A few clouds...
Why is the term Ceiling so hard to define. I can not understand how many people don't know what it means.
Some have no idea where I have seen it in the forecast. I have asked people that have reported the weather on TV. My dictionary even avoids it having any connection with the weather. Will you please enlighten us?
- The American Meteorological Society has a glossary of meteorology at http://amsglossary.allenpress.com/glossary, in which they define ceiling, as used in aviation meteorology as:
1. After U.S. weather observing practice, the ceiling classification applied when the reported ceiling value has been determined by a pilot while in flight within one and one-half nautical miles of any runway of the airport.
Aircraft ceilings may refer to vertical visibility or obscuring phenomena aloft as well as to clouds, and are designated A in aviation weather observations. 2. The maximum altitude at which any given aircraft can be operated safely.
From my experience serving the ICAO it was the lowest height (viewed from the ground) at which the clouds covered more than half of the sky. This "half" is a running total, meaning it includes the portions of the sky covered by lower clouds as well. In a METAR
(aviation weather observation report), the height at which BKN (or OVC otherwise) cloud coverages are first reported comprises the ceiling. Some national jurisdictions include an opacity requirement for those clouds as well.
What does a ceilometer report? The definition(s) above require a human observer to assess the fraction of sky obscured. Automated weather stations use a laser projecting robot called a ceilometer; it detects the distance to a certain level of attenuation of reflected light to assign a height to a specific spot in the sky. A single unit is not designed to assess the whole sky.more weather and cloud information