An evaluation, according to set procedure, of those weather elements that are most important for aircraft operations. It always includes the cloud height or vertical visibility, sky cover, visibility, obstructions to vision, certain atmospheric phenomena, and wind speed and direction that prevail at the time of the observation. Complete observations include the sea level pressure, temperature, dewpoint temperature, and altimeter setting. Aviation weather observations are further classified as record, special, check, and local extra observations. The first two types are encoded and transmitted as reports on communications circuits. Compare synoptic weather observation.