partial obscuration—A designation of sky cover when part of the sky is hidden by surface based obscuring phenomena.
pilot balloon—A small free-lift balloon used to determine the speed and direction of winds in the upper air.
PARTIAL OBSCURATION Denotes that 1/8th or more of the sky, but not all of the sky, is hidden by any surface-based phenomena in the atmosphere, excluding precipitation. It often reduces horizontal visibility but not the vertical.
The following classifications are used in aviation weather observations: clear, scattered, broken, overcast, partial obscuration, obscuration. Skyhook balloon A large plastic constant-level balloon for duration flying at very high altitudes.
The summation amount for any given layer is equal to the sum of the sky cover for the layer being evaluated plus the sky cover for all lower layers, including partial obscuration. A summation amount for a layer can not exceed 8/8ths.
It is encoded "X" in aviation weather observations; it always constitutes a ceiling, the height of which is the value of vertical visibility into the obscuring phenomenon. Compare partial obscuration. 2. A surface-based obscuring phenomenon.
include blowing and widespread dust, fog (including freezing fog and patchy fog), haze, mist, sand and blowing sand, smoke, blowing spray, and volcanic ash. It is reported as "X" in an observation and on the METAR. Related term: partial obscuration ...
Amount of sky cover for any given level is determined according to the summation principle. The following classifications of sky cover are used in aviation weather observations: clear, scattered, broken, overcast, partial obscuration, obscuration.
 See also: Surface, Partial, Obscuration, Earth, Weather
  
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