A weather observing station at a sufficiently high elevation to be nonrepresentative of conditions near sea level; 2000 m (about 6500 ft) has been given as a reasonable lower limit. High-altitude stations may be divided into 1) mountain stations, which are freely exposed on or near the summits of peaks and at which observations nearly approximate the free-air conditions at their level, and 2) plateau stations, which have an extreme kind of continental climate.