What area size will cause an AIRMET-S to be upgraded to a SIGMET when covered?

An AIRMET-S (AIRMET for Site) is a weather advisory that warns of potentially hazardous conditions for smaller aircraft, while a SIGMET (Significant Meteorological Information) denotes more serious weather phenomena that can impact a larger area. The threshold for upgrading an AIRMET-S to a SIGMET is significant because it reflects the extent of potential impact on flight operations.

When an AIRMET-S covers an area greater than 3,000 square miles, it indicates that the hazardous conditions are extensive enough to warrant a higher level of alert. This change in classification stems from the recognition that the greater the area affected, the more likely that many aircraft operations will be influenced by those conditions.

Thus, the correct option highlights the substantial area that necessitates heightened caution and attention from pilots and dispatchers, ensuring that safety measures are taken across a broader spectrum of airspace. The larger scale also indicates a potentially higher intensity or complexity of the weather phenomena, justifying the elevation in alert status.