If the weather is reported as 100' OVC, what is the main concern?

When the weather is reported as 100' OVC (overcast), the main concern relates to low ceiling. The term "OVC" indicates that the clouds are completely covering the sky, and "100'" specifies that this cloud layer is at 100 feet above the ground.

In aviation and meteorology, a ceiling refers to the height of the lowest layer of clouds that are reported as overcast or broken. A cloud base at 100 feet poses significant challenges for visibility and flight operations, making it very low. Pilots require a minimum ceiling for safe take-offs and landings, so having a cloud base that low can restrict visibility, making it difficult or impossible for visual flight rules (VFR) operations.

While visibility restrictions can be a concern of low clouds, the specific challenge presented here is primarily the very low ceiling itself, which has notable implications for safe flight operations.