Which contraction is used to denote clear skies at a manual observation site?

The contraction used to denote clear skies at a manual observation site is "SKC." This abbreviation stands for "sky clear," which is a standard meteorological term indicating that there are no significant clouds present in the sky. In aviation weather observations, SKC is commonly used to provide pilots and meteorologists with a concise understanding of the favorable sky conditions that may exist, crucial for flight operations and safety.

The other abbreviations convey different meanings. For example, CLR is often informally associated with clear conditions but is not the official term used in meteorology. CLE does not have a recognized meaning in this context, while OVC stands for "overcast," indicating that the sky is completely covered with clouds, which is the opposite of clear skies. Understanding these terms is essential for accurate interpretation of weather reports in aviation contexts.