The Cairngorm mountains form the largest area of continuous high ground in Britain. They act as a major originator of weather events and their effects are transmitted downstream to the middle and lower catchment in terms of flood peaks.
The NE of Scotland is unusual that it doesn’t get most of its rainfall from the warm, humid south-westerly winds which sweep in from the Atlantic. Instead, cold rains come across the North Sea, showers and snow from the north and north-east. Winds across the North Sea bring the haar, a cold summer mist up to 20 miles west of the coast. Further inland, the Cairngorm uplands have a beneficial ‘foehn’ effect, providing a rain-shadow against westerly winds. As a result of these factors the annual average precipitation ranges from 2100 mm in the Cairngorms to 810 mm at Aberdeen . In the Cairngorms, during the winter months, much of this precipitation falls as snow, and above 800m can account for approximately 30% of annual precipitation . Snow is an important hydrological component in the upland region of the catchment.
The region has a cool temperate climate with an annual mean temperature of 8°C. The length and east-west orientation of the catchment results in its upper parts, especially the valley floors, a relatively continental climate, with wide annual ranges of temperature. The growing season is conventionally defined as the number of days of mean temperature >5.6°C. In the agricultural areas this ranges from 241 days at Aberdeen (24 m a.s.l.) to 207 days at Logie Coldstone (184 m a.s.l.) . Gales occur on average 5 days a year over the inland area, but increase with frequency on exposed mountains and the coast.
Some of the most extreme climate in the UK is associated with this catchment:
The lowest UK air temperature at Braemar (-27.2°C, Jan 1982/Feb 1895)
A gust of 101 mph at Dyce, Aberdeen (Jan 1953)
A morning to afternoon range of temperature at Aboyne of -1 to 22°C (Sept 2004)