days-a-week air link to Shetland, a breakwater and plans for a new Good Shepherd, the weather continues to dominate island life. While agriculture and fishing may perhaps no longer be as all important as they once were, climate change is bringing greater threats to everyone and everything on this planet – not just this island.
The Fair Isle climate
At almost 60° north, Fair Isle’s climate is far from typical of what might be expected at this latitude, due to the ameliorating effect of the North Atlantic Drift. The mean annual temperature is now 8.3°C. The difference between the mean temperatures of the warmest and coldest month is around 8°C, and so the climate is best described as hyperoceanic.
Because of its position close to one of the major depression tracks, the weather on Fair Isle is very changeable. While the prevailing wind direction may be south-westerly, during spring there are frequent south-easterly winds, gradually becoming north-easterly during May, and by June the most frequent direction is north-westerly. South-easterly is again the prevailing wind direction in autumn.
Fair Isle is probably one of the windiest lowland sites in the British Isles, experiencing gales (10 minute mean speed of 34 kt/17.5 ms-1, or more) on an average of 58.4 days each year. While periods of calm, or very light wind conditions, are very rare, they can occur even in winter – but seldom last for more than an hour or two. In recent years, with an increased number of depressions crossing southern parts of the UK, strong north-easterly winds have increased in frequency.
Due to the rain-shadow effect of the Scottish mountains, rainfall is not excessive, but precipitation is frequent, with measurable rainfall on 216–266 days each year. The relative humidity is the highest in Britain and, except in late spring and early summer, cloudy conditions prevail. Winters are generally mild but frequently stormy. Summers are cool, often breezy, with a high frequency of fog, commonly associated with a south-easterly airflow.
During spring and summer Fair Isle often reports the lowest daytime maximum temperature in the British Isles – even though (in May and early June) it may at the same time be the sunniest place in the country and experiencing its warmest day of the year to date! As sea temperatures do not reach their highest values until late summer, it is at this time when the maximum temperatures on Fair Isle often occur – mostly around 16°C or 17°C. For many years, the 20.2°C recorded in August 1975 remained the highest temperature officially recorded on Fair Isle. Records are usually only beaten by small amounts, but in July 2022 the hottest day was exceeded by 2.4° when the temperature reached 22.6°C.
With little atmospheric pollution (apart from fog), on clear still nights temperatures can fall sharply. Grass frosts, while not frequent, do occur and -10°C is not uncommon, with the lowest temperature of -12.5°C recorded in March 1999. Across the years, a grass frost has been recorded in every month of the year. Air frosts are reported much less frequently and virtually never under calm circumstances. During winter, air temperatures may fall to -2°C or -3°C but are normally around 4°C. The lowest temperature recorded was -5.6°C in February 1998.
The lowest temperatures are usually experienced with an outbreak of cold northerly Arctic air, when strong winds prevent the sea from exerting its usual ameliorating effect. Under such conditions, the wind may gust in excess of 30ms-1, and frequent snow showers and blowing snow often reduce visibility to a few hundred metres or less. Snow or sleet, which used to be frequent and fell on as many as 100 days in a winter, is less so nowadays, falling only on 45 days. A snow cover never lasts long as a change of wind direction to the south always brings milder temperatures and a thaw.
Trends
Dave Wheeler first began keeping a weather notebook in 1952 as a schoolboy. Although Lerwick was his favourite as it was almost always the coldest, he started keeping weather records for Fair Isle in January 1974 when the Met Office established the weather station at Field. In the ensuing years he has accrued four 30-year climate datasets, and is now into the fifth: 1974–90, 1971–2000, 1981–2010, 1991–2020, 2001–24+. In 2002 Dave was awarded an MBE by the Queen at Buckingham Palace for Service to Weather on Fair Isle.
While the long term mean masks a considerable variation in the year-to-year data, there are trends apparent in the datasets. A mild and windy period in the mid to late seventies was followed by a cooler, less windy period for much of the eighties. There was then a return to milder and much windier conditions – with January 1993 having a 3-week period of storms, possibly unparalleled in the past 400 years. In that month the Good Shepherd was stormbound for 3 weeks and even aircraft were unable to reach the island for 10 days due to the high winds.
On a much shorter timescale, it is also possible to see cyclical variations in the yearly weather of the island – with periods of warmth, windy & unsettled weather, or cold & snow occurring on more or less the same days each year.
