Under which condition would a SPECI report be issued?

A SPECI report, which stands for "Special Weather Report," is issued to provide significant weather updates that deviate from the current METAR report. When the ceiling forms below 1,000 feet, it represents a critical change in flight safety conditions, particularly for visual flight rules (VFR) operations. This condition indicates potentially hazardous weather for aircraft, necessitating immediate reporting to ensure that pilots have the most current and relevant information regarding their operational environment.

The establishment of a low ceiling can impact the ability of pilots to navigate visually and may require them to switch to instrument flight rules (IFR). Therefore, this scenario warrants the issuance of a SPECI report to inform and alert pilots about the imminent change in flying conditions.

In contrast, while other conditions such as an increase in visibility or changes in cloud cover might also affect operations, they do not represent the same immediate level of urgency as a ceiling dropping below 1,000 feet. Calm or light winds, while relevant to flight operations, are typically not factors that invoke a SPECI report unless accompanied by other significant weather changes.