Think of it yet another way. The Shetland Islands, which lie to the North of the Scottish mainland, are further North than the Southern tip of Greenland, but enjoy a much milder climate. Click here to view maps of Scottish climate in relation to the rest of the world. Prevailing winds are from the west or southwest, and annual rainfall ranges from over 60 inches in the west to less than 20 inches in the east. Winters are not particularly cold but usually quite wet.
Snow does fall, increasingly so away from the coast and on high ground.
Northeast winds in particular can bring prolonged low temperatures, and the record low temperature for Scotland is about minus 28 degrees Celsius. Click here to view maps of Scottish rainfall data. These are averaged and generalised figures, and there is much local variation due to altitude and distance from the coast. However it is likely that the Northern limit of their natural range is reached somewhere in the Northern half of the country, being determined by a subtle blend of factors such as rainfall, temperature and wind exposure. Feral colonies seem able to survive without human intervention certainly as far north as the coastal parts of Sutherland, but not much further.