What cloud condition triggers a SPECI criterion?

• A. When broken (BKN) or overcast (OVC) below aerodrome's highest alternate minimum cloud base or 1500 ft, whichever is greater
• B. Scattered clouds above 6000 ft
• C. Clear sky
• D. Low-lying fog

Answer: (A)

Special weather reports are issued when weather changes are significant enough to affect flight safety, especially ceilings that determine instrument approaches and alternate planning. The triggering cloud condition is when the sky is broken or overcast and the ceiling falls below the aerodrome’s highest alternate minimum cloud base, or 1500 ft, whichever is greater. This threshold matters because it signals a drop in usable approach minima and the potential need to delay, divert, or replan operations; a lower ceiling directly reduces the safety margins for arrivals and departures, so pilots and controllers need an immediate, formal update.

Scattered clouds high above, clear skies, or fog conditions that don’t reach that particular ceiling threshold don’t meet this specific SPECI criterion, so they wouldn’t by themselves trigger a SPECI under this rule.