Measured ceiling

From Glossary of Meteorology

measured ceiling

After U.S. weather observing practice, the ceiling classification that is applied when the ceiling value has been determined by means of 1) a ceiling light or ceilometer, provided that penetration of the beam is not in excess of that normally experienced for the height and type of layer and that the elevation angle indicated by the clinometer or ceilometer detector does not exceed 84°; 2) the timed disappearance of a radiosonde balloon with its height computed; 3) the known heights of unobscured portions of objects, other than natural landmarks, within 1½ nautical miles of any runway of the airport.

A measured ceiling pertains only to clouds or to obscuring phenomena aloft. It is designated M in aviation weather observations.

Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.