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

When the weather is reported as 100' OVC, this indicates that the ceiling is extremely low, with overcast clouds observed at 100 feet above ground level. The primary concern in this scenario is related to the low ceiling, as it can significantly affect the safety of flight operations.

A low ceiling limits visibility, necessitating pilots to operate under instrument flight rules (IFR) due to reduced vertical space for aircraft to maneuver. Furthermore, such low cloud cover can inhibit a pilot’s ability to gauge altitude and approach for takeoff or landing, which can be particularly dangerous if not properly managed.

Although visibility can also be adversely affected under low cloud conditions, the immediate and critical concern is the limited vertical space, creating an urgent need for careful flight planning and adherence to regulations in low-visibility situations.