Mountains influence climate from local and regional scales to even the scale of the whole global climate. At the local scale mountains force air to rise, and consequently assist the development of clouds and precipitation. Mountains tend to have much wetter climates than the surrounding plains, particular those low-lying areas downwind in the rain shadow. Parts of highland Scotland, for example, can receive over 100 inches or 2,500 millimetres of precipitation every year, whilst on the east coast, totals may not exceed 30 inches or 750 millimetres.
There is now little doubt that the presence of mountain ranges on the Earth can dramatically influence global climate. Most airflow in the Earth's atmosphere is orientated along east-west trends, on account of the Earth's rotation and Coriolis force. Consequently, north-south orientated mountain ranges have the ability to influence the general circulation. Although some air is forced to rise over mountains, generating localised weather phenomena due to the uplift of air, the eastward trajectories of large air masses are generally deflected by north-south orientated mountain chains.
The Rocky Mountains that stretch along the western side of North America, for example, deflect air to the north, which cools in the polar latitudes before returning south. The colder northwesterly wind influences the climates of the Canadian and United States interiors, and winter temperatures can be exceedingly low.