Upslope fog is a type of fog most commonly found in mountain ranges near the sea. It occurs when moist air is blown up a hillside to a temperature at which condensation occurs, forming wispy clouds. Upslope fog often encircles the base-to-middle of a mountain or group of slopes, anywhere up to 300 meters above ground. The chains of fog can span hundreds of miles. As with any other type of fog, visibility remains restricted in certain areas. This common weather phenomenon predominantly occurs in winter months when colder maritime air is more likely to drift inward.