The prevailing winds along the Great Glen are from the southwest. As warm air approaches the west of Scotland from the direction of central America it collects a great deal of moisture. Most of this is deposited over the high ground in the west of Scotland. Rainfall records show that from 75 inches (1,900mm) in Fort William at the western end of the Great Glen, the rainfall drops off at about one inch (25.4mm) per mile as you head along the glen towards Inverness. 42 inches (1070mm) falls on Fort Augustus at the west end of Loch Ness and this drops to 23 inches (600mm) at Inverness. [Based on 1989 statistics.]
At 56o north, the Great Glen has long summer days and winter nights, but overall, owing mainly to the warmth of the Gulf Stream, the climate is quite pleasant. Rainfall is high, but winters are not particularly severe. In the last twenty-four years the main loch-side A82 between Fort Augustus and Inverness has not been blocked by snow for more than an hour or two, landslips and fallen trees causing far more disruption. With the bulk of Loch Ness holding an even 42oF (5oC) it acts like a giant radiator helping to reduce the amount of ice and snow on the loch-side roads.
If you are coming to visit the area it is recommended that you bring a raincoat and umbrella whatever time of year and, in the winter, be prepared for temperatures below freezing exacerbated with wind chill some days. Winter days are not always cold, however, and it is often possible to where little more than a sweatshirt on milder days.
The Great Glen does tend to have its own micro-climate and rain forecast for the north of Scotland often misses the glen completely and the Webmaster has had many a battle with the meteorological office over inaccurate forecasts for the area.
The least crowded and most attractive times to visit the area are in May, June, September and October. My particular favourite time is June with the long summer evenings. If you have the energy it is daylight from 3am to 11pm so you can tour, or watch for Nessie, for 20 hours a day.
Winters are relatively mild and although temperatures down to -10oC (14oF) are not unusual, it is much more likely to be around freezing and often several degrees above freezing. The photograph shows the bad winter of 1985 when we had around half a metre of snow (19 inches), but usually we only have two or three much small falls in the region of 10 - 15cm (4 to 6 inches) which quickly melts except on the hill tops. This page has been updated as at 1st March 2001 and snow in the region of 15cm (6 inches) is lying outside my house (shown in picture). Drifting, however, in strong winds has built up to over 3 feet (90cm) in one or two places. The A82 road along the side of the loch is rarely blocked with snow, only twice in 22 years I have lived here, and then only for a few hours.
Much of the Great Glen is mountainous. The hilltops are either rocky or boggy with only some sheep and cattle farming along most of the glen. Even this is absent along the steep sides of Loch Ness where the only crop is timber. The Forestry Commission planted huge forests of larch and spruce along most of the slopes and this is now being harvested. Discovering that clear-cutting was harming the wildlife and causing topsoil to be lost, modern timber cropping is undertaken selectively or in small patches.
Apart from the towns of Inverness and Fort William, the major industries within the walls of the glen itself are Forestry, hydro-electricity production and tourism. Eskers, made up of gravels piled up under the ice sheet during the ice age are excavated for building gravel near Inverness.